TRS-80 DOS – TRSDOS v1.3 – SYS06/SYS Disassembled – Ira Goldklang's TRS-80 Revived Site

General:

SYS6 handles the following DOS Commands: APPEND, ATTRIB, AUTO, BUILD, CLEAR, CLOCK, CREATE, DATE, DIR, DO, DUMP, ERROR, FREE, LIB, LOAD, PAUSE, PROT, RENAME, and TIME

On Entry, Register C must hold the order number of the command and Register Pair HL the Buffer Input Line.

Disassembly:

ORG 5200H

“BEGIN”
5200

PUSH HL

Save Register HL (i.e., the pointer to the command line entered by the USER after the library command itself) to the top of the stack.

5201

XOR A

Set Register A to ZERO and clear all Flags.

5202

LD (FLAG1),A

Indicate that no overlay is resident by storing the value held in Register A (i.e., a zero) into the memory location 4414H.
NOTE: 4414H is the storage location for the NUMBER OF THE OVERLAY CURRENTLY IN MEMORY.

5205

LD (SCAFLG),A

Clear the protection override switch by storing the value held in Register A (i.e., a zero) into the memory location 42FFH.
NOTE: 42FFH is the storage location for whether a password check is skipped or undertaken in an OPEN command. If Bit 0 is set, the check is skipped.

5208

DEC A

DECrement the value stored in Register A by 1 so that A will be FFH.

5209

LD (BASICG),A

Signify that BASIC is NOT in RAM flag by storing the value held in Register A (i.e., FFH) into the memory location 427AH.
NOTE: 427AH is the storage location for the EXECUTE FILE FLAG.

520C

CALL GETTAB
[529BH]

GOSUB to 529BH to parse the table holding the execution addresses of the various commands looking for a match against the requested command number, held in Register C on entry to this overlay.

520F

JR C,BEGIN1
[5213H]

If the C FLAG (Carry) is set then there was an error in finding a match between the routine requested (held in Register C) and the possible routine numbers held in the table, so JUMP to 5213H.

5211

EX (SP),HL

EXchange the value stored in Register Pair HL with the value stored in Register Pair (SP).

5212

RET

RETurn to the caller.

5213H – Continuation of the above initial processing routine. Jumped here if there was no routine match.

“BEGIN1”
5213

POP HL

Restore the passed input line from the top of the stack into Register Pair HL.

“ERR2”
5214

LD A,ERICP

LET Register A = 0BH, which is the code for an ILLEGAL PARAMETER error.

5216

JR ERRX
[523AH]

JUMP to 523AH to continue.

5218H – Process a PARAMETER NOT FOUND error.

“ERR3”
5218

LD A,ERCPM

LET Register A = 0AH, which is the code for an PARAMETER NOT FOUND error.

521A

JR ERRX
[523AH]

JUMP to 523AH to continue.

521CH – Process a FILE ALREADY EXISTS error.

“ERR1”
521C

LD A,EFAT

LET Register A = 28H, which is the code for an FILE ALREADY EXISTS error.

521E

JR ERRX
[523AH]

JUMP to 523AH to continue.

5220H – Display “END LESS THAN START” and RETurn.

“ERR5”
5220

LD HL,MES5

LET Register Pair HL = 5240H which points to the message “END LESS THAN START” + 0DH.

5223

JR ERRY
[523DH]

JUMP to 523DH (which, in turn, jumps to 021BH in the ROM to display a message pointed to by HL and then RETurns), to continue.

5225H – Display “START LESS THAN 6000” and RETurn.

“ERR6”
5225

LD HL,MES6

LET Register Pair HL = 5254H which points to the message “START LESS THAN 6000” + 0DH.

5228

JR ERRY
[523DH]

JUMP to 523DH (which, in turn, jumps to 021BH in the ROM to display a message pointed to by HL and then RETurns), to continue.

522AH – Display “MEMORY FAULT AT X ‘nnnn'” and RETurn.

“ERR7”
522A

LD HL,BADRAM

LET Register Pair HL = 5269H which points to the message “MEMORY FAULT AT X ‘nnnn’” + 0DH.

522D

JR ERRY
[523DH]

JUMP to 523DH (which, in turn, jumps to 021BH in the ROM to display a message pointed to by HL and then RETurns), to continue.

522FH – Display “LRL OF FILES DO NOT MATCH” and RETurn.

“ERR13”
522F

LD HL,BADLRL

LET Register Pair HL = 5281H which points to the message “LRL OF FILES DO NOT MATCH” + 0DH.

5232

JR ERRY
[523DH]

JUMP to 523DH (which, in turn, jumps to 021BH in the ROM to display a message pointed to by HL and then RETurns), to continue.

5234H – Process a DISK DRIVE NOT ON error.

“ERR9”
5234

LD A,EDNS

LET Register A = 02H, which is the code for a DISK DRIVE NOT ON error.

5236

JR ERR
[523AH]

JUMP to 523AH to continue.

5238H – Process a FILE ACCESS DENIED error.

5238

LD A,EFAD
“ERR4”

LET Register A = 28H, which is the code for a FILE ACCESS DENIED error.

“ERRX”
523A

JP ERR
[6132H]

JUMP to the DOS ERROR routine at 6132H.

523DH – Display the message pointed to by Register Pair HL via the ROM and RETurn.

“ERRY”
523D

JP PRINT
[021BH]

JUMP to 021BH.
NOTE: 021BH will display the character at (HL) until a 03H is found.

5240H – Message Storage Area.

“MESS5”
5240

DEFM

“END LESS THAN START” + 0DH.

“MESS6”
5254

DEFM

“START LESS THAN 6000” + 0DH.

“BADRAM”
5269

DEFM

“MEMORY FAULT AT X ‘nnnn’” + 0DH.

“BADLRL”
5281

DEFM

“LRL OF FILES DO NOT MATCH” + 0DH.

529BH – Routine to Parse the Table of Functions looking to match the requested function number (held in Register C on entry).

“GETTAB”
529B

LD HL,TABCOM

LET Register Pair HL = 52B3H to point to the table of functions in this Overlay.

“GETTA1”
529E

LD A,(HL)

Fetch the value stored at memory location pointed to by Register Pair HL (i.e., the command number in the table) and put it into Register A.

529F

OR A

Since a LD command does not set any FLAGS, Set FLAGS based on the contents of Register A.

52A0

JR Z,NOTFND
[52B1H]

If the command number in the table is zero, then we have run out of table entries to match against but did not have a match, so JUMP to 52B1H.

52A2

CP C

Compare the value held in Register A (i.e., the command number which HL is pointing to in the table of functions) against the value held in Register C (i.e., the command number passed on entry). Results: If Register A equals C, the Z FLAG is set; otherwise the NZ FLAG is set.

52A3

JR Z,FOUND
[52AAH]

If the Z FLAG (Zero) is set, then the command number requested (i.e., Register C) matches the current entry in the lookup table (pointed to by [HL]), so JUMP to 52AAH.

52A6
52A5
52A7

INC HL
INC HL
INC HL

If we’re here then we didn’t get a match in the command table lookup, so we need to move the table pointer (i.e., Register Pair HL) 3 entries down the table.

52A8

JR GETTA1
[529EH]

LOOP BACK to the top of this routine to 529EH.

52AAH – Continuation of the routine to Parse the Table of Functions. If we are here, then HL is pointing to the entry in the lookup table which matches the desired routine held in Register C on entry.

“FOUND”
52AA

INC HL

Bump the value stored in Register Pair HL by 1 so that HL now points to the LSB of the routine address for the matching routine.

52AB

LD E,(HL)

Fetch the value stored at memory location pointed to by Register Pair HL, which will be the LSB of the address of the matching routine, and put it into Register E.

52AC

INC HL

Bump the value stored in Register Pair HL by 1 to point to the MSB of the routine address for the matching routine.

52AD

LD D,(HL)

Fetch the value stored at memory location pointed to by Register Pair HL, which will be the MSB of the address of the matching routine, and put it into Register D.

52AE

EX DE,HL

EXchange the value stored in Register Pair HL (i.e., the pointer to the MSB of the routine address for the matching routine) with the value stored in Register Pair DE (i.e., the address of the matching routine).

52AF

OR A

Set FLAGS based on the contents of Register A, which also clears the CARRY FLAG (which acts as the error flag).

52B0

RET

RETurn to the caller.

52B1H – Continuation of the routine to Parse the Table of Functions. If we are here, then we parsed the table of functions but did not fine one which matches the requested function number (held in Register C on entry).

“NOTFND”
52B1

SCF

Set the CARRY FLAG to signify that there was an error.

52B2

RET

RETurn to the caller.

52B3H – Table of Functions in this Overlay.

“TABCOM”
52B3H

APPEND command number.

52B4H

568EH

APPEND command routine address.

52B6H

ATTRIB command number.

52B7H

585EH

ATTRIB command routine address.

52B9H

AUTO command number.

52BAH

52EDH

AUTO command routine address.

52BCH

BUILD command number.

52BDH

5FC9H

BUILD command routine address.

52BFH

CLEAR command number.

52C0H

5EFFH

CLEAR command routine address.

52C2H

CLOCK command number.

52C3H

53E2H

CLOCK command routine address.

52C5H

CREATE command number.

52C6H

5E52H

CREATE command routine address.

52C8H

DATE command number.

52C9H

5361H

DATE command routine address.

52CBH

DIR command number.

52CCH

59D9H

DIR command routine address.

52CEH

DO command number.

52CFH

603DH

DO command routine address.

52D1H

DUMP command number.

52D2H

5700H

DUMP command routine address.

52D4H

ERROR command number.

52D5H

6114H

ERROR command routine address.

52D7H

FREE command number.

52D8H

5CDCH

FREE command routine address.

52DAH

LIB command number.

52DBH

5423H

LIB command routine address.

52DDH

LOAD command number.

52DEH

584FH

LOAD command routine address.

52E0H

PAUSE command number.

52E1H

60CFH

PAUSE command routine address.

52E3H

PROT command number.

52E4H

5455H

PROT command routine address.

52E6H

RENAME command number.

52E7H

559FH

RENAME command routine address.

52E9H

TIME command number.

52EAH

53ABH

TIME command routine address.

52ECH

End of Table Delimeter.

52EDH – AUTO Library Command – Function 3

“AUTO”
52ED

LD A,(HL)

Fetch the first character stored at memory location pointed to by Register Pair HL (i.e., the command line which was passed to this Overlay on entry) and put it into Register A.

52EE

CP 3AH

Prepare to test for a DRIVE NUMBER by comparing the value held in Register A against 3AH (ASCII: :). Results: If Register A equals :, the Z FLAG is set; otherwise the NZ FLAG is set.

52F0

JR NZ,AUTO2
[52FFH]

If we did not get a : the NZ FLAG (Not Zero) is set, so JUMP to 52FFH.

52F2

INC HL

Bump the value stored in Register Pair HL by 1 so as to point to the second character stored at memory location pointed to by Register Pair HL (i.e., the command line which was passed to this Overlay on entry).

52F3

LD A,(HL)

Fetch the second character from the command line (i.e., the memory location pointed to by Register Pair HL) and put it into Register A.

52F4

SUB 30H

SUBtract the value 30H from Register A. Note: Subtracting 30H from from Register A will convert an ASCII number ‘0’-‘9’ to its decimal equivalent (i.e., 6 in ASCII is 36H in Hex; so 36H-30H = 6).

52F6

LD (AUTDRV),A

Store the value held in Register A (which should be the decimal equivalent of the specified drive number) into the memory location 5301H (which is in the middle of a LD C,nnH OPCODE).

“AUTO1”
52F9

INC HL

Bump the value stored in Register Pair HL by 1 to point to the next character stored at memory location pointed to by Register Pair HL (i.e., the command line which was passed to this Overlay on entry).

52FA

LD A,(HL)

Fetch the next character from the command line (i.e., the memory location pointed to by Register Pair HL) and put it into Register A.

52FB

CP 20H

Compare the value held in Register A against 20H (ASCII: SPACE). Results: If Register A equals SPACE, the Z FLAG is set; otherwise the NZ FLAG is set.

52FD

JR Z,AUTO1
[52F9H]

If the Z FLAG (Zero) is set then we got a SPACE so LOOP back to 52F9H to check the next character.

“AUTO2”
52FF

PUSH HL

Save Register HL (i.e., the current parsed location in the command line which was passed to this Overlay on entry) to the top of the stack.

5300

LD C,nnH
LD C,AUTDRV

LET Register C = the drive number received, as has been filled in at 52F6H.

5302

CALL RDGAT
[4A93H]

GOSUB to 4A93H.
NOTE: 4A93H is the SYS00/SYS routine to READ THE GAT SECTOR INTO RAM (Buffer at 4D00H).

5305

POP HL

Restore the current parsed location in the command line which was passed to this Overlay on entry from the top of the STACK into Register Pair HL.

5306

JP NZ,ERR
[6132H]

If the NZ FLAG (Not Zero) is set then the READ THE GAT SECTOR routine returned with an error so JUMP to 6132H.

5309

PUSH HL

Save the current parsed location in the command line which was passed to this Overlay on entry held in Register Pair HL to the top of the STACK.

530A

LD B,01H

LET Register B = 01H to prepare for using B as a counter.

“AUTO3”
530C

LD A,(HL)

Fetch the next character from the command line (i.e., the memory location pointed to by Register Pair HL) and put it into Register A.

530D

CP 20H

Compare the value held in Register A against a SPACE. Results:

If Register A equals SPACE, the Z FLAG is set.
If A < SPACE, the CARRY FLAG will be set.
if A >= SPACE, the NO CARRY FLAG will be set.

530F

JR C,AUTO4
[5315H]

If the C FLAG (Carry) is set then A < SPACE, meaning we have a control character, so JUMP to 5315H.

5311

INC HL

Bump the value stored in Register Pair HL by 1 so as to point HL to the next character from the command line .

5312

INC B

Bump the value stored in Register B (which is acting as a counter) by 1.

5313

JR AUTO3
[530CH]

LOOP BACK to 530CH to keep parsing the command line.

5315H – Continuation of the AUTO command; jumped here if there was a command character found in the passed command line. This routine will fill the command line to be 31 chararcters (with spaces) and put it into the appropriate location in the GAT sector.

“AUTO4”
5315

LD A,20H

LET Register A = 20H (Decimal: 32), which is the maximum length of a valid AUTO command.

5317

SUB B

SUBtract the value held in Register B (i.e., the number of characters used) from Register A (i.e., the number of possible characters), thus leaving Register A holding the number of spaces left.

5318

LD B,A

LET Register B = Register A (i.e., the number of characters left on a full command line).

5319

INC HL

Bump the value stored in Register Pair HL by 1 so as to point HL to the next character from the command line.

“AUTO5”
531A

LD (HL),20H

Store a SPACE into the memory location pointed to by Register Pair HL.

531C

INC HL

Bump the value stored in Register Pair HL by 1 so as to point HL to the next character from the command line.

531D

DJNZ AUTO5

LOOP back to 531AH until Register B is ZERO so that all remaining characters on the command line have been turned in to spaces.

531F

POP HL

Restore Register Pair HL (i.e., the pointer to the current location on the command line) from the top of the STACK.

5320

LD DE,BUFF2 + DAUTO

LET Register Pair DE = 4DE0H, which is the memory location of the GAT SECTOR in RAM for the AUTO command.

5323

LD BC,0020H

LET Register Pair BC = 0020H (Decimal: 32), which is the maximum length of a valid AUTO command.

5326

LDIR

Transfers a byte of data from the memory location pointed to by HL to the memory location pointed to by DE. Then HL and DE are incremented and BC is decremented. If BC is not zero, this operation is repeated. Interrupts can trigger while this instruction is processing.

5328

LD A,(AUTDRV)

Fetch the value stored at memory location 5301H (i.e., the applicable drive number) and put it into Register A.

532B

LD C,A

LET Register C = Register A (i.e., the applicable drive number).

532C

CALL WRGAT
[4A9BH]

GOSUB to 4A9BH.
NOTE: 4A9BH is the SYS00/SYS routine to to write the GAT sector from RAM to diskette.

532F

JP NZ,ERR
[6132H]

If the NZ FLAG (Not Zero) is set then the WRITE THE GAT SECTOR routine returned with an error so JUMP to 6132H.

5332

LD HL,AUTMSG

LET Register Pair HL = 5355H, which is a pointer to the AUTO = ” message.

5335

CALL PRINT
[021BH]

GOSUB to 021BH.
NOTE: 021BH will display the character at (HL) until a 03H is found.

5338

LD HL,BUFF2 + DAUTO

LET Register Pair HL = 4DE0H, which is the memory location of the GAT SECTOR in RAM for the AUTO command.

533B

LD A,(HL)

Fetch the value stored at memory location pointed to by Register Pair HL (i.e., the first byte of the AUTO command) and put it into Register A.

533C

CP 20H

Compare the value held in Register A (i.e., the first byte of the AUTO command) against 20H (ASCII: SPACE). Results:

If Register A equals SPACE, the Z FLAG is set.
If A < SPACE, the CARRY FLAG will be set.
if A >= SPACE, the NO CARRY FLAG will be set.

533E

JR C,AUTO8
[534FH]

If A < SPACE, meaning the first byte of the AUTO command is a command code, the C FLAG (Carry) is will be set, so JUMP to 534FH.

5340

PUSH HL

Save Register HL (i.e., the memory location of the GAT SECTOR in RAM for the AUTO command) to the top of the STACK.

“AUTO6”
5341

LD A,(HL)

Fetch the value stored at memory location (i.e., a letter of the AUTO command) pointed to by Register Pair HL and put it into Register A.

5342

CP 20H

Compare the value held in Register A (i.e., the first byte of the AUTO command) against 20H (ASCII: SPACE). Results:

If Register A equals SPACE, the Z FLAG is set.
If A < SPACE, the CARRY FLAG will be set.
if A >= SPACE, the NO CARRY FLAG will be set.

5344

JR C,AUTO7
[5349H]

If A < SPACE, meaning the current byte of the AUTO command is a command code, the C FLAG (Carry) is will be set, so JUMP to 5349H.

5346

INC HL

Bump the value stored in Register Pair HL (i.e., the pointer to a byte of the AUTO command) by 1.

5347

JR AUTO6
[5341H]

LOOP BACK to 5341H to keep parsing the AUTO command.

5349H – Continuation of the AUTO command; jumped here if we reached the end of the AUTO command as stored in the GAT sector.

“AUTO7”
5349

LD (HL),03H

Store an 03H (i.e., a standard terminator) into the memory location (i.e., the control character in the AUTO command) pointed to by Register Pair HL, because an 03H terminator is required by the ROM routine at 021BH.

534B

POP HL

Restore the memory location of the GAT SECTOR in RAM for the AUTO command from the top of the STACK into Register Pair HL.

534C

CALL PRINT
[021BH]

GOSUB to 021BH.
NOTE: 021BH is the routine in the Model III ROM which will display the character at (HL) until a 03H is found.

“AUTO8”
534F

LD HL,AUTNUL

LET Register Pair HL = 535FH, which is the message storage area for ‘.

5352

JP PRINT
[021BH]

JUMP to 021BH.
NOTE: 021BH will display the character at (HL) until a 03H is found.

5355H – AUTO COMMAND MESSAGE STORAGE AREA.

“AUTMSG”
5355

DEFM …

“AUTO = ‘”.

“AUTNUL”
535F

DEFB …

“‘”.

5361H – DATE Library Command – Function 11

“S6DATE”
5361

LD C,2FH

LET Register C = 2FH (ASCII: /).

5363

LD A,(HL)

Fetch the value stored at memory location pointed to by Register Pair HL (i.e., the command line which was passed to this overlay) and put it into Register A.

5364

CP 0DH

Compare the value held in Register A against 0DH (ASCII: CARRIAGE RETURN). Results: If Register A equals CARRIAGE RETURN, the Z FLAG is set; otherwise the NZ FLAG is set.

5366

JP Z,MSGPRT
[61EAH]

If the Z FLAG (Zero) is set then we are at a CARRIAGE RETURN, meaning we are at the end of the passed command line, so JUMP to 61EAH to then display the time and the date.

5369

CP 03H

Compare the value held in Register A against 03H (i.e., a standard terminator). Results: If Register A equals 03H, the Z FLAG is set; otherwise the NZ FLAG is set.

536B

JP Z,MSGPRT
[61EAH]

If the Z FLAG (Zero) is set then we have a terminator in the passed command line, so JUMP to 61EAH to then display the time and the date.

536E

CALL CONV1
[53EEH]

GOSUB to 53EEH to decode the date.

5371

JP NZ,ERR2
[5214H]

If the prior CALL returned with NZ set, that signifies that it exited with an error. If that is the case, JUMP to 5214H.

5374

LD A,(BIN)

Fetch the value stored at memory location 53EBH (i.e., the YEAR or SECOND) and put it into Register A.

5377

CP 64H

Compare the value held in Register A against 64H (Decimal: 100). Results:

If Register A equals 100, the Z FLAG is set.
If A < 100, the CARRY FLAG will be set.
if A >= 100, the NO CARRY FLAG will be set.

5379

JP NC,ERR2
[5214H]

If A >= 100 then we have a bad YEAR (and the NC FLAG will be set), so JUMP to 5214H.

537C

LD A,(BIN + 1)

Fetch the value stored at memory location 53ECH (i.e., the DAY or MINUTE) and put it into Register A.

537F

CP 20H

Compare the value held in Register A against 20H (Decimal: 32). Results:

If Register A equals 32, the Z FLAG is set.
If A < 32, the CARRY FLAG will be set.
if A >= 32, the NO CARRY FLAG will be set.

5381

JP NC,ERR2
[5214H]

If A >= 32 then we have a bad DAY (and the NC FLAG will be set), so JUMP to 5214H.

5384

OR A

Set FLAGS based on the contents of Register A.

5385

JP Z,ERR2
[5214H]

If the MONTH is 0, then we have a bad MONTH (and the Z FLAG will be set), so JUMP to 5214H.

5388

LD A,(BIN+2)

Fetch the value stored at memory location 53EDH (i.e., the MONTH or HOUR) and put it into Register A.

538B

CP 0DH

Compare the value held in Register A against 0DH (Decimal: 13). Results:

If Register A equals 13, the Z FLAG is set.
If A < 13, the CARRY FLAG will be set.
if A >= 13, the NO CARRY FLAG will be set.

538D

JP NC,ERR2
[5214H]

If A >= 13 then we have a bad MONTH (and the NC FLAG will be set), so JUMP to 5214H.

5390

OR A

Set FLAGS based on the contents of Register A.

5391

JP Z,ERR2
[5214H]

If the DAY is 0, then we have a bad DAY (and the Z FLAG will be set), so JUMP to 5214H.

5394

LD HL,BIN

LET Register Pair HL = 53EBH (i.e., the first byte of the 3 bytes comprising a DATE or TIME).

5397

LD DE,YEAR

LET Register Pair DE = 421AH, which will be the destination for the 3 numbers comprising the date.

539A

LD BC,0003H

LET Register Pair BC = 0003H, to signify 3 bytes to move.

539D

LDIR

539F

LD HL,BIN

LET Register Pair HL = 53EBH (i.e., the first byte of the 3 bytes comprising a DATE or TIME).

53A2

LD DE,DTSAVE

LET Register Pair DE = 42B7H, which will be the destination for the 3 numbers comprising the date.

53A5

LD BC,0003H

LET Register Pair BC = 0003H, to signify 3 bytes to move.

53A8

LDIR

53AA

RET

RETurn to the caller.

53ABH – TIME Library Command – Function 36

“S6TIME”
53AB

LD C,3AH

LET Register C = 3AH (ASCII: :).

53AD

LD A,(HL)

Fetch the value stored at memory location pointed to by Register Pair HL (i.e., the command line which was passed to this overlay) and put it into Register A.

53AE

CP 0DH

Compare the value held in Register A against 0DH (ASCII: CARRIAGE RETURN). Results: If Register A equals CARRIAGE RETURN, the Z FLAG is set; otherwise the NZ FLAG is set.

53B0

JP Z,MSGPRT
[61EAH]

If the Z FLAG (Zero) is set then we are at a CARRIAGE RETURN, meaning we are at the end of the passed command line, so JUMP to 61EAH to then display the time and the date.

53B3

CP 03H

Compare the value held in Register A against 03H (i.e., a standard terminator). Results: If Register A equals 03H, the Z FLAG is set; otherwise the NZ FLAG is set.

53B5

JP Z,MSGPRT
[61EAH]

If the Z FLAG (Zero) is set then we have a terminator in the passed command line, so JUMP to 61EAH to then display the time and the date.

53B8

CALL CONV1
[53EEH]

GOSUB to 53EEH to decode the time.

53BB

JP NZ,ERR2
[5214H]

If the prior CALL returned with NZ set, that signifies that it exited with an error. If that is the case, JUMP to 5214H.

53BE

LD A,(BIN)

Fetch the value stored at memory location 53EBH (i.e., the YEAR or SECOND) and put it into Register A.

53C1

CP 3DH

Compare the value held in Register A against 3DH (Decimal: 61). Results:

If Register A equals 61, the Z FLAG is set.
If A < 61, the CARRY FLAG will be set.
if A >= 61, the NO CARRY FLAG will be set.

53C3

JP NC,ERR2
[5214H]

If A >= 61 then we have a bad SECOND (and the NC FLAG will be set), so JUMP to 5214H.

53C6

LD A,(BIN + 1)

Fetch the value stored at memory location 53ECH (i.e., the DAY or MINUTE) and put it into Register A.

53C9

CP 3DH

Compare the value held in Register A against 3DH (Decimal: 61). Results:

If Register A equals 61, the Z FLAG is set.
If A < 61, the CARRY FLAG will be set.
if A >= 61, the NO CARRY FLAG will be set.

53CB

JP NC,ERR2
[5214H]

If A >= 61 then we have a bad MINUTE (and the NC FLAG will be set), so JUMP to 5214H.

53CE

LD A,(BIN + 2)

Fetch the value stored at memory location 53EDH (i.e., the MONTH or HOUR) and put it into Register A.

53D1

CP 18H

Compare the value held in Register A against 18H (Decimal: 24). Results:

If Register A equals 24, the Z FLAG is set.
If A < 24, the CARRY FLAG will be set.
if A >= 24, the NO CARRY FLAG will be set.

53D3

JP NC,ERR2
[5214H]

If A >= 24 then we have a bad HOUR (and the NC FLAG will be set), so JUMP to 5214H.

53D6

LD HL,BIN

LET Register Pair HL = 53EBH (i.e., the first byte of the 3 bytes comprising a DATE or TIME).

53D9

LD DE,SECOND

LET Register Pair DE = 4217H, which will be the destination for the 3 numbers comprising the time.

53DC

LD BC,0003H

LET Register Pair BC = 0003H, to signify 3 bytes to move.

53DF

LDIR

53E1

RET

RETurn to the caller.

53E2H – CLOCK Library Command – Function 7. Exits with Z FLAG for OFF and NZ FLAG for ON.

“CLOCK”
53E2

CALL CHKFLG
[5081H]

GOSUB to 5081H to evaluate for ON/OFF Parameters.

53E5

JP Z,CLOCKF
[02A1H]

If the Z FLAG (Zero) is set then we received an OFF parameter, so JUMP to 02A1H.
NOTE: 02A1H is the Model III ROM routine to disable the clock display by disabling Bit 0 of 4210H.

53E8

JP CLOCKN
[0298H]

JUMP to 0298H.
NOTE: 02A1H is the Model III ROM routine to enable the clock display by enabling Bit 0 of 4210H.

53EBH – BYTE STORAGE AREA FOR TIME AND DATE ROUTINES.

“BIN”
53EB

00H

Storage for YEAR or SECOND.

53EC

00H

Storage for DAY or MINUTE.

53ED

00H

Storage for MONTH or HOUR.

53EEH – Subroutine within the DATE COMMAND to decode the date and validate for proper delimeters.

“CONV1”
53EE

LD DE,BIN + 2

LET Register Pair DE = 53EDH (i.e., the end of the DATE storage area, since this routine is parsing the numbers backwards).

53F1

LD B,03H

LET Register B = 03H, to signify 3 bytes.

“L6OP1”
53F3

PUSH DE

Save Register DE (i.e., the DATE storage area) to the top of the stack.

53F4

CALL DECBIN
[5403H]

GOSUB to 5403H to decode a two digit number pointed to by Register Pair HL; results in Register A.

53F7

POP DE

Restore the DATE storage area from the top of the STACK into Register Pair DE .

53F8

RET NZ

If the NZ FLAG (Not Zero) is set then that CALL exited with an error, so RETurn to the caller.

53F9

LD (DE),A

Store the value held in Register A (i.e., the decoded number) into the memory location pointed to by Register Pair DE.

53FA

DEC DE

DECrement the value stored in Register Pair DE by 1 to point to the next entry in the DATE STORAGE AREA.

53FB

DEC B

DECrement the value stored in Register B (i.e., a counter) by 1.

53FC

RET Z

If the Z FLAG (Zero) is set then we have processed all 3 elements of a date, so RETurn to the caller.

53FD

LD A,(HL)

Fetch the value stored at memory location pointed to by Register Pair HL (i.e., the command line) and put it into Register A.

53FE

INC HL

Bump the value stored in Register Pair HL by 1 to point to the next character in the command line.

53FF

CP C

Compare the value held in Register A (i.e., a character in the command line) against the value held in Register C (i.e., a / delimeter). Results: If Register A equals /, the Z FLAG is set; otherwise the NZ FLAG is set.

5400

JR Z,L6OP1
[53F3H]

If we properly had a / here, then the Z FLAG (Zero) is set, JUMP to 53F3H to keep parsing the 3 date elements.

5402

RET

RETurn to the caller with NZ set to signify an error.

5403H – Subroutine within the DATE COMMAND to decode a two digit number pointed to by Register Pair HL; results in Register A.

“DECBIN”
5403

CALL 541AH
[541AH]

GOSUB to 541AH to convert a COMMAND LINE byte pair to decimal.

5406

JR NC,RET1
[5418H]

If the NC FLAG (No Carry) is set then that CALL exited with an ERROR so JUMP to 5418H.

5408

LD E,A

LET Register E = Register A (i.e., the returned value).

5409

RLCA

Let A = A * 2.

540A

RLCA

Let A = A * 2 (so A is now 4 times the original value).

540B

ADD A,E

ADD the value held in Register E to Register A (so A is now 5 times the original value).

540C

RLCA

Let A = A * 2 (so A is now 10 times the original value).

540D

LD E,A

LET Register E = Register A (i.e., the returned value, but now in the tens place).

540E

CALL DECCHK
[541AH]

GOSUB to 541AH to get the parameter digit value.

5411

JR NC,RET1
[5418H]

If the NC FLAG (No Carry) is set then that CALL exited with an ERROR so JUMP to 5418H.

5413

ADD A,E

ADD the value held in Register E (i.e., the first number shifted to the tens place) to Register A (i.e., the second number we just processed).

5414

LD E,A

LET Register E = Register A (i.e., the two numbers combined).

5415

XOR A

Set Register A to ZERO and clear all Flags.

5416

LD A,E

LET Register A = Register E (i.e., the two numbers combined).

5417

RET

RETurn to the caller.

5418H – Subroutine within the DATE COMMAND to exit with the error status set.

“RET1”
5418

OR A

Set FLAGS based on the contents of Register A.

5419

RET

RETurn to the caller.

541AH – Subroutine within the DATE COMMAND to convert a COMMAND LINE byte pair to decimal. Exits with NC FLAG set if there is an error.

“DECCHK”
541A

LD A,(HL)

Fetch the value stored at memory location pointed to by Register Pair HL (i.e., the parameter byte we want to decode) and put it into Register A.

541B

INC HL

Bump the value stored in Register Pair HL by 1 to point to the next parameter byte.

541C

SUB 30H

541E

CCF

Invert the state of the CARRY FLAG.

541F

RET NC

If the NC FLAG (No Carry) is set, RETurn to the caller.

5420

CP 0AH

Compare the value held in Register A against 0AH (Decimal: 10) as a double-check. Results:

If Register A equals 10, the Z FLAG is set.
If A < 10 (which is good), the CARRY FLAG will be set.
if A >= 10, which is bad, the NO CARRY FLAG will be set.

5422

RET

RETurn to the caller.

5423H – LIB Library Command – Function 23

“LIB”
5423

LD HL,LIBCOM

LET Register Pair HL = 50C9H which is the OVERLAY 1 COMMAND TABLE.

“L6OP4”
5426

LD C,08H

LET Register C = 08H, because there are 8 columns per row.

“L6OP3”
5428

LD B,06H

LET Register B = 06H, because there are 6 characters per library command.

“L6OP2”
542A

LD A,(HL)

Fetch the value stored at memory location pointed to by Register Pair HL (i.e., the OVERLAY 1 COMMAND TABLE) and put it into Register A.

542B

INC HL

Bump the value stored in Register Pair HL by 1 to point to the next character of that command table.

542C

CALL DSP
[0033H]

GOSUB to 0033H.
NOTE: 0033H is the Model III ROM character print routine; displays the character held in Register A at the current cursor position.

542F

DJNZ L6OP2

LOOP back to 542AH until Register B is ZERO, meaning a full command has been displayed.

5431

LD A,(CURSOR)

Fetch the value stored at memory location 4020H and put it into Register A.
NOTE: 4020H is the storage location for the CURSOR POSITION ON SCREEN.

5434

AND 3FH

MASK the value of Register A against 3FH to mask for an END OF DISPLAY LINE computation.

5436

CP 38H

Compare the value held in Register A against 38H to see if we have reached the end of a line on the screen. Results: if A >= 38H, the NO CARRY FLAG will be set.

5438

JR NC,LL6OP2
[5442H]

If the NC FLAG (No Carry) is set then we are at the end of a display line, so JUMP to 5442H to skip the spacing between the library commands.

543A

LD A,20H

LET Register A = 20H (ASCII: SPACE) because we need to put two spaces between library commands.

543C

CALL DSP
[0033H]

GOSUB to 0033H.
NOTE: 0033H is the Model III ROM character print routine; displays the character held in Register A at the current cursor position.

543F

CALL DSP
[0033H]

GOSUB to 0033H.
NOTE: 0033H is the Model III ROM character print routine; displays the character held in Register A at the current cursor position.

“LL6OP2”
5442
5443

INC HL
INC HL

Bump the value stored in Register Pair HL by 2 to point to the next entry in the OVERLAY 1 COMMAND TABLE.

5444

LD A,(HL)

Fetch the value stored at memory location pointed to by Register Pair HL (i.e., the next command in the OVERLAY 1 COMMAND TABLE) and put it into Register A.

5445

OR A

Since a LD command does not set any FLAGS, Set FLAGS based on the contents of Register A.

5446

JR Z,S6CR
[5450H]

If the Z FLAG (Zero) is set then we have hit the END of the OVERLAY 1 COMMAND TABLE so JUMP to 5450H to finish up.

5448

DEC C

DECrement the value stored in Register C by 1, since C is counting down the number of columns on a display.

5449

JR NZ,L6OP3
[5428H]

If the NZ FLAG (Not Zero) is set, JUMP to 5428H to process the next library command.

544B

CALL S6CR
[5450H]

GOSUB to 5450H to move to a new line on the screen.

544E

JR L6OP4
[5426H]

JUMP to 5426H to keep displaying.

5450H – Continuation of the LIBRARY COMMAND; jumped to if we have finished displaying the OVERLAY 1 COMMAND TABLE.

“S6CR”
5450

LD A,0DH

LET Register A = 0DH (ASCII: CARRIAGE RETURN.

5452

JP DSP
[0033H]

JUMP to 0033H.
NOTE: 0033H is the Model III ROM character print routine; displays the character held in Register A at the current cursor position.

5455H – PROT Library Command – Function 29

“S6PROT”
5455

LD BC,0000H

LET Register Pair BC = 0000H so that we can turn off a bunch of options.

5458

LD (PW),BC

Store the value held in Register BC (i.e., 0000H) into the memory location 54A3H (which is in the middle of an LD DE,nnnnH OPCODE).

545C

LD (LOCK),BC

Store the value held in Register BC (i.e., 0000H) into the memory location 54C3H (which is in the middle of a LD DE,nnnnH OPCODE).

5460

LD A,(HL)

Fetch the value stored at memory location pointed to by Register Pair HL (i.e., the command line which was passed to this overlay) and put it into Register A.

5461

CP 3AH

Compare the value held in Register A against 3AH (ASCII: :) to check for a DRIVE NUMBER. Results: If Register A equals :, the Z FLAG is set; otherwise the NZ FLAG is set.

5463

JR NZ,NODRV3
[546BH]

If the character retrieved from the command line is not a :, then the NZ FLAG (Not Zero) is set, so JUMP to 546BH.

5465

INC HL

If we are here, we are expecing a DRIVE NUMBER to be the next character, so bump the value stored in Register Pair HL (i.e., the command line which was passed to this overlay) by 1.

5466

LD A,(HL)

Fetch the value stored at memory location pointed to by Register Pair HL, which we hope to be a drive number, and put it into Register A.

5467

SUB 30H

5469

LD C,A

LET Register C = Register A (i.e., the decimal equivalent of a drive number from the command line).

546A

INC HL

Bump the value stored in Register Pair HL (i.e., the command line which was passed to this overlay) by 1.

“NODRV3”
546B

LD A,C

LET Register A = Register C (i.e., the decimal equivalent of a drive number from the command line).

546C

LD (DRV3),A

Store the value held in Register A (i.e., the decimal equivalent of a drive number from the command line) into the memory location 548FH (which is in the middle of a LD C,nn OPCODE).

546F

LD DE,SWITCH5

LET Register Pair DE = 554EH to point to the PARAMETER TABLE.

5472

CALL SWITCH
[4454H]

GOSUB to 4454H.
NOTE: 4454H is the DOS PARAMETER STRING PARSE routine. It decodes DOS LIBRARY parameters.

5475

JP NZ,ERR2
[5214H]

If the NZ FLAG (Not Zero) is set then the prior CALL exited with an error, so JUMP to 5214H.

5478

LD A,(PW)

We need to check to see if either of the valid parameters were specified so first fetch the value stored at memory location 54A3H (which is in the middle of an LD DE,nnnnH OPCODE, but is doubling as storage as well) and put it into Register A.

547B

LD HL,LOCK

LET Register Pair HL = 54C3H (which an LD DE,nnnnH OPCODE that is doubling as storage as well.

547E

OR (HL)

OR the value stored at (HL) against Register A to see if those 2 locations match. The results are stored in Register A.

547F

JP Z,ERR3
[5218H]

If the Z FLAG (Zero) is set then we have a problem so JUMP to 5218H.

5482

LD HL,OLDMAS

LET Register Pair HL = 5526H to point to the message storage area for “MASTER PASSWORD?“.

5485

CALL PRINT
[021BH]

GOSUB to 021BH.
NOTE: 021BH will display the character at (HL) until a 03H is found.

5488

CALL MASINP
[551AH]

GOSUB to 551AH to get a response from the user to that prompt and encode it; results in HL.

548B

LD (INPPAS),HL

Store the value held in Register HL (i.e., the hashed password) into the memory location 549AH.

548E

LD C,DRV3

LET Register C = nnH, a value which is placed in 458FH elsewhere.

5490

CALL RDGAT
[4A93H]

GOSUB to 4A93H.
NOTE: 4A93H is the SYS00/SYS routine to READ THE GAT sector into RAM (Buffer at 4D00H).

5493

JP NZ,ERR
[6132H]

If the NZ FLAG (Not Zero) is set then the CALL to READ THE GAT SECTOR has resulted in an error; so JUMP to 6132H.

5496

LD HL,(BUFF2 + DPASS)

Fetch the value stored at memory location 4DCEH (i.e., the hashed master password as stored in the GAT SECTOR) and put it into Register HL.

5499

LD DE,INPPASS

LET Register Pair DE = nnnnH, a value which is placed in 549AH-549BH elsewhere.

549C

OR A

Set FLAGS based on the contents of Register A.

549D

SBC HL,DE

Subtracts the value stored in Register Pair DE (i.e., the hashed version of the master password the user just entered) and the carry flag from the value stored in Register Pair HL (i.e., the hashed master password as stored in the GAT SECTOR).

549F

JP NZ,ERR4
[5238H]

If the NZ FLAG (Not Zero) is set then those two passwords did NOT match, so JUMP to 5238H.

54A2

LD DE,PW

LET Register Pair DE = nnnnH, a value which is placed in 54A3H-54A4H elsewhere.

54A6
54A5

LD A,D
OR E

Since the Z-80 cannot test Register Pair DE against zero, the common trick is to set Register A to equal to Register D, and then OR A against Register E. Only if both Register D and Register E were zero can the Z FLAG be set.

54A7

JR Z,NOPW
[54BFH]

If the Z FLAG (Zero) is set then we have NOT been asked to change the password, so JUMP to 54BFH.

54A9

LD HL,NEWPAS

LET Register Pair HL = 5538H to point to the message storage area for “NEW MASTER PASSWORD?“.

54AC

CALL PRINT
[021BH]

GOSUB to 021BH.
NOTE: 021BH will display the character at (HL) until a 03H is found.

54AF

CALL MASINP
[551AH]

GOSUB to 551AH to get a response from the user to that prompt and encode it; results in HL.

“PROTOK”
54B2

LD (BUFF2 + DPASS),HL

Store the value held in Register HL into the memory location 4DCEH, which is the location in the GAT SECTOR in RAM for the MASTER PASSWORD.

54B5

LD A,(DRV3)

Fetch the value stored at memory location 548FH (i.e., the drive spec) and put it into Register A.

54B8

LD C,A

Since most DISK I/O routines expect the drive letter to be in Register C, LET Register C = Register A (i.e., the drive spec).

54B9

CALL WRGAT
[4A9BH]

GOSUB to 4A9BH.
NOTE: 4A9BH is the SYS00/SYS routine to to write the GAT sector from RAM to diskette.

54BC

JP NZ,ERR
[6132H]

If the NZ FLAG (Not Zero) is set then the routine to WRITE THE GAT SECTOR FROM RAM TO DISK returned an error, so JUMP to 6132H.

“NOPW”
54BF

LD HL,(BUFF2 + DPASS)

Fetch the value stored at memory location 4DCEH (i.e., the hashed master password as stored in the GAT SECTOR) and put it into Register HL.

54C2

LD DE,LOCK

LET Register Pair DE = nnnnH, a value stored in memory locations 54C3H-54C4 elsewhere in this overlay.

54C6
54C5

LD A,D
OR E

54C7

RET Z

If the Z FLAG (Zero) is set, then DE was zero meaning that we do not need to lock all the files on the diskette, so RETurn to the caller.

“NOLOCK”
54C8

LD (PASSW),HL

Store the value held in Register HL (i..e, the hashed master password) into the memory location 54F2H.

54CB

LD A,(DRV3)

Fetch the value stored at memory location 548FH (i.e., the drive number) and put it into Register A.

54CE

LD C,A

Since most DISK I/O routines expect the drive letter to be in Register C, LET Register C = Register A (i.e., the drive spec).

54CF

CALL TRKGET
[4B3EH]

GOSUB to 4B3EH to prepare the diskette for a DIRECTORY READ.

54D2

LD E,DIRSEC

LET Register E = 03H to signify that we want directory sector 3.

“L6OP36”
54D4

LD HL,BUFF1

LET Register Pair HL = 4300H to set up for a RAM buffer.

54D7

LD (BUFSAV),HL

Store the value held in Register HL (i.e., the RAM buffer pointer) into the memory location 54FDH.

54DA

CALL SREAD
[4B0DH]

GOSUB to 4B0DH to READ the directory sector held in Register E from the Drive held in Register C into a memory buffer pointed to by Register Pair HL.

54DD

JP NZ,ERR
[6132H]

If the NZ FLAG (Not Zero) is set then the CALL to READ THE DIRECTOR SECTOR returned an error; so JUMP to 6132H.

“L6OP35”
54E0

LD A,(HL)

Fetch the value stored at memory location pointed to by Register Pair HL (i.e., a byte of the directory sector) and put it into Register A.

54E1

OR A

Since a LD command does not set any FLAGS, Set FLAGS based on the contents of Register A.

54E2

JR Z,HASPAS
[54FCH]

If the Z FLAG (Zero) is set, then the first byte in the directory sector is ZERO, meaning file is NOT in use. If that’s the case, JUMP to 54FCH.

54E4

AND PNOACC

MASK the value of Register A against 07H (0000 0111). This has the effect of turning off bits 7, 6, 5, 4, 3, leaving only bits 2, 1, 0, which are the SECURITY LEVEL active.

54E6

JR NZ,HASPAS
[54FCH]

If the NZ FLAG (Not Zero) is set then we have a SYSTEM FILE here, so JUMP to 54FCH.

54E8

LD A,(HL)

Fetch the value stored at memory location pointed to by Register Pair HL (i.e., the FILE TYPE byte of the DIRECTORY SECTOR in RAM) and put it into Register A.

54E9

OR PEXEC

OR Register A against 06H (0000 0110). This has the effect of turning on bits 2 and 1 to signify KILL access.

54EB

LD (HL),A

Store the value held in Register A (i.e., the FILE TYPE byte with KILL ACCESS enabled) into the memory location (i.e., the FILE TYPE byte of the DIRECTORY SECTOR in RAM) pointed to by Register Pair HL.

54ED
54EC
54EF

LD A,L
ADD A,DUPD
LD L,A

LET Register L = Register L + 10H. HL will now point to the PASSWORD in the DIRECTORY SECTOR in RAM.

54F0

PUSH DE

Save Register DE to the top of the stack.

54F1

LD DE,PASSW

LET Register Pair DE = nnnnH, a value stored in memory locations 54F2H-54F3H elsewhere in this overlay.

The next few instructions put the password hash stored in Register Pair DE into the UPDATE and ACCESS password slots of the DIRECTORY SECTOR in RAM.

54F4

LD (HL),E

Store the value held in Register E into the memory location pointed to by Register Pair HL.

54F5

INC HL

Bump the value stored in Register Pair HL by 1.

54F6

LD (HL),D

Store the value held in Register D into the memory location pointed to by Register Pair HL.

54F7

INC L

Bump the value stored in Register L by 1.

54F8

LD (HL),E

Store the value held in Register E into the memory location pointed to by Register Pair HL.

54F9

INC HL

Bump the value stored in Register Pair HL by 1.

54FA

LD (HL),D

Store the value held in Register D into the memory location pointed to by Register Pair HL.

54FB

POP DE

Restore Register Pair DE from the top of the STACK.

“HASPASS”
54FC

LD HL,BUFSAV

LET Register Pair HL = nnnnH, a value stored in memory locations 54FDH-54FEH elsewhere in this overlay, and is meant to be the buffer pointer.

5500
54FF
5502

LD A,L
ADD A,SIZDIR
LD L,A

LET Register L = Register L + 30H. HL will now point to the next directory entry in the DIRECTORY SECTOR in RAM.

5503

LD (BUFSAV),HL

Store the value held in Register HL (i.e., the buffer pointer) into the memory location 54FDH.

5506

CP 0F0H

Compare the value held in Register A against 0F0H to see if we are at the end of a sector yet. Results:

If Register A equals 0F0H, the Z FLAG is set.
If A < 0F0H, the CARRY FLAG will be set.
if A >= 0F0H, the NO CARRY FLAG will be set.

5508

JR C,L6OP35
[54E0H]

If the C FLAG (Carry) is set, then we are NOT at the end of the sector, so LOOP BACK to 54E0H.

550A

LD HL,BUFF1

LET Register Pair HL = 4300H, which is the RAM Buffer.

550D

CALL XWRITE
[45F7H]

GOSUB to 45F7H to write the RAM BUFFER pointed to by Register Pair HL to the directory sector.

5510

JP NZ,ERR
[6132H]

If the NZ FLAG (Not Zero) is set then the prior subroutine to write the RAM BUFFER to diskette returned an error, so JUMP to 6132H.

5513

INC E

Bump the value stored in Register E by 1 so as to point to the next sector of the directory.

5514

LD A,E

LET Register A = Register E for purposes of checking that value.

5515

CP TRACK + 1

Compare the value held in Register A against 13H (Decimal: 19). Results:

If Register A equals 13H, the Z FLAG is set.
If A < 13H, the CARRY FLAG will be set.
if A >= 13H, the NO CARRY FLAG will be set.

5517

JR C,L6OP36
[54D4H]

If the C FLAG (Carry) is set then we have not yet reached the end of the directory, so LOOP BACK to 54D4H.

5519

RET

RETurn to the caller.

551AH – SUBroutine as part of the PROT routine.

“MASINP”
551A

LD HL,BUFF1

LET Register Pair HL = 4300H to as to point to the RAM BUFFER.

551D

LD B,08H

LET Register B = 08H, signifying 8 characters to be read.

551F

CALL KEYN
[0040H]

GOSUB to 0040H.
NOTE: 0040H is the Model III ROM routine to get a full line from the keyboard. In this routine, a line is terminated by a carriage return or BREAK, and characters typed are echoed to the display. On entry, B must be the maximum length of line to be accepted and (HL) must be the storage buffer which should be set to B+1. On Exit, CARRY will be set if the BREAK key was hit, Register B will contain the number of characters entered, and (HL) will contain the line from the keyboard followed by the terminating character. Register Pair DE is altered in this routine.

5522

CALL TRAP
[555FH]

GOSUB to 555FH to to encode a password into Register Pair HL.

5525

RET

RETurn to the caller.

5526H – MESSAGE STORAGE AREA for the PROT command.

“OLDMAS”
5526

DEFM …

“MASTER PASSWORD?“.

“NEWPAS”
5538

DEFM …

“NEW MASTER PASSWORD?“.

554EH – PARAMETER STORAGE AREA for the PROT command.

“SWTCH5”
554E

DEFM …

“PW “. Note: The FLAG for this is at 54A3H.

5546

DEFM …

“LOCK “. Note: The FLAG for this is at 54CEH..

555E

DEFB 00H

Terminator.

555FH – SUBROUTINE from the PROT library command to encode a password.

“TRAP”
555F

EX DE,HL

EXchange the value stored in Register Pair HL (i.e., the end of the password entered by the user followed by the terminating character) with the value stored in Register Pair DE (i.e., the password entered by the user followed by the terminating character).

5560

LD H,D

LET Register H = Register D.

5561

LD A,B

LET Register A = Register B (i.e., the length of the password which was entered).

5562

ADD A,E

LET Register A = Register A + Register E.

5563

LD L,A

LET Register L = Register A.

5564

LD A,08H

LET Register A = 08H, which is the length of a full size password.

5566

SUB B

LET Register A = Register A – Register B.

5567

JR Z,NOSPC
[556FH]

If the the length of the password entered is equal to the maximum length of password then the Z FLAG (Zero) is set, JUMP to 556FH.

5569

LD B,A

LET Register B = Register A (i.e., the number of blanks at the end of the password), in preparation for a DJNZ loop to fill in that number of characters with spaces.

“FILSPC”
556A

LD (HL),20H

Store the a SPACE into the memory location pointed to by Register Pair HL.

556C

INC HL

INCrement the value stored in Register Pair HL by 1 to point to the next character in the user entered password.

556D

DJNZ FILSPC
[556AH]

LOOP back to 556AH, reducing Register B each time, and continue to LOOP until Register B has been reduced to ZERO, in which case, continue with the next instruction.

“NOSPC”
556F

LD HL,0FFFFH

LET Register Pair HL = 0FFFFH (Decimal: -1).

5572

LD B,08H

LET Register B = 08H, which is the length of a full size password.

5574
5575
5577

LD A,E
ADD A,07H
LD E,A

LET Register E = Register E + 07H, which means DE is now the last letter in the password.

5578

JR NC,SETTD2
[557BH]

Since we only did math on E instead of Register Pair DE, there is a risk that Register E will have spilled over. If that happened, then the C FLAG will be sent and we will need to increase D. If, however, the NC FLAG (No Carry) is set, we don’t need to do that, so skip that by JUMPing to 557BH.

557A

INC D

INCrement the value stored in Register D by 1 since the math on Register E produced a carry.

“SETTD2”
557B

LD A,(DE)

Fetch the value stored at memory location pointed to by Register Pair DE (i.e., a character in the password) and put it into Register A.

557C

PUSH DE

Save Register Pair DE (i.e., the pointer to the currently processed character in the user entered password) to the top of the stack.

557D

LD D,A

LET Register D = Register A (i.e., the character pointed to by register pair (DE)).

557E

LD E,H

LET Register E = Register H (i.e., the MSB of the password).

557F

LD A,L

LET Register A = Register L (i.e., the LSB of the password).

5580

AND 07H

MASK the value of Register A against 07H (0000 0111). This has the effect of turning off bits 7, 6, 5, 4, 3, leaving only bits 2, 1, 0 active.

5583
5582
5584

RRCA
RRCA
RRCA

Rotate the remaining bits (2-1-0) into bits 7-6-5 by doing three RRCA’s (which rotates the contents of A right one bit position; so that, for example, the contents of bit 0 are copied bit 7).

5585

XOR L

eXclusive OR Register L against Register A, to combine with the LSB. The results are stored in Register A.

5586

LD L,A

LET Register L = Register A (i.e., the masked, rotated, XOR’d LSB of the password).

5587

LD H,00H

LET Register H = 00H, in preparation for math.

5589

SBC HL,DE

LET HL = A – DE.

558C
558B

ADD HL,HL
ADD HL,HL

LET Register Pair HL = Register Pair HL * 4.

558E
558D

XOR H
XOR D

eXclusive OR Register H and then Register D against Register. This leaves the new MSB in Register A.

558F

LD D,A

LET Register D = Register A (i.e., the MSB of the password).

5590

LD A,L

LET Register A = Register L (i.e., the LSB of the password).

5591

ADD HL,HL

LET Register Pair HL = Register Pair HL * 2.

5592

XOR H

eXclusive OR Register H against Register A to combine with the MSB.

5593

XOR E

eXclusive OR Register E against Register A to further combine with the LSB of Register Pair DE.

5594

LD E,A

LET Register E = Register A (i.e., the new LSB of DE).

5595

EX DE,HL

EXchange the value stored in Register Pair HL with the value stored in Register Pair DE (i.e., the new password).

5596

POP DE

Put the value held at the top of the STACK (i.e., the pointer to the character in the password string which was just processed) into Restore Register Pair DE, and then remove the entry from the stack.

5597

DEC DE

DECrement the value stored in Register Pair DE by 1 so as to move the pointer to the previous character in the password string.

5598

DJNZ SETTD2
[557BH]

Keep processing 8 characters of the password by LOOPing back to 557BH, reducing Register B each time, and continue to LOOP until Register B has been reduced to ZERO, in which case, continue with the next instruction.

559B
559A

LD A,H
OR L

Since the Z-80 cannot test Register Pair HL against zero, the common trick is to set Register A to equal to Register H, and then OR A against Register L. Only if both Register H and Register L were zero can the Z FLAG be set.

559C

RET NZ

If the password is NOT blank (i.e., Register Pair HL does not equal 0), then the NZ FLAG (Not Zero) is set, and RETurn to the caller.

559D

INC L

If we are here, then HL=0, which is bad. Since we can’t have a 0 there, INCrement the value stored in Register L by 1.

559E

RET

RETurn to the caller.

559FH – RENAME Library Command

“RENAME”
559F

CALL GETSYN
[623AH]

GOSUB to 623AH to isolate and validate the FILESPEC from the command line via an OVERLAY call to ROUTINE 4 of OVERLAY 1.

55A2

JP NZ,ERR3
[5218H]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned because of an ERROR, JUMP to 5218H.

55A5

PUSH HL

Save Register Pair HL (i.e., the command line address) to the top of the stack.

55A6

PUSH DE

Save Register Pair DE (i.e., the DCB address) to the top of the stack.

55A7

LD HL,NAME1

LET Register Pair HL = 5666H to point to the filename.

55AA

LD DE,S6DCB1

LET Register Pair DE = 6280H to point to the print buffer.

55AD

CALL MOVNAM
[563DH]

GOSUB to 563DH to copy the contents of (DE) to (HL) until a control character is reached, at which point JUMP to 5647.

55B0

POP DE

Put the value held at the top of the STACK (i.e., the DCB address) into Restore Register Pair DE, and then remove the entry from the stack.

55B1

POP HL

Put the value held at the top of the STACK (i.e., the command line address) into Restore Register Pair HL, and then remove the entry from the stack.

55B2

CALL OPEN
[4424H]

GOSUB to 4424H which is the SYS00/SYS routine to OPEN A DISK FILE for use. This RST 28H’s with a value of 92H so as to call ROUTINE 1 in OVERLAY 3.

55B5

JP NZ,ERR
[6132H]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned because of an ERROR, JUMP to 6132H.

55B8

LD DE,S6DCB2

LET Register Pair DE = 62B2H to point to the second filename DCB.

55BB

CALL SYNTAX
[441CH]

GOSUB to 441CH.

55BE

JP NZ,ERR3
[5218H]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned because of an ERROR, JUMP to 5218H.

55C1

LD A,(S6DCB1 + PROT)

Fetch the value stored at memory location 6281H (i.e., the access level byte in the first file’s DCB) and put it into Register A.

55C4

AND 07H

MASK the value of Register A against 07H (0000 0111) to isolate the access level. This has the effect of turning off bits 7, 6, 5, 4, 3, leaving only bits 2, 1, 0 active.

55C6

CP 03H

Compare the value held in Register A against 03H, which would be the right to RENAME or higher. Results:

If Register A equals 03H, the Z FLAG is set.
If A < 03H, the CARRY FLAG will be set.
if A >= 03H, the NO CARRY FLAG will be set.

55C8

LD A,EFAD

LET Register A = 19H, to signify a File Access Denied Due to To Password Protection error.

55CA

JP NC,ERR
[6132H]

If the access level was >= 03H, the NC FLAG (No Carry) will be set, JUMP away to 6132H.

55CD

LD HL,S6DCB2

LET Register Pair HL = 62B2H so as to point to the second filename.

“L6OP34”
55D0

LD A,(HL)

Fetch the value stored at memory location pointed to by Register Pair HL and put it into Register A.

55D1

CP 3AH

Compare the value held in Register A against 3AH (ASCII: :) to test for a drive number. Results: If Register A equals :, the Z FLAG is set; otherwise the NZ FLAG is set.

55D3

JP Z,ERR2
[5214H]

If that character was a :, which is not a good thing, then the Z FLAG (Zero) is set, so JUMP to 5214H.

55D6

CP 20H

Compare the value held in Register A against 20H (ASCII: SPACE). Results:

If Register A equals SPACE, the Z FLAG is set.
If A < SPACE, the CARRY FLAG will be set.
if A >= SPACE, the NO CARRY FLAG will be set.

55D8

INC HL

INCrement the value stored in Register Pair HL by 1 so as to point to the next characeter in the second filename.

55D9

JR NC,L6OP34
[55D0H]

If the character was a A >= SPACE, then the NC FLAG (No Carry) is set, so LOOP back to 55D0H to keep parsing the 2nd filename.

55DB

DEC HL

DECrement the value stored in Register Pair HL by 1 so that HL will now point to the end of the filename.

“CONTE”
55DC

LD (HL),3AH

Store a 20H (ASCII: :) into the memory location pointed to by Register Pair HL (i.e., the end of the filename).

55DE

INC HL

INCrement the value stored in Register Pair HL by 1 to point to the next character of the filename.

55DF

LD A,(S6DCB1 + DRVNUM)

Fetch the value stored at memory location 6286H (i.e., the drive number, in decimal) and put it into Register A.

55E2

ADD A,30H

LET Register A = Register A + 30H. Note: Adding 30H to from Register A will convert decimal number 0-9 into its ASCII equivalent (i.e., 6 + 30H = 36H, which, in ASCII, is 6.

55E4

LD (HL),A

Store the value held in Register A (i.e., the ASCII equivalent of the drive number) into the memory location pointed to by Register Pair HL (i.e, the end of the filename).

55E5

INC HL

INCrement the value stored in Register Pair HL by 1 to point to the next character of the filename.

55E6

LD (HL),03H

Store the value held in Register 03H, which is a standard terminator, into the memory location pointed to by Register Pair HL (i.e., the end of the filename).

55E8

LD DE,S6DCB2

LET Register Pair DE = 62B2H to point to the SECOND filename.

55EB

PUSH HL

Save Register Pair HL (i.e., the pointer to the last character of the first filename) to the top of the stack.

55EC

PUSH DE

Save Register Pair DE (i.e., the pointer to the second filename) to the top of the stack.

55ED

LD HL,NAME2

LET Register Pair HL = 5676H to point to the second filename.

55F0

LD DE,S6DCB2

LET Register Pair DE = 62B2H to point to the print buffer.

55F3

CALL MOVNAM
[563DH]

GOSUB to 563DH to copy the contents of (DE) to (HL) until a control character is reached, at which point JUMP to 5647.

55F6

POP DE

Put the value held at the top of the STACK (i.e., the pointer to the second filename) into Restore Register Pair DE, and then remove the entry from the stack.

55F7

POP HL

Put the value held at the top of the STACK (i.e., the pointer to the last character of the first filename) into Restore Register Pair HL, and then remove the entry from the stack.

55F8

CALL OPEN
[4424H]

GOSUB to 4424H
NOTE: 4424H is the SYS00/SYS routine to OPEN A DISK FILE for use. This RST 28H’s with a value of 92H so as to call ROUTINE 1 in OVERLAY 3.

55FB

JP Z,ERR1
[521CH]

If the Z FLAG (Zero) is set then the second filename has been found, so JUMP to 521CH.

55FE

CP EFNF

Compare the value held in Register A (which returned from 521CH) against 18H (i.e., a FILE NOT FOUND ERROR). Results: If Register A equals 18H, the Z FLAG is set; otherwise the NZ FLAG is set.

5600

JP NZ,ERR
[6132H]

If the NZ FLAG (Not Zero) is set, then we didn’t get a FILE NOT FOUND error, so JUMP to 6132H.

5603

CALL DSPNAM
[564AH]

GOSUB to 564AH to Display a Verification Message of “filename1 —-> filename2”.

5606

LD BC,(S6DCB1 + DRVNUM)

Fetch the value stored at memory location 6286H (i.e., the drivespec) and put it into Register BC.

560A

PUSH BC

Save Register Pair BC (i.e., the the drive number and file number) to the top of the stack.

560B

CALL RDDIR
[4A67H]

GOSUB to 4A67H.
NOTE: 4A67H is the SYS00/SYS routine to read the directory entry into RAM (Buffer at 4300H).

560E

JP NZ,ERR
[6132H]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned because of an ERROR, JUMP to 6132H.

The next 4 instructions just set DE = HL + 5, which is the the pointer to the FILENAME in the directory entry.

5611

LD D,H

LET Register D = Register H, so Register D (MSB of DE) will match H (MSB of HL).

5612

LD A,L

LET Register A = Register L, so Register A = the LSB of HL.

5613

ADD A,DNAME

LET Register A = Register A + 05H, so Register A = the LSB of HL + 5.

5615

LD E,A

LET Register E = Register A (i.e., the LSB of HL + 5). Register Pair DE is now pointing to the the FILENAME in the directory entry.

5616

LD HL,NAME

LET Register Pair HL = 5141H, which is a temporary memory storage location for the filename.

5619

LD BC,000BH

LET Register Pair BC = 000BH (Decimal: 11) to set up for a move of 11 bytes.

561C

LDIR

Use LDIR to move the filename to 5141H. LDIR transfers a byte of data from the memory location pointed to by HL to the memory location pointed to by DE. Then HL and DE are incremented and BC is decremented. If BC is not zero, this operation is repeated. Interrupts can trigger while this instruction is processing.

561E

POP BC

Put the value held at the top of the STACK (i.e., the drive number and file number) into Register Pair BC, and then remove the entry from the stack.

561F

CALL WRDIR
[4A7BH]

GOSUB to 4A7BH.
NOTE: 4A7BH is the SYS00/SYS routine to to write the directory entry from the copy in RAM to the diskette.

5622

JP NZ,ERR
[6132H]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned because of an ERROR, JUMP to 6132H.

5625

CALL RHDIT
[4ABAH]

GOSUB to 4ABAH.
NOTE: 4ABAH is the SYS00/SYS routine to read the HIT sector into RAM.

5628

JP NZ,ERR
[6132H]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned because of an ERROR, JUMP to 6132H.

562B

LD D,H

LET Register D = Register H, so Register D (MSB of DE) will match H (MSB of HL).

562C

LD E,B

LET Register E = Register B (i.e., the file number). With this Register Pair DE now points to the HASH TABLE ENTRY for the filename.

562D

PUSH BC

Save Register Pair BC (i.e., the drive number and file number) to the top of the stack.

562E

LD HL,NAME

LET Register Pair HL = 5141H, which is a temporary memory storage location for the filename.

5631

CALL HASH
[50E7H]

GOSUB to 50E7H to hash the filename pointed to by Register Pair HL; results in Register A.

5634

POP BC

Put the value held at the top of the STACK (i.e., the drive number and file number) into Restore Register Pair BC, and then remove the entry from the stack.

5635

LD (DE),A

Store the value held in Register A (i.e., the hashed filename) into the memory location pointed to by Register Pair DE.

5636

CALL WRHIT
[4AC2H]

GOSUB to 4AC2H.
NOTE: 4AC2H is the SYS00/SYS routine to write the HIT sector from RAM to diskette.

5639

JP NZ,ERR
[6132H]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned because of an ERROR, JUMP to 6132H.

563C

RET

RETurn to the caller.

563DH – Copy the contents of (DE) to (HL) until a control character is reached, at which point JUMP to 5647.

“MOVNAM”
563D

LD A,(DE)

Fetch the value stored at memory location (i.e., a character) pointed to by Register Pair DE and put it into Register A.

563E

CP 20H

Compare the value held in Register A against 20H. If Register A < 20H, the CARRY FLAG will be set.

5640

JR C,MOVNA1
[5647H]

If Register A < 20H, then the C FLAG (Carry) is set and we have a CONTROL CHARACTER, so JUMP to 5647H to add a 03H terminator and RETURN.

5642

LD (HL),A

Store the value held in Register A (i.e., a character which we now know is at least greater than 20H) into the memory location pointed to by Register Pair HL.

5643

INC HL

INCrement the value stored in Register Pair HL by 1 for the next character to test and move from (DE) to (HL).

5644

INC DE

INCrement the value stored in Register Pair DE by 1 for the next character to test and move from (DE) to (HL).

5645

JR MOVNAM
[563DH]

LOOP back to the top of this routine at 563DH.

5647H – Continuation of the 563DH routine; add a 03H Terminator and RETurn.

“MOVNA1”
5647

LD (HL),03H

Store the value held in Register 03H into the memory location pointed to by Register Pair HL.

5649

RET

RETurn to the caller.

564AH – SUBROUTINE called from 5603H to Display a Verification Message of “filename1 —-> filename2”.

“DSPNAM”
564A

PUSH BC

Save Register Pair BC to the top of the stack.

564B

PUSH DE

Save Register Pair DE to the top of the stack.

564C

PUSH HL

Save Register Pair HL to the top of the stack.

564D

LD HL,NAME1

LET Register Pair HL = 5666H to point to FILENAME 1.

5650

CALL PRINT
[021BH]

GOSUB to 021BH.
NOTE: 021BH will display the character at (HL) until a 03H is found.

5653

LD HL,NAMARO

LET Register Pair HL = 5686H to point to the message “—->“.

5656

CALL PRINT
[021BH]

GOSUB to 021BH.
NOTE: 021BH will display the character at (HL) until a 03H is found.

5659

LD HL,NAME2

LET Register Pair HL = 5676H to point to FILENAME 2.

565C

CALL PRINT
[021BH]

GOSUB to 021BH.
NOTE: 021BH will display the character at (HL) until a 03H is found.

565F

CALL S6CR
[5450H]

GOSUB to 5450H to display a carriage return via a JUMP to 0033H in the Model III ROM.

5662

POP HL

Put the value held at the top of the STACK into Restore Register Pair HL, and then remove the entry from the stack.

5663

POP DE

Put the value held at the top of the STACK into Restore Register Pair DE, and then remove the entry from the stack.

5664

POP BC

Put the value held at the top of the STACK into Restore Register Pair BC, and then remove the entry from the stack.

5665

RET

RETurn to the caller.

MESSAGE STORAGE AREA for the RENAME Command.

“NAME1”
5666

DEFM …

PRINT BUFFER FOR FILESPEC 1 of 16 characters.

“NAME2”
5676

DEFM …

PRINT BUFFER FOR FILESPEC 2 of 16 characters.

“NAMARO”
5686

DEFM …

—->.

568EH – “APPEND” Command.

“APPEND”
568E

CALL GETSYN
[623AH]

GOSUB to 623AH to isolate and validate the FILESPEC from the command line via an OVERLAY call to ROUTINE 4 of OVERLAY 1.

5691

JP NZ,ERR3
[5218H]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned because of an ERROR, JUMP to 5218H.

5694

LD DE,S6DCB2

LET Register Pair DE = 62B2H to point to FILESPEC 2’s FCB.

5697

CALL SYNTAX
[441CH]

GOSUB to 441CH.
NOTE: 441CH is the SYS00/SYS routine to CHECK THE SYNTAX OF A FILESPEC before for use. This RST 28H’s with a value of C1H so as to call ROUTINE 4 in OVERLAY 1.

569A

JP NZ,ERR3
[5218H]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned because of an ERROR, JUMP to 5218H.

569D

LD B,00H

LET Register B = 00H to signify a 256 Byte Full Sector LRL.

569F

LD HL,S6BUF2

LET Register Pair HL = 6400H for a memory buffer.

56A2

CALL OPEN
[4424H]

GOSUB to 4424H to open FILESPEC 2.
NOTE: 4424H is the SYS00/SYS routine to OPEN A DISK FILE for use. This RST 28H’s with a value of 92H so as to call ROUTINE 1 in OVERLAY 3.

56A5

JP NZ,ERR
[6132H]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned because of an ERROR, JUMP to 6132H.

56A8

CALL OPENIT
[6225H]

GOSUB to 6225H to open FILESPEC 1.

56AB

JP NZ,ERR
[6132H]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned because of an ERROR, JUMP to 6132H.

56AE

LD A,(S6DCB1 + LRL)

Fetch the value stored at memory location 6289H (i.e., the LRL for FILESPEC 1) and put it into Register A.

56B1

LD B,A

LET Register B = Register A (i.e., the LRL for FILESPEC 1).

56B2

LD A,(S6DCB2 + LRL)

Fetch the value stored at memory location 62BBH (i.e., the LRL for FILESPEC 2) and put it into Register A.

56B5

CP B

Compare the value held in Register A against the value held in Register B. Results: If Register A equals Register B (meaning that both files LRL’s are the same), the Z FLAG is set; otherwise the NZ FLAG is set.

56B6

JP NZ,ERR13
[522FH]

If the file LRL’s are different, then the the NZ FLAG (Not Zero) will be set so JUMP to 522FH.

56B9

LD DE,S6DCB2

LET Register Pair DE = 62B2H to point to the FCB for FILESPEC 2.

56BC

CALL POSEOF
[4448H]

GOSUB to 4448H.
NOTE: 4448H is the SYS00/SYS vector for ‘POSEOF’, which positions the disk drive to the last record of the open file.

56BF

JR Z,L6OP10
[56C6H]

If that CALL routine exited with no error, the Z FLAG (Zero) will be set, so in that case JUMP to 56C6H.

56C1

CP EEOF

Compare the value held in Register A against 1CH (i.e., an END OF FILE error). Results: If Register A equals 1CH, the Z FLAG is set; otherwise the NZ FLAG is set.

56C3

JP NZ,ERR
[6132H]

If the NZ FLAG (Not Zero) is set, then we do have an error, just not END OF FILE, so JUMP to 6132H.

“L6OP10”
56C6

LD DE,S6DCB1

LET Register Pair DE = 6280H to point to the FCB for FILESPEC 1.

56C9

CALL GET
[0013H]

Try to read a byte from FILESPEC 1 by GOSUBing to 0013H which is the Model III ROM routine to read a byte from an input device. Requires DE = starting address of DCB of device and on Exit Register A = byte received from device, Z set if device ready. Uses AF.

56CC

JR Z,CONT
[56DAH]

If the Z FLAG (Zero) is set, then that CALL returned a DEVICE READY, so JUMP to 56DAH.

56CE

LD B,A

LET Register B = Register A (i.e., the error code returned from the CALL GET).

56CF

AND 0FEH

MASK the value of Register A against 0FEH (1111 1110) to turn off bit 0.

56D1

CP EEOF

Compare the value held in Register A against 1CH (i.e., the END OF FILE error code). Results:

If Register A equals 1CH, the Z FLAG is set.
If A < 1CH, the CARRY FLAG will be set.
if A >= 1CH/ 28/, the NO CARRY FLAG will be set.

56D3

LD A,B

LET Register A = Register B (i.e., the error code returned from the CALL GET).

56D4

JP Z,CLOZE
[56EDH]

If the Z FLAG (Zero) is set, then while we have a problem we do not care because we are done appending, so JUMP to 56EDH to close the files and RETURN.

56D7

JP ERR
[6132H]

JUMP to 6132H to exit the APPEND routine with an error.

56DAH – Continuation of APPEND Command. This routine is jumped to from 56CC if we got a DEVICE READY regarding FILESPEC 1 after reading a byte.

“CONT”
56DA

LD B,A

LET Register B = Register A (i.e., the byte read from FILESPEC 1 via a ROM call to 0013H) in 56C9.

56DB

CALL BRKCHK
[028DH]

GOSUB to 028DH.
NOTE: 028DH is the Model III ROM routine to CHECK FOR BREAK. On exit, the NZ FLAG will be set if BREAK was detected.

56DE

JP NZ,CLOZE
[56EDH]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned a BREAK, so JUMP to 56EDH to close the files and RETURN.

56E1

LD A,B

LET Register A = Register B (i.e., the byte read from FILESPEC 1).

56E2

LD DE,S6DCB2

LET Register Pair DE = 62B2H to point to FILESPEC 2’s FCB.

56E5

CALL PUT
[001BH]

GOSUB to 001BH
NOTE: 001BH is the Model III ROM routine to write a byte to an output device. Requires Register A to contain the byte to output and Register Pair DE to be the starting address of DCB of device. On exit, Z set if device ready. Uses AF.

56E8

JP NZ,ERR
[6132H]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned because of an ERROR, JUMP to 6132H.

56EB

JR L6OP10
[56C6H]

LOOP back to 56C6H to continue processing bytes.

56EDH – Close FILESPEC 1 and FILESPEC 2 and RETurn.

“CLOZE”
56ED

LD DE,62B2H

LET Register Pair DE = 62B2H to point to FILESPEC 2’s FCB.

56F0

CALL CLOSE
[4428H]

GOSUB to 4428H to CLOSE the file for FILESPEC 2.

56F3

JP NZ,ERR
[6132H]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned because of an ERROR, JUMP to 6132H.

“CLOZE1”
56F6

LD DE,S6DCB1

LET Register Pair DE = 6280H to point to FILESPEC 1’s FCB.

“CLOZE2”
56F9

CALL CLOSE
[4428H]

GOSUB to 4428H to CLOSE the file for FILESPEC 1.

56FC

JP NZ,ERR
[6132H]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned because of an ERROR, JUMP to 6132H.

56FF

RET

RETurn to the caller.

5700H – “DUMP” Command.

The DUMP command storeas a program into a disk file. The command structure is:

DUMP file (START=aaaa,END=bbbb,TRA=cccc,RELO=dddd)

aaaa = The 4 hexadecimal digit start address of the memory block to dump.

bbbb = The 4 hexadecimal digit end address of the memory block to dump.

cccc = The 4 hexadecimal digit transfer address to use to execute the program once it has been loaded. If blank, TRSDOS RE-ENTRY is used.

dddd = The 4 hexadecimal digit start address for relocating or loading the program back into memory. If blank, no relocation is done

Note: All hexadecimal numbers which begin with a letter must start with a 0. No x’____’ notation is used.

“DUMP”
5700

LD BC,6000H

LET Register Pair BC = 6000H which will be the default START and END numbers.

5703

LD (START),BC

Store the value held in Register BC (i.e., 6000H) into the memory location 57B1H (which is the memory location for the START address).

5707

LD (END),BC

Store the value held in Register BC (i.e., 6000H) into the memory location 57BBH (which is the memory location for the END address).

570B

XOR A

Set Register A to ZERO and clear all Flags.

570C

LD (DCOUNT),A

Store the value held in Register A into the memory location 5845H (which is the memory location for the DUMP PARAMETER TABLE).

570F

LD BC,0000H

LET Register Pair BC = 0000H which will be the default RELO number.

5712

LD (RELO),BC

Store the value held in Register BC into the memory location 57B5H (which is the memory location for the RELO address).

5716

LD BC,402DH

LET Register Pair BC = 402DH which will be the default TRA number.

5719

LD (TRA),BC

Store the value held in Register BC into the memory location 5800H (which is the memory location for the TRA address which is ALSO in the middle of a LD HL,nnnnH OPCODE).

571D

CALL GETSYN
[623AH]

GOSUB to 623AH to isolate and validate the FILESPEC from the command line via an OVERLAY call to ROUTINE 4 of OVERLAY 1.

5720

JP NZ,ERR3
[5218H]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned because of an ERROR, JUMP to 5218H.

5723

LD DE,SWTCH7

LET Register Pair DE = 5825H to point to the DUMP PARAMETER TABLE.

5726

CALL SWITCH
[4454H]

GOSUB to 4454H.
NOTE: 4454H is the DOS PARAMETER STRING PARSE routine. It decodes DOS LIBRARY parameters.

5729

JP NZ,ERR2
[5214H]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned because of an ERROR, JUMP to 5214H.

“DUMP10”
572C

LD DE,NAMFIL

LET Register Pair DE = 5846H, which is an 8 BYTE storage area for the FILENAME.

572F

LD HL,S6DCB1

LET Register Pair HL = 6280H, which is where the filename is currently stored.

5732

LD B,08H

LET Register B = 08H to signify an 8 character DJNZ loop.

“L6OP70”
5734

LD A,(HL)

Fetch the value stored at memory location pointed to by Register Pair HL (i.e., the scratch location where the filename is current stored) and put it into Register A.

5735

CALL LEAL
[59CBH]

GOSUB to 59CBH to test the validity of the character of the filename stored in Register A.

5738

JR C,SPCFIL
[5741H]

If the C FLAG (Carry) is set then that routine returned a result that the character of the filename stored in Register A is INVALID. JUMP to 5741 to stop reading/processing characters from the scratch area and fill the rest of the filename with spaces.

“FILASC”
573A

LD (DE),A

Store the value held in Register A (i.e., the validated character of the filename) into the memory location pointed to by Register Pair DE (i.e., the 8 BYTE storage area for the FILENAME).

573B

INC HL

INCrement the value stored in Register Pair HL by 1 to point to the next character in the filename held in the scratch area.

573C

INC DE

INCrement the value stored in Register Pair DE by 1 to point to the next character in the 8 BYTE storage area for the FILENAME.

573D

DJNZ L6OP70
[5734H]

LOOP back to 5734H, reducing Register B each time, and continue to LOOP until Register B has been reduced to ZERO, in which case, continue with the next instruction.

573F

JR CONTH
[5747H]

JUMP to 5747H to continue the “DUMP” routine.

5741H – Part of the DUMP command. Jumped here if the character of the filename stored in Register A is INVALID.

“SPCFIL”
5741

LD A,20H

LET Register A = 20H (ASCII: SPACE).

“L6OP75”
5743

LD (DE),A

Store the value held in Register A (i.e., a SPACE) into the memory location pointed to by Register Pair DE (i.e., the 8 BYTE storage area for the FILENAME).

5744

INC DE

INCrement the value stored in Register Pair DE by 1 to point to the next byte in the 8 BYTE storage area for the FILENAME.

5745

DJNZ L6OP75
[5743H]

LOOP back to 5743H, reducing Register B each time, and continue to LOOP until Register B has been reduced to ZERO, in which case, continue with the next instruction.

“CONTH”
5747

LD DE,S6DCB1

LET Register Pair DE = 6280H, which is where the filename is currently stored.

574A

LD HL,CMD

LET Register Pair HL = 5822H, which points to a /CMD message.

574D

CALL PUTEXT
[444BH]

GOSUB to 444BH to add the extension pointed to by Register Pair HL to the end of the filename pointed to by Register Pair DE.

5750

LD B,00H

LET Register B = 00H to set up for creating a file with an LRL of 256.

5752

LD HL,S6BUF1

LET Register Pair HL = 6300H to use as a buffer for the 4420H CALL.

5755

CALL INIT
[4420H]

GOSUB to 4420H.
NOTE: 4420H is the SYS00/SYS routine to INITIALIZE A DISK (i.e., CREATE or OPEN). This RST 28H’s with a value of A2H so as to call ROUTINE 2 in OVERLAY 2. Register HL needs to point to a RAM BUFFER for the DCB’s.

5758

JP NZ,ERR
[6132H]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned because of an ERROR, JUMP to 6132H.

575B

LD A,05H

LET Register A = 05H, which is a COMMENT BLOCK designator.

575D

CALL PUTIT
[581CH]

GOSUB to 581CH to write the contents of Register A (i.e., a COMMENT BLOCK designator) to the file.

5760

JP NZ,ERR
[6132H]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned because of an ERROR, JUMP to 6132H.

5763

LD A,10H

LET Register A = 10H (Decimal: 16) to set up the next CALL for a write of 16 bytes.

5765

CALL PUTIT
[581CH]

GOSUB to 581CH to write the contents of Register A (i.e., 10H) to the file.

5768

LD B,08H

LET Register B = 08H, to set up for a DJNZ loop of 8 characters, which is the length of the FILESPEC.

576A

LD HL,NAMFIL

LET Register Pair HL = 5846H, which is an 8 BYTE storage area for the FILENAME.

“L6OP71”
576D

LD A,(HL)

Fetch the value stored at memory location pointed to by Register Pair HL (i.e., a current byte from the FILESPEC) and put it into Register A.

576E

INC HL

INCrement the value stored in Register Pair HL by 1 to point to the next byte of the FILESPEC.

576F

CALL PUTIT
[581CH]

GOSUB to 581CH to write the contents of Register A (i.e., a byte of the filename) to the file.

5772

DJNZ L6OP71
[576DH]

LOOP back to 576DH, reducing Register B each time, and continue to LOOP until Register B has been reduced to ZERO, in which case, continue with the next instruction.

5774

PUSH BC

Save Register Pair BC to the top of the stack.

5775

PUSH DE

Save Register Pair DE to the top of the stack.

5776

PUSH IX

Save Register Pair IX to the top of the stack.

5778

LD C,2FH

LET Register C = 2FH (ASCII: /) in preparation for writing the DATE.

577A

CALL MSGPR0
[61F0H]

GOSUB to 61F0H to generate the date and place it into the file.

577D

POP IX

Put the value held at the top of the STACK into Restore Register Pair IX, and then remove the entry from the stack.

577F

POP DE

Put the value held at the top of the STACK into Restore Register Pair DE, and then remove the entry from the stack.

5780

POP BC

Put the value held at the top of the STACK into Restore Register Pair BC, and then remove the entry from the stack.

5781

LD B,08H

LET Register B = 08H, to set up for a DJNZ loop of 8 characters, which is the length of the DATE.

“L6OP91”
5783

LD A,(HL)

Fetch the value stored at memory location pointed to by Register Pair HL and put it into Register A.

5784

INC HL

INCrement the value stored in Register Pair HL by 1.

5785

CALL PUTIT
[581CH]

GOSUB to 581CH to write the contents of Register A (i.e., a byte of the DATE) to the file.

5788

DJNZ L6OP91
[5783H]

LOOP back to 5783H, reducing Register B each time, and continue to LOOP until Register B has been reduced to ZERO, in which case, continue with the next instruction.

578A

LD HL,(END)

Fetch the value stored at memory location 57BBH (i.e., the END address) and put it into Register HL.

578D

LD BC,(START)

Fetch the value stored at memory location 57B1H (i.e., the START address) and put it into Register BC.

5791

OR A

Set FLAGS based on the contents of Register A.

5792

SBC HL,BC

Subtracts the value stored in Register Pair BC (i.e., the START address) and the carry flag from the value stored in Register Pair HL (i.e., the END address).

5794

JP C,ERR5
[5220H]

If the C FLAG (Carry) is set, then the END address in HL was > the START address in DE, which is a problem, so JUMP to 5220H.

5797

LD HL,5FFFH

LET Register Pair HL = 5FFFH, which is 1 byte below the lowest permitted START address.

579A

SBC HL,BC

Subtracts the value stored in Register Pair BC (i.e., the START address) and the carry flag from the value stored in Register Pair HL (i.e., 5FFFH, which is the lowest permitted START address).

579C

JP NC,ERR6
[5225H]

If the NC FLAG (No Carry) is set, then the START address is too low, so JUMP to 5225H.

579F

LD HL,(RELO)

Fetch the value stored at memory location 57B5H (i.e., the RELO address) and put it into Register HL.

57A3
57A2

LD A,H
OR L

57A4

JR NZ,RELO1
[57B0H]

If the NZ FLAG (Not Zero) is set, then we have a RELO parameter to deal with, so JUMP to 57B0H.

57A6

LD HL,(START)

Fetch the value stored at memory location 57B1H (i.e., the START address) and put it into Register HL.

57A9

LD (RELO),HL

Store the value held in Register HL (i.e., the START address) into the memory location 57B5H (i.e., the RELO address).

57AC

LD IX,DCOUNT

LET Register Pair IX = 5845H so as to point to the FILENAME.

“RELO1”
57B0

LD HL,START

LET Register Pair HL = the value put into 57B1H, which is the START address.

57B3

LD IY,RELO

LET Register Pair IY = the value put into 57B5H, which is the RELO address.

“L6OP73”
57B7

PUSH HL

Save Register Pair HL (i.e., the START address) to the top of the stack.

57B8

LD B,H

LET Register B = Register H (i.e., MSB of the the START address).

57B9

LD C,L

LET Register C = Register L (i.e., LSB of the the START address).

57BA

LD HL,END

LET Register Pair HL = the value put into 57BBH, which is the END address.

57BD

INC HL

INCrement the value stored in Register Pair HL (i.e., the END address) by 1.

57BE

OR A

Set FLAGS based on the contents of Register A, which clears the CARRY FLAG.

57BF

SBC HL,BC

Subtracts the value stored in Register Pair BC (i.e., the START address) and the carry flag from the value stored in Register Pair HL (i.e., the END address + 1). With this, HL will now contain the number of bytes to save.

57C1

JR Z,DOEND
[57F4H]

If the Z FLAG (Zero) is set, then there are no bytes to save, so JUMP to 57F4H.

57C3

LD B,0FEH

LET Register B = 0FEH for a loop of 254 bytes to write each time.

57C5

LD A,H

LET Register A = Register H (i.e., the MSB of the number of bytes to save).

57C6

OR A

Since a LD command does not set any FLAGS, Set FLAGS based on the contents of Register A.

57C7

JR NZ,DUMP1
[57CFH]

If the NZ FLAG (Not Zero) is set, then there is more than just one page (meaning the number of bytes was more than what the LSB could hold) so JUMP to 57CFH.

57C9

LD A,L

LET Register A = Register L (i.e., the LSB of the number of bytes to save).

57CA

CP 0FFH

Compare the value held in Register A against 0FFH (Decimal: 255). Results:

If Register A equals 255, the Z FLAG is set.
If A < 255, the CARRY FLAG will be set.
if A >= 255, the NO CARRY FLAG will be set.

57CC

JR NC,DUMP1
[57CFH]

If the NC FLAG (No Carry) is set, then there are 255 or more bytes, which is still too many since we need to write 254, so JUMP to 57CFH.

57CE

LD B,L

LET Register B = Register L (i.e., the LSB of the number of bytes to save).

“DUMP1”
57CF

POP HL

Put the value held at the top of the STACK (i.e., the START address) into Restore Register Pair HL, and then remove the entry from the stack.

57D0

LD A,01H

LET Register A = 01H, which is code for a DATA BLOCK.

57D2

CALL PUTIT
[581CH]

GOSUB to 581CH to write the contents of Register A (i.e., a DATA BLOCK designator) to the file.

57D5

LD A,B

LET Register A = Register B (i.e., the LSB of the number of bytes to save).

57D6

ADD A,02H

LET Register A = Register A + 02H (i.e., the the number of bytes to save + 2).

57D8

CALL PUTIT
[581CH]

GOSUB to 581CH to write the contents of Register A (i.e., the number of bytes about to be written) to the file.

57DB

PUSH IY

Save Register Pair IY (i.e., the RELO address) to the top of the stack.

57DD

EX (SP),HL

EXchange the value stored in Register Pair HL (i.e., the total number of bytes to save) with the value stored at the top of the STACK (i.e., the RELO address).

57DE

LD A,L

LET Register A = Register L (i.e., the LSB of the RELO address), which means we are writing out the RELO address instead of the TRANSFER address.

57DF

CALL PUTIT
[581CH]

GOSUB to 581CH to write the contents of Register A (i.e., the MSB of the RELO address) to the file.

57E2

LD A,H

LET Register A = Register H (i.e., the MSB of the RELO address), which means we are writing out the RELO address instead of the TRANSFER address.

57E3

EX (SP),HL

EXchange the value stored in Register Pair HL (i.e., the RELO address) with the value stored at the top of the STACK (i.e., the total number of bytes to save).

57E4

POP IY

Put the value held at the top of the STACK (i.e., the RELO address) into Restore Register Pair IY, and then remove the entry from the stack.

57E6

CALL PUTIT
[581CH]

GOSUB to 581CH to write the contents of Register A (i.e., the MSB of the RELO address) to the file.

“L6OP72”
57E9

LD A,(HL)

Fetch the value stored at memory location pointed to by Register Pair HL (i.e., a data byte) and put it into Register A.

57EA

INC HL

INCrement the value stored in Register Pair HL (i.e., a data byte) by 1.

57EB

INC IY

INCrement the value stored in Register Pair IY (i.e., the RELO address) by 1.

57ED

CALL PUTIT
[581CH]

GOSUB to 581CH to write the contents of Register A (i.e., a data byte) to the file.

57F0

DJNZ L6OP72
[57E9H]

LOOP back to 57E9H (which is looping L), reducing Register B each time, and continue to LOOP until Register B has been reduced to ZERO, in which case, continue with the next instruction.

57F2

JR L6OP73
[57B7H]

BIG LOOP back to 57B7H until all of H is also exhausted.

57F4H – Part of the “DUMP” COMMAND. Jumped here when there are no more bytes to save.

“DOEND”
57F4

POP HL

Clear the STACK.

In a /CMD file, the TRANSFER address format is 02 nn xx yy, where nn is the length of the block, xx=the LSB, and yy=the MSB.

57F5

LD A,02H

LET Register A = 02H, which is code for the EXECUTION ADDRESS.

57F7

CALL PUTIT
[581CH]

GOSUB to 581CH to write the contents of Register A (i.e., an 02H) to the file.

57FA

LD A,02H

LET Register A = 02H, which is code for the EXECUTION ADDRESS block length (i.e., 2 bytes – a LSB and a MSB).

57FC

CALL PUTIT
[581CH]

GOSUB to 581CH to write the contents of Register A (i.e., an 02H) to the file.

57FF

LD HL,TRA

LET Register Pair HL = the value stored in 5800H-5801H, which was placed here by other code. It is where the TRANSFER ADDRESS has been stored.

5802

LD A,L

LET Register A = Register L (i.e., the LSB of the TRANSFER ADDRESS).

5803

CALL PUTIT
[581CH]

GOSUB to 581CH to write the contents of Register A (i.e., the LSB of the TRANSFER ADDRESS) to the file.

5806

LD A,H

LET Register A = Register H (i.e., the MSB of the TRANSFER ADDRESS).

5807

CALL PUTIT
[581CH]

GOSUB to 581CH to write the contents of Register A (i.e., the MSB of the TRANSFER ADDRESS) to the file.

580A

LD A,(DCOUNT)

Fetch the value stored at memory location 5845H (i.e., the number of bytes left in the sector) and put it into Register A so as to check to see if the last sector is full or not.

580D

OR A

Since a LD command does not set any FLAGS, Set FLAGS based on the contents of Register A.

580E

JP Z,CLOZE2
[56F9H]

If the Z FLAG (Zero) is set, then the last sector is full, so JUMP to 56F9H to close the file.

5811

LD B,A

LET Register B = Register A (i.e., the number of bytes left in the sector) to prepare for DJNZ loop.

“TRA1”
5812

LD A,0E5H

LET Register A = 0E5H, which will be the value to fill the rest of the sector with.

5814

CALL PUT
[001BH]

GOSUB to 001BH
NOTE: 001BH is the Model III ROM routine to output a byte (held in Register A) to a device. Register Pair DE has the DCB of the device to be output to. Z is set if the device is ready.

5817

DJNZ TRA1
[5812H]

LOOP back to 5812H, reducing Register B each time, and continue to LOOP until Register B has been reduced to ZERO, in which case, continue with the next instruction.

5819

JP CLOZE2
[56F9H]

JUMP to 56F9H to close the file and exit.

581CH – Part of the “DUMP” command. This routine is called each time a byte needs to be written, as it also includes that that byte in the running byte count.

“PUTIT”
581C

INC (IX+00H)

IX+00H points to the byte-in-sector counter, so this bumps that by 1.

581F

JP PUT
[001BH]

to 001BH
NOTE: 001BH is the Model III ROM routine to output a byte (held in Register A) to a device. Register Pair DE has the DCB of the device to be output to. Z is set if the device is ready.

5822H – MESSAGE and RAM STORAGE AREA for the DUMP COMMAND.

“CMD”
5822

DEFM …

“CMD“.

“SWITCH7”
5825

DEFM …

“START “.

582D

DEFM …

“END “.

5835

DEFM …

“TRA “.

583D

DEFM …

“RELO “.

“DCOUNT”
5845

00H

END OF TABLE DESIGNATOR.

“NAMFIL”
5846

DEFB 08H

8-Byte Storage Location for the Filename.

584FH – “LOAD” Command.

The LOAD command loads a memory image file from disk. After the load, DOS returns to TRSDOS READY.

“LOAD”
584F

CALL GETSYN
[5FBFH]

GOSUB to 5FBFH to get the filespec.

5852

JP NZ,ERR3
[5218H]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned because of an ERROR, JUMP to 5218H.

5855

LD IY,SYS1IN

LET Register Pair IY = 402DH which will be the RETURN address for RETURN TO DOS when done.

5859

PUSH IY

Save Register Pair IY (i.e., the return address) to the top of the stack.

585B

JP LDPGM
[4430H]

JUMP to 4430H.
NOTE: 4430H is DOS PROGRAM LOADER routine and does the same as the DOS LIBRARY command of LOAD. Requires Register Pair DE to contain the applicable FCB. All Registers are modified.

585EH – “ATTRIB” Command.

ATTRIB lets you change the passwords to an existing file or makes the file invisible or non-invisible. Passwords are initially assigned when the file is created. At that time, the update and access words are set to the same value (either the password you specified or a blank password).

ATTRIB file (visibility,ACC = name,UPD = name,PROT = level)
file = file specification.
visibility must be I or N.
ACC=password. If omitted, the access password is unchanged. set to “ACC=“, password is set to blanks.
UPD=password. If omitted, the update password is unchanged. set to “UPD=“, password is set to blanks.
PROT=Protection level. If omitted, it remains unchanged.

FUL = full access, no protection.
KILL = Kill, rename, read, execute, and write (gives total access, i.e., the least-protected).
NAME = Rename, read, execute, and write.
WRITE = Read, execute, and write.
READ = Read and execute.
EXEC = Execute only.

“ATTRIB”
585E

CALL GETSYN
[623AH]

GOSUB to 623AH to isolate and validate the FILESPEC from the command line via an OVERLAY call to ROUTINE 4 of OVERLAY 1.

5861

JP NZ,ERR3
[5218H]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned because of an ERROR, JUMP to 5218H.

5864

PUSH HL

Save Register Pair HL (i.e., the parameter address) to the top of the stack.

5865

LD B,00H

LET Register B = 00H to set a LRL = 0.

5867

LD HL,S6BUF2

LET Register Pair HL = 6400H as a buffer.

586A

CALL OPEN
[4424H]

GOSUB to 4424H.
NOTE: 4424H is the SYS00/SYS routine to OPEN A DISK FILE for use. This RST 28H’s with a value of 92H so as to call ROUTINE 1 in OVERLAY 3.

586D

POP HL

Put the value held at the top of the STACK (i.e., the parameter address) into Register Pair HL, and then remove the entry from the stack.

586E

JP NZ,ERR
[6132H]

If the NZ FLAG (Not Zero) is set, JUMP to 6132H.

5871

LD A,(S6DCB1 + PROT)

Fetch the value stored at memory location 6281H (i.e., the FILE ACCESS LEVEL) and put it into Register A.

5874

AND 07H

MASK the value of Register A against 07H (0000 0111) to isolate the protection level bits. This has the effect of turning off bits 7, 6, 5, 4, 3, leaving only bits 2, 1, 0 active.

5876

LD A,EFAD

LET Register A = 19H to set up for a FILE ACCESS DENIED.

5878

JP NZ,ERR
[6132H]

If the NZ FLAG (Not Zero) is set, that is the error we got, so exit via a JUMP to 6132H.

587B

XOR A

Set Register A to ZERO and clear all Flags.

587C

LD (STAT),A

Store the value held in Register A (i.e., a 0) into the memory location 597BH (i.e., the file protection status).

587F

LD (ISTAT),A

Store the value held in Register A (i.e., a 0) into the memory location 5983H (i.e., invisible status).

5882

DEC A

DECrement the value stored in Register A by 1 (i.e., to FFH).

5883

LD (ISTAT1),A

Store the value held in Register A (i.e., FFH) into the memory location 5985H (i.e., non-invisible status).

“L6OP40”
5886

LD A,(HL)

Fetch the value stored at memory location pointed to by Register Pair HL (i.e., the parameter character) and put it into Register A.

5887

CP 28H

Compare the value held in Register A against 28H (ASCII: (). Results: If Register A equals (, the Z FLAG is set; otherwise the NZ FLAG is set.

5889

JR Z,NEXTA
[5893H]

If the Z FLAG (Zero) is set then we got the (, so JUMP to 5893H.

588B

CP 20H

Compare the value held in Register A against 20H SPACE). Results: If Register A equals SPACE, the Z FLAG is set; otherwise the NZ FLAG is set.

588D

JP NZ,ERR3
[5218H]

If the NZ FLAG (Not Zero) is set, then we didn’t get the SPACE that we were expecting, so JUMP to 5218H.

5890

INC HL

INCrement the value stored in Register Pair HL by 1 to point to the next character.

5891

JR L6OP40
[5886H]

LOOP back to 5886H to look for a (.

5893H – Continuation of the “ATTRIB” Command. Jumped here if a “(” was Found.

“NEXTA”
5893

INC HL

INCrement the value stored in Register Pair HL by 1 to point to the next character.

5894

LD A,(HL)

Fetch the value stored at memory location pointed to by Register Pair HL (i.e., the next character) and put it into Register A.

5895

CP 49H

Compare the value held in Register A against 49H (ASCII: I). Results: If Register A equals I, the Z FLAG is set; otherwise the NZ FLAG is set.

5897

JR Z,INVISB
[58FAH]

If the character was a I, then the Z FLAG (Zero) will be set. JUMP to 58FAH for the INVISIBLE ATTRIBUTE.

5899

CP 4EH

Compare the value held in Register A against 4EH (ASCII: N). Results: If Register A equals N, the Z FLAG is set; otherwise the NZ FLAG is set.

589B

JR Z,NONINV
[590AH]

If the character was a N, then the Z FLAG (Zero) will be set. JUMP to 590AH for the NOT INVISIBLE ATTRIBUTE.

589D

CP 41H

Compare the value held in Register A against 41H (ASCII: A). Results: If Register A equals A, the Z FLAG is set; otherwise the NZ FLAG is set.

589F

JP Z,ACCESS
[591AH]

If the character was a A, then the Z FLAG (Zero) will be set. JUMP to 591AH to change the ACCESS PASSWORD.

58A2

CP 55H

Compare the value held in Register A against 55H (ASCII: U). Results: If Register A equals U, the Z FLAG is set; otherwise the NZ FLAG is set.

58A4

JP Z,UPDATE
[592FH]

If the character was a U, then the Z FLAG (Zero) will be set. JUMP to 592FH to change the UPDATE PASSWORD.

58A7

CP 50H

Compare the value held in Register A against 50H (ASCII: P). Results: If Register A equals P, the Z FLAG is set; otherwise the NZ FLAG is set.

58A9

JP NZ,ERR3
[5218H]

If the character was a P, then the Z FLAG (Zero) will be set. JUMP to 5218H to change the PROTECTIONAL LEVEL.

58AC

CALL GETEND
[5944H]

GOSUB to 5944H to get the next parameter.

58AF

JP Z,ERR3
[5218H]

If the Z FLAG (Zero) is set then there was an error, so JUMP to 5218H.

58B2

PUSH HL

Save Register Pair HL (i.e., the current position on the parameter line) to the top of the stack.

58B3

LD B,PNOACC

LET Register B = 07H, for a loop of 7 entries.

58B5

LD DE,(PWORD)

Fetch the value stored at memory location 5139H (i.e., the parameter) and put it into Register DE.

58B9

LD HL,INDEX

LET Register Pair HL = 59AFH to point to the LEVEL TABLE.

“L6OP38”
58BC

LD A,(HL)

Fetch the value stored at memory location pointed to by Register Pair HL (i.e., a character from the LEVEL TABLE) and put it into Register A.

58BD

INC HL

INCrement the value stored in Register Pair HL by 1 to point to the next character in the LEVEL TABLE.

58BE

CP E

Compare the value held in Register A against the value held in Register E. Results: If Register A equals Register E/, the Z FLAG is set; otherwise the NZ FLAG is set.

58BF

CALL Z,CMP2
[58C8H]

If the Z FLAG (Zero) is set, then Register A = Register E, so GOSUB to 58C8H to check the rest of the characters.

58C2

INC HL

INCrement the value stored in Register Pair HL by 1 to point to the next character in the LEVEL TABLE.

58C3

DJNZ L6OP38
[58BCH]

LOOP back to 58BCH to check the rest of the table, reducing Register B each time, and continue to LOOP until Register B has been reduced to ZERO, in which case, continue with the next instruction.

58C5

JP ERR3
[5218H]

JUMP to 5218H to exit the routine as this means there was no match found.

58C8H – Continuation of the “ATTRIB” Command. Jumped here during the LEVEL TABLE search when the first character of the desired level matches the first character in the level table; to check the rest for matches

“CMP2”
58C8

LD A,(HL)

Fetch the value stored at memory location pointed to by Register Pair HL (i.e., a character from the ACCESSS LEVEL TABLE) and put it into Register A.

58C9

CP D

Compare the value held in Register A against the value held in Register D. Results:

If Register A equals Register D, the Z FLAG is set.
If A < D, the CARRY FLAG will be set.
if A >= D/ 22959/, the NO CARRY FLAG will be set.

58CA

RET NZ

If the NZ FLAG (Not Zero) is set then the SECOND character did NOT match, so RETurn to the caller.

58CB

POP AF

Clear the top value held on the STACK (which was the RETurn value).

58CC

LD A,B

LET Register A = Register B (i.e., the access level).

58CD

DEC A

DECrement the value stored in Register A by 1.

58CE

CP PREAD

Compare the value held in Register A against 05H (which STILL could be either REad or REname). Results: If Register A 05H the Z FLAG is set; otherwise the NZ FLAG is set.

58D0

JR NZ,NOTRE
[58DDH]

If the NZ FLAG (Not Zero) is set then the second character didn’t match, so JUMP to 58DDH.

58D2

LD A,(PWORD + 2)

Fetch the value stored at memory location 513BH (i.e., the THIRD character) and put it into Register A.

58D5

CP 4EH

Compare the value held in Register A against 4EH (ASCII: N). Results:

If Register A equals N, the Z FLAG is set.
If A < N, the CARRY FLAG will be set.
if A >= N, the NO CARRY FLAG will be set.

58D7

LD A,PREAD

LET Register A = 05H to restore the level.

58D9

JR NZ,NOTRE
[58DDH]

If the NZ FLAG (Not Zero) is set then the third character didn’t match as an N, so JUMP to 58DDH.

58DB

LD A,PNAME

LET Register A = 02H (i.e., “NAME”).

“NOTRE”
58DD

LD (STAT1),A

Store the value held in Register A (i.e., the access level of 2) into the memory location 5981H (i.e., the access level).

58E0

POP HL

Put the value held at the top of the STACK (i.e., the current position on the parameter line) into Restore Register Pair HL, and then remove the entry from the stack.

58E1

LD B,01H

LET Register B = 01H for a protection level test.

“END2”
58E3

LD A,(STAT)

Fetch the value stored at memory location 597BH (i.e., the file UPDATE protection status) and put it into Register A.

58E6

OR B

OR Register B against Register A to turn on bit zero. The results are stored in Register A.

58E7

LD (STAT),A

Store the value held in Register A into the memory location 597BH (i.e., the file UPDATE protection status).

“END3”
58EA

LD A,(HL)

Fetch the value stored at memory location pointed to by Register Pair HL (i..e, the next character) and put it into Register A.

58EB

CP 29H

Compare the value held in Register A against 29H (ASCII: )). Results: If Register A equals ), the Z FLAG is set; otherwise the NZ FLAG is set.

58ED

JR Z,DONEA
[596DH]

If the next character is a ), then the Z FLAG (Zero) will be set. JUMP to 596DH.

58EF

CP 2CH

Compare the value held in Register A against 2CH (ASCII: ,). Results: If Register A equals ,, the Z FLAG is set; otherwise the NZ FLAG is set.

58F1

JR Z,NEXTA
[5893H]

If the next character is a ), then the Z FLAG (Zero) will be set. JUMP to 5893H.

58F3

CP 20H

Compare the value held in Register A against 20H (ASCII: SPACE). Results:

If Register A equals SPACE, the Z FLAG is set.
If A < 20H, the CARRY FLAG will be set.
if A >= 20H/ 32/(ASCII: SPACE), the NO CARRY FLAG will be set.

58F5

JR C,DONEA
[596DH]

If the next character is < SPACE, then the C FLAG (Zero) will be set. JUMP to 596DH.

58F7

JP ERR3
[5218H]

If we are here then we didn’t get the character we expected, so we are going to exit with an error. JUMP to 5218H.

58FAH – Continuation of the “ATTRIB” Command. Jumped here if a “I” was found after a “(” was found.

“INVISB”
58FA

CALL GETEND
[5944H]

GOSUB to 5944H to position to the next parameter.

58FD

JP NZ,ERR3
[5218H]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned because of an ERROR, JUMP to 5218H.

5900

LD A,(ISTAT)

Fetch the value stored at memory location 5983H (i.e., invisible status) and put it into Register A.

5903

OR 08H

OR Register A against 08H (0000 1000). This has the effect of turning on bit 3 to set the invisible status bit.

5905

LD (ISTAT),A

Store the value held in Register A into the memory location 5983H (i.e., invisible status).

5908

JR END3
[58EAH]

JUMP back inside the loop at 58EAH.

590AH – Continuation of the “ATTRIB” Command. Jumped here if a “N” was found after a “(” was found.

“NONINV”
590A

CALL GETEND
[5944H]

GOSUB to 5944H to position to the next parameter.

590D

JP NZ,ERR3
[5218H]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned because of an ERROR, JUMP to 5218H.

5910

LD A,(ISTAT1)

Fetch the value stored at memory location 5985H (i.e., non-invisible status) and put it into Register A.

5913

AND 0F7H

MASK the value of Register A against 0F7H (1111 0111). This has the effect of turning off bit 3, leaving all other bits active.

5915

LD (ISTAT1),A

Store the value held in Register A into the memory location 5985H (i.e., non-invisible status).

5918

JR END3
[58EAH]

JUMP back inside the loop at 58EAH.

591AH – Continuation of the “ATTRIB” Command. Jumped here if a “A” was found after a “(” was found.

“ACCESS”
591A

CALL GETEND
[5944H]

GOSUB to 5944H to position to the next parameter.

591D

JP Z,ERR2
[5214H]

If the Z FLAG (Zero) is set then no password was provided, so JUMP to 5214H.

5920

PUSH HL

Save Register Pair HL (i.e., the character in the command line) to the top of the stack.

5921

LD DE,PWORD

LET Register Pair DE = 5139H which is the PARAMETER STORAGE TABLE.

5924

CALL SETTDC
[5107H]

GOSUB to 5107H to encode the access password.

5927

LD (ACCTDC),HL

Store the value held in Register HL (i.e., encoded the access password) into the memory location 514EH.
NOTE: 514EH is the storage location for the ACCESS PASSWORD.

592A

POP HL

Put the value held at the top of the STACK (i.e., the character in the command line) into Restore Register Pair HL, and then remove the entry from the stack.

592B

LD B,02H

LET Register B = 02H to signify that the ACCESS PASSWORD is now active.

592D

JR END2
[58E3H]

JUMP back inside the loop at 58E3H.

592FH – Continuation of the “ATTRIB” Command. Jumped here if a “U” was found after a “(” was found.

“UPDATE”
592F

CALL GETEND
[5944H]

GOSUB to 5944H to position to the next parameter.

5932

JP Z,ERR2
[5214H]

If the Z FLAG (Zero) is set then no password was provided, so JUMP to 5214H.

5935

PUSH HL

Save Register Pair HL (i.e., the character in the command line) to the top of the stack.

5936

LD DE,PWORD

LET Register Pair DE = 5139H which is the PARAMETER STORAGE TABLE.

5939

CALL SETTDC
[5107H]

GOSUB to 5107H to encode the UPDATE password.

593C

LD (UPDTDC),HL

Store the value held in Register HL (i.e., encoded the ACCESS password) into the memory location 514CH.
NOTE: 514CH is the storage location for the UPDATE PASSWORD.

593F

POP HL

Put the value held at the top of the STACK (i.e., the character in the command line) into Restore Register Pair HL, and then remove the entry from the stack.

5940

LD B,04H

LET Register B = 04H to signify that the UPDATE PASSWORD is now active.

5942

JR END2
[58E3H]

JUMP back inside the loop at 58E3H.

5944H – Continuation of the “ATTRIB” Command. Jumped here to position to the next parameter on the command line.

“GETEND”
5944

INC HL

INCrement the value stored in Register Pair HL (i.e., the character in the command line) by 1.

5945

LD A,(HL)

Fetch the value stored at memory location pointed to by Register Pair HL (i.e., the character in the command line) and put it into Register A.

5946

CP 20H

Compare the value held in Register A against 20H (ASCII: SPACE). Results:

If Register A equals SPACE, the Z FLAG is set.
If A < SPACE, the CARRY FLAG will be set.
if A >= SPACE, the NO CARRY FLAG will be set.

5948

JR NC,GETEN1
[594CH]

If the character in the command line >= SPACE the NC FLAG (No Carry) is set. JUMP to 594CH.

594A

XOR A

Set Register A to ZERO and clear all Flags.

594B

RET

RETurn to the caller.

594CH – Continuation of the “ATTRIB” Command. Jumped here from the “position to next parameter” subroutine if a control character was detected.

“GETEN1”
594C

CP 29H

Compare the value held in Register A against 29H (ASCII: )). Results:

If Register A equals ), the Z FLAG is set.
If A < ), the CARRY FLAG will be set.
if A >= ), the NO CARRY FLAG will be set.

594E

RET Z

If we have a ) then we are done and the Z FLAG (Zero) is set. RETurn to the caller.

594F

CP 2CH

Compare the value held in Register A against 2CH (ASCII: ,). If Register A equals ,, the Z FLAG is set; otherwise the NZ FLAG is set.

5951

RET Z

If we have a , then we are done and the Z FLAG (Zero) is set. RETurn to the caller.

5952

CP 3DH

Compare the value held in Register A against 3DH (ASCII: =). If Register A equals =, the Z FLAG is set; otherwise the NZ FLAG is set.

5954

JR NZ,GETEND
[5944H]

If we did NOT get an =, the NZ FLAG is set. JUMP to 5944H to look at the next character.

5956

INC HL

INCrement the value stored in Register Pair HL (i.e., the character in the command line) by 1.

5957

LD DE,PWORD

LET Register Pair DE = 5139H which is the PARAMETER STORAGE TABLE.

595A

LD B,08H

LET Register B = 08H for a DJNZ loop of 8 characters.

595C

PUSH DE

Save Register Pair DE (i.e., the 9th character in the PARAMETER STORAGE TABLE) to the top of the stack.

595D

PUSH BC

Save Register Pair BC.

595E

LD A,20H

LET Register A = 20H (ASCII: SPACE).

“L6OP39”
5960

LD (DE),A

Store the value held in Register A (i.e., a SPACE) into the memory location pointed to by Register Pair DE (i.e., the pointer to the current byte of the PARAMETER STORAGE TABLE).

5961

INC DE

INCrement the value stored in Register Pair DE (i.e., the pointer to the current byte of the PARAMETER STORAGE TABLE) by 1.

5962

DJNZ L6OP39
[5960H]

LOOP back to 5960H, reducing Register B each time, and continue to LOOP until Register B has been reduced to ZERO, in which case, continue with the next instruction.

5964

POP BC

Put the value held at the top of the STACK into Restore Register Pair BC, and then remove the entry from the stack.

5965

POP DE

Put the value held at the top of the STACK (i.e., the 9th character in the PARAMETER STORAGE TABLE) into Restore Register Pair DE, and then remove the entry from the stack.

5966

CALL GETFLD
[50CDH]

GOSUB to 50CDH to get the parameter.

5969

DEC HL

DECrement the value stored in Register Pair HL (i.e., the character in the command line) by 1.

596A

OR 01H

OR Register A against 01H. This has the effect of turning on bit 0 to set the status.

596C

RET

RETurn to the caller.

596DH – Continuation of the “ATTRIB” Command. This will mask the values and set the passwords and put them in the RAM STORAGE LOCATION for the DIRECTORY ENTRY.

“DONEA”
596D

LD BC,(S6DCB1 + DRVNUM)

Fetch the value stored at memory location 6286H (i.e., drive number and file number) and put it into Register BC.

5971

CALL RDDIR
[4A67H]

GOSUB to 4A67H.
NOTE: 4A67H is the SYS00/SYS routine to read the directory entry into RAM (Buffer at 4300H).

5974

JP NZ,ERR
[6132H]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned because of an ERROR, JUMP to 6132H.

5977

LD A,(HL)

Fetch the value stored at memory location pointed to by Register Pair HL (i.e., the file type byte) and put it into Register A.

5978

AND 0F8H

MASK the value of Register A against 0F8H (1111 1000). This has the effect of turning off bits 2, 1, and 0; removing the access protection code.

597A

LD D,STAT

LET Register D = the contents of memory location 597BH, as set elsewhere. This will be the protection code.

597C

BIT 0,D

Test Bit Number 0 of Register D. Z FLAG will be set if that bit is 0, and NZ FLAG will be set if that bit is 1.

597E

JR Z,SKIP
[5982H]

If the Z FLAG (Zero) is set then there was no need to protect the file. JUMP to 5982H.

5980

OR STAT1

OR Register A against the contents of memory position 5981H, as set elsewhere. This will mask in the access level.

“SKIP”
5982

OR ISTAT

OR Register A against the contents of memory position 5983H, as set elsewhere. This will start a mask for invisibility.

5984

AND ISTAT1

AND Register A against the contents of memory position 5985H, as set elsewhere. This will finish a mask for invisibility.

5986

LD (HL),A

Store the value held in Register A (i.e., the masked file type byte) into the memory location pointed to by Register Pair HL.

5988
5987
598A

LD A,L
ADD A,DUPD
LD L,A

LET Register L = Register L + 10H, so as to point HL to the passwords.

598B

BIT 2,D

Test Bit Number 2 of Register D to see if the update password needs to be changed.

598D

JR Z,NOUPD
[5999H]

If the Z FLAG (Zero) is set then it does NOT need a change, so JUMP to 5999H.

If we are here, then we need to update the UPDATE PASSWORD.

598F

LD A,(UPDTDC)

Fetch the value stored at memory location 514CH and put it into Register A.
NOTE: 514CH is the storage location for the UPDATE PASSWORD.

5992

LD (HL),A

Store the value held in Register A (i.e., part of the UPDATE PASSWORD hash) into the memory location pointed to by Register Pair HL (i.e., the first byte of the UPDATE PASSWORD in the directory entry).

5993

LD A,(UPDTD + 1)

Fetch the value stored at memory location 514DH and put it into Register A.
NOTE: 514DH is the storage location for the 2nd byte of the UPDATE PASSWORD.

5996

INC HL

INCrement the value stored in Register Pair HL (i.e., the first byte of the UPDATE PASSWORD in the directory entry) by 1.

5997

LD (HL),A

Store the value held in Register A (i.e., the 2nd byte of the UPDATE PASSWORD) into the memory location pointed to by Register Pair HL (i.e., the second byte of the UPDATE PASSWORD in the directory entry).

5998

DEC HL

DECrement the value stored in Register Pair HL (i.e., the 2nd byte of the UPDATE PASSWORD) by 1.

“NOUPD”
5999

INC HL

INCrement the value stored in Register Pair HL (i.e., the 1st byte of the UPDATE PASSWORD in the directory entry) by 1.

599A

INC HL

INCrement the value stored in Register Pair HL (i.e., the 2nd byte of the UPDATE PASSWORD in the directory entry) by 1. Register Pair HL will now point to the first byte of the ACCESS PASSWORD in the directory entry.

599B

BIT 1,D

Test Bit Number 1 of Register D to see if the ACCESS password needs to be changed.

599D

JR Z,SAVE2
[59A8H]

If the Z FLAG (Zero) is set then it does NOT need a change, so JUMP to 59A8H.

599F

LD A,(ACCTDC)

Fetch the value stored at memory location 514EH and put it into Register A.
NOTE: 514EH is the storage location for the 1st byte of the ACCESS PASSWORD.

59A2

LD (HL),A

Store the value held in Register A (i.e., part of the ACCESS PASSWORD hash) into the memory location pointed to by Register Pair HL (i.e., the first byte of the ACCESS PASSWORD in the directory entry).

59A3

LD A,(ACCTDC + 1)

Fetch the value stored at memory location 514FH and put it into Register A.
NOTE: 514FH is the storage location for the 2nd byte of the ACCESS PASSWORD.

59A6

INC HL

INCrement the value stored in Register Pair HL by 1 so that HL will point to the second byte of the ACCESS PASSWORD in the directory entry.

59A7

LD (HL),A

Store the value held in Register A (i.e., the 2nd byte of the ACCESS PASSWORD) into the memory location pointed to by Register Pair HL (i.e., the second byte of the ACCESS PASSWORD in the directory entry).

“SAVE2”
59A8

CALL WRDIR
[4A7BH]

GOSUB to 4A7BH.
NOTE: 4A7BH is the SYS00/SYS routine to to write the directory entry from the copy in RAM to the diskette.

59AB

JP NZ,ERR
[6132H]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned because of an ERROR, JUMP to 6132H.

59AE

RET

RETurn to the caller.

59AFH – MESSAGE AND RAM STORAGE AREA for the “ATTRIB” Command.

“INDEX”
59AF

DEFM …

“EX“.

59B1

DEFM …

“RE“.

59B3

DEFM …

“WR“.

59B5

DEFM …

7E 7E.

59B7

DEFM …

“NA“.

59B9

DEFM …

“KI“.

59BB

DEFM …

“FU“.

59BDH – Part of the “DUMP” Command. Tests the validity of a HEXIDECIMAL NUMBER stored in Register A.

“LEGAL”
59BF

CP 30H

Compare the value held in Register A against a 0. Results:

If Register A equals 0, the Z FLAG is set.
If A < 0, the CARRY FLAG will be set.
if A >= 0, the NO CARRY FLAG will be set.

59BF

RET C

If A < 0, then A is not numeric (on the low side) and the C FLAG (Carry) is set. RETurn to the caller with the CARRY FLAG set to indicate an error (in this case, the character as below a 0).

59C0

CP 3AH

Compare the value held in Register A against 3AH (ASCII: 1 more than 9). Results:

If Register A equals 1 more than 9, the Z FLAG is set.
If A < 1 more than 9, the CARRY FLAG will be set.
if A >= 1 more than 9, the NO CARRY FLAG will be set.

59C2

CCF

Invert the state of the CARRY FLAG.

59C3

RET NC

If A < 1 more than 9 then the NC FLAG (No Carry) is set, RETurn to the caller.

59C4

CP 41H

Compare the value held in Register A against 41H (ASCII: A). Results:

If Register A equals A, the Z FLAG is set.
If A < A, the CARRY FLAG will be set.
if A >= A, the NO CARRY FLAG will be set.

59C6

RET C

If A < A then the the C FLAG (Carry) is set, RETurn to the caller.

59C7

CP 47H

Compare the value held in Register A against 47H (ASCII: 1 more than F). Results:

If Register A equals 1 more than F, the Z FLAG is set.
If A < 1 more than F, the CARRY FLAG will be set.
if A >= 1 more than F, the NO CARRY FLAG will be set.

59C9

CCF

Invert the state of the CARRY FLAG.

59CA

RET

RETurn to the caller with CARRY FLAG set if there is an error.

59CBH – Part of the “DUMP” Command. Tests the validity of an ALPHA NUMERIC character stored in Register A.

“LEAL”
59CB

CP 30H

Compare the value held in Register A against a 0. Results:

If Register A equals 0, the Z FLAG is set.
If A < 0, the CARRY FLAG will be set.
if A >= 0, the NO CARRY FLAG will be set.

59CD

RET C

If A < 0, then A is below numeric and the C FLAG (Carry) is set. RETurn to the caller with the CARRY FLAG set to indicate an error (in this case, the character as below a 0).

59CE

CP 3AH

Compare the value held in Register A against 3AH (ASCII: 1 more than 9). Results:

If Register A equals 1 more than 9, the Z FLAG is set.
If A < 1 more than 9, the CARRY FLAG will be set.
if A >= 1 more than 9, the NO CARRY FLAG will be set.

59D0

CCF

Invert the state of the CARRY FLAG.

59D1

RET NC

If A < 1 more than 9 then the NC FLAG (No Carry) is set, RETurn to the caller.

59D2

CP 41H

Compare the value held in Register A against 41H (ASCII: A). Results:

If Register A equals A, the Z FLAG is set.
If A < A, the CARRY FLAG will be set.
if A >= A, the NO CARRY FLAG will be set.

59D4

RET C

If the C FLAG (Carry) is set, RETurn to the caller.

59D5

CP 5BH

Compare the value held in Register A against 5BH (ASCII: 1 more than Z). Results:

If Register A equals 1 more than Z, the Z FLAG is set.
If A < 1 more than Z, the CARRY FLAG will be set.
if A >= 1 more than Z, the NO CARRY FLAG will be set.

59D7

CCF

Invert the state of the CARRY FLAG.

59D8

RET

RETurn to the caller with CARRY FLAG set if there is an error.

59D9H – “DIR” command.

“DIR”
59D9

LD BC,0000H

LET Register Pair BC = 0000H so that we can zero out a bunch of options.

59DC

LD (SYS),BC

Store the value held in Register BC (i.e., 0000) into the memory location 5AA5H (i.e., the byte flag for SYSTEM FILES).

59E0

LD (S6INV),BC

Store the value held in Register BC (i.e., 0000) into the memory location 5AB3H (i.e., the byte flag for INVISIBLE FILES).

59E4

LD (LPFLAG),BC

Store the value held in Register BC (i.e., 0000) into the memory location 5A4DH (i.e., the byte flag for PRINTER).

59E8

XOR A

Set Register A to ZERO and clear all Flags.

59E9

LD (S6DLFN),A

Store the value held in Register A (i.e., 0) into the memory location 5A69H, which is in the middle of an OPCODE and which will be holding the Logical File Number.

59EC

LD A,(HL)

Fetch the value stored at memory location pointed to by Register Pair HL (i.e., the pointer to the current position on the command line which was entered) and put it into Register A.

59ED

CP 3AH

Compare the value held in Register A against 3AH (ASCII: :) to look for a drive number parameter. Results: If Register A equals :, the Z FLAG is set; otherwise the NZ FLAG is set.

59EF

JR NZ,NODRV2
[5A06H]

If there was no : then the NZ FLAG (Not Zero) is set. With this, we can skip anything regarding a drive number parameter so JUMP to 5A06H.

59F1

INC HL

INCrement the value stored in Register Pair HL (i.e., the pointer to the current position on the command line which was entered) by 1.

59F2

LD A,(HL)

Fetch the value stored at memory location pointed to by Register Pair HL (i.e., the pointer to the current position on the command line which was entered) and put it into Register A. Since we had a :, we need Register A to hold a drive number for that parameter to be valid. .

59F3

SUB 30H

59F5

JP C,ERR9
[5234H]

If the C FLAG (Carry) is set, then taking 30H away from Register A caused a CARRY operation, meaning that the number was less than “0” so JUMP to 5234H.

59F8

CP TOPDRV

Compare the value held in Register A against 04H, which would be 1 + the highest possible drive number for TRSDOS v1.3. Results:

If Register A equals 1 more than 3.
If A < 1 more than 3, the CARRY FLAG will be set.
if A >= 1 more than 3, the NO CARRY FLAG will be set.

59FA

JP NC,ERR9
[5234H]

If A >= 1 more than 3 the NC FLAG (No Carry) is set and then we have a bad drive number, JUMP to 5234H.

59FD

LD C,A

If we are still here, then we had a number between 0-3 inclusive in Register A. Save that into Register C.

59FE

LD A,(MAXDRV)

Fetch the value stored at memory location 4413H and put it into Register A.
NOTE: 4413H is the storage location for the NUMBER OF DISK DRIVES in the system.

5A01

CP C

Compare the value held in Register A against the value held in Register C to see if the drive number we were given (i.e., Register C) is one of the valid drives on the system (i.e., Register A). Results:

If Register A equals Register C, the Z FLAG is set.
If A < Register C, the CARRY FLAG will be set.
if A >= Register C, the NO CARRY FLAG will be set.

5A02

JP C,ERR9
[5234H]

If Register A (i.e., NUMBER OF DISK DRIVES in the system) < Register C (i.e., the drive number we were given) then the C FLAG (Carry) is set, JUMP to 5234H.

5A05

INC HL

INCrement the value stored in Register Pair HL (i.e., the pointer to the current position on the command line which was entered) by 1.

“NODRV2”
5A06

PUSH BC

Save Register Pair BC (i.e., the drive number) to the top of the stack.

5A07

LD A,C

LET Register A = Register C (i.e., the drive number).

5A08

ADD A,30H

LET Register A = Register A + 30H. Note: Adding 30H to from Register A will convert decimal number 0-9 into its ASCII equivalent (i.e., 6 + 30H = 36H, which, in ASCII, is 6.

5A0A

LD (DRV2),A

Store the value held in Register A into the memory location 5C50H which is the message storage location for the DIR command header text.

5A0D

LD DE,SWTCH3

LET Register Pair DE = 5CC3H, which is the FCB in RAM.

5A10

CALL SWITCH
[4454H]

GOSUB to 4454H.
NOTE: 4454H is the DOS PARAMETER STRING PARSE routine. It decodes DOS LIBRARY parameters.

5A13

POP BC

Put the value held at the top of the STACK (i.e., the drive number) into Restore Register Pair BC, and then remove the entry from the stack.

5A14

JP NZ,ERR2
[5214H]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned because of an ERROR, JUMP to 5214H.

5A17

PUSH BC

Save Register Pair BC (i.e., the drive number) to the top of the stack.

5A18

CALL RDGAT
[4A93H]

GOSUB to 4A93H.
NOTE: 4A93H is the SYS00/SYS routine to READ THE GAT sector into RAM (Buffer at 4D00H).

5A1B

POP BC

Put the value held at the top of the STACK (i.e., the drive number) into Restore Register Pair BC, and then remove the entry from the stack.

5A1C

JP NZ,ERR
[6132H]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned because of an ERROR, JUMP to 6132H.

5A1F

PUSH BC

Save Register Pair BC (i.e., the drive number) to the top of the stack.

5A20

LD HL,BUFF2 + DID

LET Register Pair HL = 4DD0H which is the pointer to the DISKETTE NAME.

5A23

LD DE,DSKN2

LET Register Pair DE = 5C3DH which the location of the DISKETTE NAME in the on the printout.

5A26

LD BC,0008H

LET Register Pair BC = 0008H since there are 8 characters in a DISK NAME.

5A29

LDIR

5A2B

LD DE,DATE2

LET Register Pair DE = 5C5CH which the location of the DISKETTE DATE in the on the printout Note that HL is already pointing to where we would want to point HL.

5A2E

LD BC,0008H

LET Register Pair BC = 0008H since there are 8 characters in a DISK DATE.

5A31

LDIR

5A33

POP BC

Put the value held at the top of the STACK into Restore Register Pair BC, and then remove the entry from the stack.

5A34

PUSH BC

Save Register Pair BC (i.e., the drive number) to the top of the stack.

5A35

CALL RDHIT
[4ABAH]

GOSUB to 4ABAH.
NOTE: 4ABAH is the SYS00/SYS routine to read the HIT sector into RAM.

5A38

POP BC

Put the value held at the top of the STACK (i.e., the drive number) into Restore Register Pair BC, and then remove the entry from the stack.

5A39

JP NZ,ERR
[6132H]

If the NZ FLAG (Not Zero) is set, JUMP to 6132H.

5A3C

PUSH BC

Save Register Pair BC to the top of the stack.

5A3D

LD HL,BUFF1

LET Register Pair HL = 4300H which is DOS BUFFER NUMBER 1.

5A40

LD DE,BUFF2

LET Register Pair DE = 4D00H which is DOS BUFFER NUMBER 2.

5A43

LD (PNTBUF),DE

Store the value held in Register DE (i.e., the pointer to DOS BUFFER NUMBER 2) into the memory location 5A88H.

5A47

LD BC,0100H

LET Register Pair BC = 0100H (Decimal: 256) to signif that we are moving 256 bytes from DOS BUFFER 1 to DOS BUFFER 2.

5A4A

LDIR

5A4C

LD BC,LPFLAG

LET Register Pair BC = the value stored in 5A4DH which was placed here by this overlay. This is the PRINT flag.

5A4F

CALL CLS
[01C9H]

GOSUB to 01C9H which is the Model III ROM ROUTINE to CLEAR THE SCREEN and RETurn.

“CONT2”
5A52

LD HL,TITL4

LET Register Pair HL = 5C32H which is the message pointer to the first DIR output title line.

5A55

CALL PRT2
[6147H]

GOSUB to 6147H to either display or print the message pointed to by Register Pair HL.

5A58

LD HL,5C65H

LET Register Pair HL = 5C65H which is the message pointer to the second DIR output title line.

5A5B

CALL PRT2
[6147H]

GOSUB to 6147H to either display or print the message pointed to by Register Pair HL.

5A5E

POP BC

Put the value held at the top of the STACK (i.e., the drive number) into Restore Register Pair BC, and then remove the entry from the stack.

5A5F

LD A,C

LET Register A = Register C (i.e., the drive number).

5A60

LD (S6DDRV),A

Store the value held in Register A (i.e., the drive number) into the memory location 5A6BH which is in the middle of a LD B,nnH opcode.

5A63

LD A,02H

LET Register A = 02H since we have printed/displayed two lines already.

5A65

LD (SCRLCT),A

Store the value held in Register A into the memory location 4214H so as to protect those 2 lines.

“NXTREC”
5A68

LD B,S6DLFN

LET Register B = the value placed in 5A69H elsewhere in this overlay. This is the current file number.

5A6A

LD C,00H

LD C,nnH

LET Register C = the value placed in 5A6BH elsewhere in this overlay. This is the drive number.

5A6C

LD A,RECSEC

LET Register A = 05H, as the number of bytes to move to the next directory sector.

5A6E

ADD A,B

LET Register A = 05H + the current file number (held in Register B).

5A6F

CP MAXFIL + RECSEC

Compare the value held in Register A against 55H to see if we are past the end of the directory. Results:

If Register A equals 55H, the Z FLAG is set.
If A < 55H, the CARRY FLAG will be set.
if A >= 55H, the NO CARRY FLAG will be set.

5A71

JP NC,ENDIFL
[5BF5H]

If A >= 55H then the the NC FLAG (No Carry) will be set and we ARE past the end of the directory, so JUMP to 5BF5H.

5A74

LD (S6DLFN),A

Store the value held in Register A (i.e., the logical file number) into the memory location 5A69H.

5A77

CALL RDDIR
[4A67H]

GOSUB to 4A67H.
NOTE: 4A67H is the SYS00/SYS routine to read the directory entry into RAM (Buffer at 4300H).

5A7A

JP NZ,ERR
[6132H]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned because of an ERROR, JUMP to 6132H.

5A7D

CALL BRKCHK
[028DH]

GOSUB to 028DH.
NOTE: 028DH is the Model III ROM routine to CHECK FOR BREAK. On exit, the NZ FLAG will be set if BREAK was detected.

5A80

JP NZ,ABORT
[4030H]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned with a BREAK, JUMP to 4030H.
NOTE: 4030H is the OPERATION ABORTED routine. Routine runs, displays an error, and returns to the DOS PROMPT.

5A83

LD HL,BUFF1

LET Register Pair HL = 4300H, which is the DIRECTORY SECTOR BUFFER in RAM.

“L6OP21”
5A86

PUSH HL

Save Register Pair HL (i.e., the current pointer in the DIRECTORY SECTOR BUFFER in RAM) to the top of the stack.

5A87

LD HL,PNTBUF

LET Register Pair HL = the value placed in 5A88H-5A89H elsewhere in this overlay. This would be the HASH TABLE ENTRY.

5A8A

LD A,(HL)

Fetch the value stored at memory location pointed to by Register Pair HL (i.e., the hash code) and put it into Register A.

5A8B

INC HL

INCrement the value stored in Register Pair HL (i.e., the current pointer in the DIRECTORY SECTOR BUFFER in RAM) by 1.

5A8C

LD (PNTBUF),HL

Store the value held in Register HL into the memory location 5A88H (i.e., HASH TABLE ENTRY).

5A8F

OR A

Set FLAGS based on the contents of Register A so as to check to see if that hash table entry is active or not.

5A90

JP Z,NXTFIL
[5BE7H]

If the Z FLAG (Zero) is set then the table entry is not active, so we don’t need to display it. SKIP to 5BE7H.

5A93

POP HL

Put the value held at the top of the STACK (i.e., the current pointer in the DIRECTORY SECTOR BUFFER in RAM) into Restore Register Pair HL, and then remove the entry from the stack.

5A94

LD A,(HL)

Fetch the value stored at memory location (i.e., the FILE TYPE BYTE) pointed to by Register Pair HL (i.e., the current pointer in the DIRECTORY SECTOR BUFFER in RAM) and put it into Register A.

5A95

PUSH HL

Save Register Pair HL (i.e., the current pointer in the DIRECTORY SECTOR BUFFER in RAM, currently pointing at the FILE TYPE BYTE) to the top of the stack.

5A96

BIT 7,A

Test Bit Number 7 of Register A to see if this is an EXTENDED DIRECTORY ENTRY. Z FLAG will be set if that bit is 0, and NZ FLAG will be set if that bit is 1.

5A98

JP NZ,NXTFIL
[5BE7H]

If the NZ FLAG (Not Zero) is set then this is an EXTENDED DIRECTORY ENTRY, in which case we do not want to display it. SKIP to 5BE7H.

5A9B

BIT 4,A

Test Bit Number 4 of Register A to see if this is an ACTIVE PRIMARY FILE ENTRY. Z FLAG will be set if that bit is 0, and NZ FLAG will be set if that bit is 1.

5A9D

JP Z,NXTFIL
[5BE7H]

If the Z FLAG (Zero) is set then this is an ACTIVE PRIMARY FILE ENTRY, in which case we do not want to display it. SKIP to 5BE7H.

5AA0

BIT 6,A

Test Bit Number 6 of Register A to see if this is a SYSTEM FILE. Z FLAG will be set if that bit is 0 and the file is NOT a SYSTEM FILE, and NZ FLAG will be set if that bit is 1 and the file is a SYSTEM FILE.

5AA2

JR Z,NOSYS
[5AAEH]

If the Z FLAG (Zero) is set then this is not a SYSTEM FILE, in which case we ABSOLUTELY are ready to display this entry, so SKIP to 5AAEH.

5AA4

LD DE,SYS

LET Register Pair DE = the contents of 5AA5H which was placed here elsewhere in this overlay. This is the DISPLAY SYSTEM FILE flag.

5AA8
5AA7

LD A,D
OR E

5AA9

JP Z,NXTFIL
[5BE7H]

If the Z FLAG (Zero) is set then were NOT asked to display SYSTEM FIELS, so JUMP to 5BE7H.

5AAC

JR NOTINV
[5ABAH]

JUMP to 5ABAH to display the file entry, 1 space, and the extension.

5AAEH – Continuation of the “DIR” Command. Jumped here when we have passed the first filtering hurdles and the directory entry being pointed to has still not yet been disqualified from being displayed.

NOSYS
5AAE

BIT 3,A

Test Bit Number 3 of Register A to see if the file is INVISIBLE. Z FLAG will be set if that bit is 0, and NZ FLAG will be set if that bit is 1.

5AB0

JR Z,NOTINV
[5ABAH]

If the Z FLAG (Zero) is set then the file is visible, then we can skip the test for invisible file display and JUMP to 5ABAH.

5AB2

LD DE,S6INV

LET Register Pair DE = the memory contents of 4AB3H-4AB4H, which is the flag for whether TRSDOS was asked to display invisible files.

5AB5
5AB6

LD A,D
OR E

5AB7

JP Z,NXTFIL
[5BE7H]

If the Z FLAG (Zero) is set then we were NOT asked to display invisible files, so JUMP to 5BE7H.

5ABAH – Continuation of the “DIR” Command. Display the filespec, 1 space, and the extension.

“NOTINV”
5ABA

PUSH HL

Save Register Pair HL (i.e., the current pointer in the DIRECTORY SECTOR BUFFER in RAM, currently pointing at the FILE TYPE BYTE) to the top of the stack.

5ABB

INC HL

INCrement the value stored in Register Pair HL (i.e., the current pointer in the DIRECTORY SECTOR BUFFER in RAM, currently pointing at the FILE TYPE BYTE) by 1 (to point to the file CREATION MONTH).

5ABC

LD A,(HL)

Fetch the value stored at memory location pointed to by Register Pair HL (i.e., the file CREATION MONTH) and put it into Register A.

5ABD

LD (SAVMTH),A

Store the value held in Register A (i.e., the file CREATION MONTH) into the memory location 5BCCH which is in the middle of an OPCODE.

5AC0

INC HL

INCrement the value stored in Register Pair HL (i.e., the current pointer in the DIRECTORY SECTOR BUFFER in RAM, currently pointing at the FILE CREATION MONTH) by 1 (to point to the file CREATION MONTH).

5AC1

LD A,(HL)

Fetch the value stored at memory location (i.e., the file CREATION MONTH) pointed to by Register Pair HL (i.e., the current pointer in the DIRECTORY SECTOR BUFFER in RAM, currently pointing at the FILE CREATION MONTH) and put it into Register A.

5AC2

LD (SAVYR),A

Store the value held in Register A into the memory location 5BD4H which is in the middle of an OPCODE.

5AC5

POP HL

Put the value held at the top of the STACK (i.e., the current pointer in the DIRECTORY SECTOR BUFFER in RAM, currently pointing at the FILE TYPE BYTE) into Restore Register Pair HL, and then remove the entry from the stack.

5AC7
5AC6
5AC9

LD A,L
ADD A,DNAME
LD L,A

LET Register L = Register L + 05H.

5ACA

PUSH HL

Save Register Pair HL (i.e., the current pointer in the DIRECTORY SECTOR BUFFER in RAM, currently pointing at the FILENAME) to the top of the stack.

5ACB

LD B,08H

LET Register B = 08H since the FILENAME has 8 characters.

“L6OP16”
5ACD

LD A,(HL)

Fetch the value stored (i.e., a character of the filename) at memory location pointed to by Register Pair HL (i.e., the current pointer in the DIRECTORY SECTOR BUFFER in RAM, currently pointing at the FILENAME) and put it into Register A.

5ACE

CP 20H

Compare the value held in Register A (i.e., a character of the filename) against 20H (ASCII: SPACE). Results: If Register A equals SPACE, the Z FLAG is set; otherwise the NZ FLAG is set.

5AD0

JR Z,YESSPC
[5AD8H]

If we have a SPACE then the Z FLAG (Zero) is set. We will take this as the end of the filename, so JUMP to 5AD8H.

5AD2

INC HL

INCrement the value stored in Register Pair HL (i.e., the current pointer in the DIRECTORY SECTOR BUFFER in RAM, currently pointing a character in the FILENAME) by 1.

5AD3

CALL PDATA
[6135H]

GOSUB to 6135H to display or print the byte held in Register A (i.e., a character of the filename); routine affects Registers A and E.

5AD6

DJNZ L6OP16
[5ACDH]

LOOP back to 5ACDH, reducing Register B each time, and continue to LOOP until Register B has been reduced to ZERO, in which case, continue with the next instruction.

“YESSPC”
5AD8

POP HL

Put the value held at the top of the STACK (i.e., the current pointer in the DIRECTORY SECTOR BUFFER in RAM, currently pointing at the FILENAME) into Restore Register Pair HL, and then remove the entry from the stack.

5AD9

PUSH DE

Save Register Pair DE to the top of the stack.

5ADA

LD DE,0008H

LET Register Pair DE = 0008H to skip the 8 bytes of the filename to now point to the FILE EXTENSION.

5ADD

ADD HL,DE

LET Register Pair HL = Register Pair HL (i.e., the current pointer in the DIRECTORY SECTOR BUFFER in RAM, currently pointing at the FILENAME) + Register Pair DE (8 bytes).

5ADE

POP DE

Put the value held at the top of the STACK into Restore Register Pair DE, and then remove the entry from the stack.

5ADF

LD B,03H

LET Register B = 03H, which is the maximum number of characters in an extension.

5AE1

LD A,(HL)

Fetch the value stored at memory location pointed to by Register Pair HL (i.e., the current pointer in the DIRECTORY SECTOR BUFFER in RAM, currently pointing at the EXTENSION) and put it into Register A.

5AE2

CP 20H

Compare the value held in Register A (i.e., a character of the EXTENSION) against 20H (ASCII: SPACE). Results: If Register A equals SPACE, the Z FLAG is set; otherwise the NZ FLAG is set.

5AE4

JR Z,ENDEXT
[5AF6H]

If we have a SPACE then the Z FLAG (Zero) is set. We will take this as the end of the EXTENSION, so JUMP to 5AF6H.

5AE6

LD A,2FH

LET Register A = 2FH (ASCII: /) as the extension delimiter.

5AE8

CALL PDATA
[6135H]

GOSUB to 6135H to display or print the /; routine affects Registers A and E.

“L6OP18”
5AEB

LD A,(HL)

Fetch the value stored at memory location (i.e., a character of the EXTENSION) pointed to by Register Pair HL (i.e., the current pointer in the DIRECTORY SECTOR BUFFER in RAM, currently pointing at the EXTENSION) and put it into Register A.

5AEC

CP 20H

Compare the value held in Register A against 20H (ASCII: SPACE). Results: If the character held in Register A equals SPACE, the Z FLAG is set; otherwise the NZ FLAG is set.

5AEE

JR Z,ENDEXT
[5AF6H]

If the character held in Register A equals SPACE then the Z FLAG (Zero) is set, and we have reached the end of the EXTENSION. JUMP to 5AF6H.

5AF0

INC HL

INCrement the value stored in Register Pair HL (i.e., the current pointer in the DIRECTORY SECTOR BUFFER in RAM, currently pointing at the EXTENSION) by 1.

5AF1

CALL PDATA
[6135H]

GOSUB to 6135H to display or print the character held in Register A; routine affects Registers A and E.

5AF4

DJNZ L6OP18
[5AEBH]

LOOP back to 5AEBH for all 3 characters of the extension, reducing Register B each time, and continue to LOOP until Register B has been reduced to ZERO, in which case, continue with the next instruction.

5AF6H – Continuation of the “DIR” Command. Position the Cursor to the Right Location.

“ENDEXT”
5AF6

LD A,(CURSOR)

Fetch the value stored at memory location 4020H (i.e., the cursor position on screen) and put it into Register A.

The next set of instructions calculates how many spaces to tab over on the screen.

5AF9

AND 3FH

MASK the value of Register A against 3FH (0011 1111). This has the effect of turning off bits 7, 6, leaving only bits 5, 4, 3, 2, 1, 0, which is the column on the screen, active.

5AFB

NEG

Rather than SUBTRACTING, we are going to ADD, so turn Register A negative.

5AFD

ADD A,0FH

LET Register A = Register A + 0FH.

5AFF

LD B,A

LET Register B = Register A.

“ENDEX1”
5B00

LD A,20H

LET Register A = 20H (ASCII: SPACE).

5B02

CALL PDATA
[6135H]

GOSUB to 6135H to display or print the character held in Register A; routine affects Registers A and E.

5B05

DJNZ ENDEX1
[5B00H]

LOOP back to 5B00H, reducing Register B each time, and continue to LOOP until Register B has been reduced to ZERO, in which case, continue with the next instruction.

5B07H – Continuation of the “DIR” Command. Display NON-INV, INV, or SYS FILE

5B07

DEC L

DECrement the value stored in Register L (i.e., the last character of the EXTENSION) by 1.

5B08

LD A,L

LET Register A = Register L (i.e., the last character of the EXTENSION).

5B09

AND 0F0H

MASK the value of Register A against 0F0H (1111 0000). This has the effect of turning off bits 3, 2, 1, 0 and positions HL to the start of the directory entry.

5B0B

LD L,A

LET Register L = Register A.

5B0C

LD B,(HL)

Fetch the value stored at memory location pointed to by Register Pair HL (i.e., the FILE TYPE byte of the DIRECTORY SECTOR in RAM) and put it into Register B.

5B0D

LD A,49H

LET Register A = 49H (ASCII: I).

5B0F

BIT 3,B

Test Bit Number 3 of Register A to see if the file is INVISIBLE. Z FLAG will be set if that bit is 0 (and the file is VISIBLE), and NZ FLAG will be set if that bit is 1 (and the file is INVISIBLE).

5B11

JR NZ,Y1
[5B15H]

If the NZ FLAG (Not Zero) is then file is invisible, so skip over the instruction that changes the output flag to “N” (so it stays “I”) and JUMP to 5B15H.

5B13

LD A,4EH

LET Register A = 4EH (ASCII: N).

“Y1”
5B15

CALL PDATA
[6135H]

GOSUB to 6135H to display or print the character held in Register A; routine affects Registers A and E.

5B18

BIT 6,B

Test Bit Number 6 of Register B to see if this is a SYSTEM FILE. Z FLAG will be set if that bit is 0 and the file is NOT a SYSTEM FILE, and NZ FLAG will be set if that bit is 1 and the file is a SYSTEM FILE.

5B1A

LD A,53H

LET Register A = 53H (ASCII: S).

5B1C

JR NZ,Y2
[5B20H]

If the NZ FLAG (Not Zero) is set, then the file is a SYSTEM FILE, so we want to keep the “S” in Register A. JUMP to 5B20H.

5B1E

LD A,2AH

LET Register A = 2AH (ASCII: *).

“Y2”
5B20

CALL PDATA
[6135H]

GOSUB to 6135H to display or print the character held in Register A; routine affects Registers A and E.

5B23H – Continuation of the “DIR” Command. Display the PROTECTION (U)PDATE, A(CCESS), or B(OTH) UPDATE AND ACCESS

5B23

PUSH HL

Save Register Pair HL (i.e., pointer to the FILE TYPE byte of the DIRECTORY SECTOR in RAM) to the top of the stack.

5B25
5B24
5B27

LD A,L
ADD A,DUPD
LD L,A

LET Register L = Register L + 10H.

5B28

LD E,(HL)

Fetch the value stored at memory location (i.e., the 1st character of the UPDATE PASSWORD byte of the DIRECTORY SECTOR in RAM) pointed to by Register Pair HL (i.e., the pointer to the 1st character of the UPDATE PASSWORD byte of the DIRECTORY SECTOR in RAM) and put it into Register E.

5B29

INC HL

INCrement the value stored in Register Pair HL (i.e., the pointer to the 2nd character of the UPDATE PASSWORD byte of the DIRECTORY SECTOR in RAM) by 1.

5B2A

LD D,(HL)

Fetch the value stored at memory location (i.e., the 2nd character of the UPDATE PASSWORD byte of the DIRECTORY SECTOR in RAM) pointed to by Register Pair HL (i.e., pointer to the 2nd character of the UPDATE PASSWORD of the DIRECTORY SECTOR in RAM) and put it into Register D.

5B2B

PUSH HL

Save Register Pair HL (i.e., pointer to the 2nd character of the UPDATE PASSWORD of the DIRECTORY SECTOR in RAM) to the top of the stack.

5B2C

LD HL,MASTPW

LET Register Pair HL = 5CEFH which would be a blank password.

5B2F

SBC HL,DE

Subtracts the value stored in Register Pair DE (i.e., the 2-Byte UPDATE PASSWORD byte of the DIRECTORY SECTOR in RAM) and the carry flag from the value stored in Register Pair HL (i.e., 5CEFH).

5B31

POP HL

Put the value held at the top of the STACK (i.e., pointer to the 2nd character of the UPDATE PASSWORD of the DIRECTORY SECTOR in RAM) into Restore Register Pair HL, and then remove the entry from the stack.

5B32

LD A,55H

LET Register A = 55H (ASCII: U). If displayed, this would indicatate that the file is protected by an UPDATE PASSWORD.

5B34

JR NZ,ACC
[5B38H]

If the NZ FLAG (Not Zero) is set, then the password is NOT blank, so JUMP to 5B38H.

5B36

LD A,58H

LET Register A = 58H (ASCII: X). If displayed, this would indicatate that the file is protected by an ACCESS PASSWORD.

“ACC”
5B38

INC L

INCrement the value stored in Register L (i.e., LSB of the pointer to the 2nd character of the UPDATE PASSWORD of the DIRECTORY SECTOR in RAM) by 1 so that HL will now point to the ACCESS PASSWORD.

5B39

LD E,(HL)

Fetch the value stored at memory location (i.e., the 1st character of the ACCESS PASSWORD byte of the DIRECTORY SECTOR in RAM) pointed to by Register Pair HL (i.e., the pointer to the 1st character of the ACCESS PASSWORD byte of the DIRECTORY SECTOR in RAM) and put it into Register E.

5B3A

INC HL

INCrement the value stored in Register Pair HL (i.e., the pointer to the 1st character of the ACCESS PASSWORD byte of the DIRECTORY SECTOR in RAM) by 1.

5B3B

LD D,(HL)

Fetch the value stored at memory location (i.e., the 2nd character of the ACCESS PASSWORD byte of the DIRECTORY SECTOR in RAM) pointed to by Register Pair HL (i.e., pointer to the 2nd character of the ACCESS PASSWORD of the DIRECTORY SECTOR in RAM) and put it into Register D.

5B3C

LD HL,MASTPW

LET Register Pair HL = 5CEFH which would be the hash for no password.

5B3F

OR A

Set FLAGS based on the contents of Register A.

5B40

SBC HL,DE

Subtracts the value stored in Register Pair DE (i.e., the 2-Byte ACCESS PASSWORD of the DIRECTORY SECTOR in RAM) and the carry flag from the value stored in Register Pair HL (i.e., 5CEFH).

5B42

JR Z,CONTY
[5B4BH]

If the Z FLAG (Zero) is set then the ACCESS PASSWORD is blank, so JUMP to 5B4BH.

5B44

CP 55H

Compare the value held in Register A against U. Results: If Register A equals U, the Z FLAG is set; otherwise the NZ FLAG is set.

5B46

LD A,41H

LET Register A = 41H (ASCII: A).

5B48

JR NZ,CONTY
[5B4BH]

If the NZ FLAG (Not Zero) is set then the file is NOT update protected, so JUMP to 5B4BH.

5B4A

INC A

INCrement the value stored in Register A by 1, so that A will now be a B to signify that the file is protected BOTH by an UPDATE and an ACCESS password.

“CONTY”
5B4B

CALL PDATA
[6135H]

GOSUB to 6135H to display or print the character held in Register A; routine affects Registers A and E.

5B4E

POP HL

Put the value held at the top of the STACK (i.e., the file pointer) into Restore Register Pair HL, and then remove the entry from the stack.

5B4FH – Continuation of the “DIR” Command. Display the PROTECTION NUMBER OF THE PROTECTION LEVEL.

5B4F

PUSH HL

Save Register Pair HL (i.e., the file pointer) to the top of the stack.

5B50

LD A,(HL)

Fetch the value stored at memory location pointed to by Register Pair HL (i.e., the FILE ACCESS LEVEL) and put it into Register A.

5B51

AND 07H

MASK the value of Register A against 07H (0000 0111). This has the effect of leaving only bits 2, 1, 0 active, which are the access level bits.

5B53

ADD A,30H

LET Register A = Register A + 30H. Note: Adding 30H to from Register A will convert decimal number 0-9 into its ASCII equivalent (i.e., 6 + 30H = 36H, which, in ASCII, is 6.

5B55

CALL PDATA
[6135H]

GOSUB to 6135H to display or print the character held in Register A; routine affects Registers A and E.

5B58H – Continuation of the “DIR” Command. Get the EOF Byte.

5B58
5B59
5B5A

INC L
INC L
INC L

INCrement the value stored in Register L by 3, so that Register Pair HL now points to the EOF byte of the DIRECTORY SECTOR in RAM.

5B5B

LD A,(HL)

Fetch the value stored at memory location (i.e., the the EOF byte of the DIRECTORY SECTOR in RAM) pointed to by Register Pair HL and put it into Register A.

5B5C

LD (S6EOF),A

Store the value held in Register A (i.e., the EOF byte of the DIRECTORY SECTOR in RAM) into the memory location 5B90H.

5B5FH – Continuation of the “DIR” Command. Get the LRL Byte.

5B5F

INC L

INCrement the value stored in Register L by 1, so that Register Pair HL now points to the Logical Record Length byte of the DIRECTORY SECTOR in RAM.

5B60

LD L,(HL)

Fetch the value stored at memory location (i.e., the LRL byte of the DIRECTORY SECTOR in RAM) pointed to by Register Pair HL and put it into Register L.

5B61

LD A,L

LET Register A = Register L (i.e., the LRL byte of the DIRECTORY SECTOR in RAM).

5B62

LD (LRL2),A

Store the value held in Register A (i.e., the LRL byte of the DIRECTORY SECTOR in RAM) into the memory location 5B89H.

5B65

SUB 01H

SUBtract the value 01H from Register A (i.e., the LRL byte of the DIRECTORY SECTOR in RAM) to set the flags.

5B67

LD A,00H

LET Register A = 00H to signify a 256 Byte LRL.

5B69

ADC A,00H

Add 00H to 00H to set the flags.

5B6B

LD H,A

LET Register H = Register A (i.e., 00H, to signify a 256 byte LRL).

5B6C

CALL BINDEC
[61C1H]

GOSUB to 61C1H to display the contents of Register Pair HL (i.e., the LRL for the file being processed) in decimal form.

5B6F

POP HL

Put the value held at the top of the STACK (i.e., the value that confused me in 5B4F) into Restore Register Pair HL, and then remove the entry from the stack.

5B70H – Continuation of the “DIR” Command. Calculate the number of records in a file.

5B71
5B70
5B73

LD A,L
ADD A,DERN
LD L,A

LET Register L = Register L + 14H, so that Register Pair HL now points to the END OF FILE SECTOR NUMBER byte of the DIRECTORY SECTOR in RAM.

5B74

LD E,(HL)

Fetch the value stored at memory location (i.e., the LSB of the END OF FILE SECTOR NUMBER byte of the DIRECTORY SECTOR in RAM) pointed to by Register Pair HL and put it into Register E.

5B75

INC L

INCrement the value stored in Register L by 1, so that Register Pair HL now points to the MSB of the END OF FILE SECTOR NUMBER byte of the DIRECTORY SECTOR in RAM.

5B76

LD D,(HL)

Fetch the value stored at memory location (i.e., the MSB of the END OF FILE SECTOR NUMBER byte of the DIRECTORY SECTOR in RAM) pointed to by Register Pair HL and put it into Register D. Now DE=HL=the END OF FILE SECTOR NUMBER byte of the DIRECTORY SECTOR in RAM.

5B77

PUSH HL

Save Register Pair HL (i.e., the pointer to the MSB of the END OF FILE SECTOR NUMBER byte of the DIRECTORY SECTOR in RAM) to the top of the stack.

5B78

LD A,(LRL2)

Fetch the value stored at memory location 5B89H (which is in the middle of an OPCODE and is curently storing the files LRL) and put it into Register A.

5B7B

OR A

Since a LD command does not set any FLAGS, Set FLAGS based on the contents of Register A.

5B7C

JR NZ,NLR256
[5B87H]

If LRL is not Zero (i.e., the LRL is not 256 bytes) then the NZ FLAG (Not Zero) will be set. JUMP to 5B87H.

5B7E

LD A,(S6EOF)

Fetch the value stored at memory location 5B90H (which is in the middle of an OPCODE and is curently storing the files EOF) and put it into Register A.

5B81

OR A

Since a LD command does not set any FLAGS, Set FLAGS based on the contents of Register A.

5B82

JR Z,LRL257
[5B98H]

If the EOF is zero, then the Z FLAG (Zero) is set. JUMP to 5B98H.

5B84

INC DE

INCrement the value stored in Register Pair DE (i.e., the END OF FILE SECTOR NUMBER) by 1.

5B85

JR LRL257
[5B98H]

JUMP to 5B98H to continue with this routine.

5B87H – Continuation of the “DIR” Library Command. Jumped here from 5B7CH if the LRL is not zero so that we can calculate the number of LRL for records other than a 256 LRL.

“NLR256”
5B87

EX DE,HL

EXchange the value stored in Register Pair HL (i.e., the pointer to the MSB of the END OF FILE SECTOR NUMBER byte of the DIRECTORY SECTOR in RAM) with the value stored in Register Pair DE (i.e., the END OF FILE SECTOR NUMBER byte of the DIRECTORY SECTOR in RAM).

5B88

LD A,LRL2

LET Register A = the memory contents opf 5B89, which is the files LRL, as was placed in this location elsewhere in this Overlay.

5B8A

CALL DIV
[4451H]

GOSUB to 4451H to divide HL by the LRL.

5B8D

LD H,A

LET Register H = Register A (i.e., the ( HL / LRL) * 256 + the EOF).

5B8E

LD D,L

LET Register D = Register L (i.e., the MSB of the number of records).

5B8F

LD L,S6EOF

LET Register L = the memory contents of 5B90, which is the files EOF, as was placed in this location elsewhere in this Overlay.

5B91

LD A,(LRL2)

Fetch the value stored at memory location 5B89H (i.e., the files LRL) and put it into Register A.

5B94

CALL DIV
[4451H]

GOSUB to 4451H to divide HL by the LRL again.

5B97

LD E,L

LET Register E = Register L so that Register Pair DE holds the number of records.

Next up we need to display the number of records in the file.

“LRL257”
5B98

EX DE,HL

EXchange the value stored in Register Pair HL with the value stored in Register Pair DE (i.e., the number of records, now held in HL).

5B99

CALL BINDEC
[61C1H]

GOSUB to 61C1H to display the contents of Register Pair HL (i.e., the number of records for the file being processed) in decimal form.

Next up we need to calculate the number of GRANS and EXTENT POINTERS in the file.

5B9C

POP HL

Put the value held at the top of the STACK (i.e., the pointer to the MSB of the END OF FILE SECTOR NUMBER byte of the DIRECTORY SECTOR in RAM) into Register Pair HL, and then remove the entry from the stack.

5B9D

INC L

INCrement the value stored in Register L by 1 so that Register Pair HL now points to the EXTENTS byte of the DIRECTORY SECTOR in RAM.

We are about to count up the grans by adding the gran numbers found in each valid extent. Register Pair DE will hold the number of grans and Register Pair BC will hold the number of extents.

5B9E

LD DE,0000H

LET Register Pair DE = 0000H.

5BA1

LD C,D

LET Register C = Register D.

5BA2

LD B,MAXEXT

LET Register B = 0DH (Decimal: 13) for a loop that will skip over the 13 extents.

“L6OP19”
5BA4

LD A,(HL)

Fetch the value stored at memory location (i.e., an extent byte) pointed to by Register Pair HL and put it into Register A.

5BA5

INC L

INCrement the value stored in Register L by 1 so that Register Pair HL now points to the GRAN byte of that valid EXTENT byte of the DIRECTORY SECTOR in RAM.

5BA6

CP 0FEH

Compare the value held in Register A against 0FEH, which would indicate if we have run out of EXTENT bytes. Results:

If Register A equals 0FEH, the Z FLAG is set.
If A < 0FEH, the CARRY FLAG will be set.
if A >= 0FEH, the NO CARRY FLAG will be set.

5BA8

JR NC,CONT4
[5BB6H]

If the extent byte in Register A equals 0FEH or 0FFH then the NC FLAG (No Carry) is set, and we have reached the end of the valid extent bytes. JUMP to 5BB6H.

5BAA

INC C

If we didn’t jump away, then we have a valid extent byte in Register A, so INCrement the value stored in Register C (which is counting the number of extents) by 1.

5BAB

LD A,(HL)

Fetch the value stored at memory location (i.e., the number of grans) pointed to by Register Pair HL and put it into Register A.

5BAC

INC L

INCrement the value stored in Register L by 1 so that Register Pair HL now points to the next EXTENT byte of the DIRECTORY SECTOR in RAM.

5BAD

AND 1FH

MASK the value of Register A (i.e., the number of grans in the extent) against 1FH (0001 1111). This has the effect of turning off bits 7, 6, 5, leaving only bits 4, 3, 2, 1, 0 active.

5BAF

ADD A,E

LET Register A = Register A + Register E (i.e., the total number of grans for the file).

5BB0

LD E,A

LET Register E = Register A (i.e., the total number of grans for the file).

5BB1

JR NC,CONT3
[5BB4H]

If the NC FLAG (No Carry) is set then we did NOT have an overflow, so skip the next couple of instructions (which deal with an overflow) to 5BB4H.

5BB3

INC D

INCrement the value stored in Register D (which is also tracking the number of grans, but on the MSB level) by 1.

“CONT3”
5BB4

DJNZ L6OP19
[5BA4H]

LOOP back to 5BA4H, reducing Register B each time, and continue to LOOP until Register B has been reduced to ZERO, in which case, continue with the next instruction.

5BB6H – Continuation of the “DIR” Command. Display the Number of GRANS in a File.

“CONT4”
5BB6

EX DE,HL

EXchange the value stored in Register Pair HL (i.e., the pointer to the EXTENT byte of the DIRECTORY SECTOR in RAM) with the value stored in Register Pair DE (i.e., the number of grans for the file).

5BB7

PUSH BC

Save Register Pair BC (i.e., the number of extents for the file being processed) to the top of the stack.

5BB8

CALL BINDEC
[61C1H]

GOSUB to 61C1H to display the contents of Register Pair HL (i.e., the number of extents for the file being processed) in decimal form.

5BBB

POP BC

Put the value held at the top of the STACK (i.e., the number of extents for the file being processed) into Restore Register Pair BC, and then remove the entry from the stack.

5BBCH – Continuation of the “DIR” Command. Display the Number of EXTENTS in a File.

5BBD
5BBC

LD L,C
LD H,00H

LET Register Pair HL = Register C (i.e., the number of extents in the file being processed).

5BBF

CALL BINDEC
[61C1H]

GOSUB to 61C1H to display the contents of Register Pair HL (i.e., the number of EXTENTS for the file being processed) in decimal form.

5BC2H – Continuation of the “DIR” Command. Display the EOF BYTE OFFSET of a File.

5BC2

LD A,(S6EOF)

Fetch the value stored at memory location 5B90H (i.e., the EOF byte of the file being processed) and put it into Register A.

5BC6
5BC5

LD L,A

LET Register Pair HL = Register A (i.e., the EOF BYTE of the file being processed).

5BC8

CALL BINDEC
[61C1H]

GOSUB to 61C1H to display the contents of Register Pair HL (i.e., the EOF BYTE of the file being processed) in decimal form.

5BCBH – Continuation of the “DIR” Command. Display the DATE OF CREATION for a File.

5BCB

LD A,SAVMTH

LET Register A = the memory contents of 5BCCH, which was placed here elsewhere in this Overlay. This is the file’s creation month.

5BCD

LD HL,MTH

LET Register Pair HL = 5CBDH, which is the pointer to the creation month in the MESSAGE STORAGE table for the DIR command.

5BD0

CALL HEXAAS
[61B5H]

GOSUB to 61B5H to convert the value.

5BD3

LD A,SAVYR

LET Register A = the memory contents of 5BD4H, which was placed here elsewhere in this Overlay. This is the file’s creation year.

5BD5

LD HL,YER

LET Register Pair HL = 5CC0H, which is the pointer to the creation year in the MESSAGE STORAGE table for the DIR command.

5BD8

CALL HECXAAS
[61B5H]

GOSUB to 61B5H to convert the value.

5BDB

LD HL,DETA

LET Register Pair HL = 5CBAH, which is the pointer to the date in the MESSAGE STORAGE table for the DIR command.

5BDE

CALL PRT2
[6147H]

GOSUB to 6147H to either display or print the message pointed to by Register Pair HL.

5BE1H – Continuation of the “DIR” Command. Check for a User HOLD Key.

“NO”
5BE1

CALL INKEY
[6167H]

GOSUB to 6167H to check the keyboard for a pause request.

5BE4

POP HL

Put the value held at the top of the STACK (I have NO idea what this might be) into Restore Register Pair HL, and then remove the entry from the stack.

5BE5

RET NZ

If the NZ FLAG (Not Zero) is set then we got a BREAK so we abort out and RETurn to the caller.

5BE6

PUSH HL

Save Register Pair HL to the top of the stack.

5BE6H – Continuation of the “DIR” Command. Bump to the next file in the directory.

“NXTFIL”
5BE7

POP HL

Put the value held at the top of the STACK into Restore Register Pair HL, and then remove the entry from the stack.

“NXTFI1”
5BE8

LD DE,SIZDIR

LET Register Pair DE = 0030H so that we can advance HL to point to the next directory entry. 30H is the size of one directory record.

5BEB

ADD HL,DE

LET Register Pair HL = Register Pair HL (i.e., the pointer to some byte in a directory entry) + Register DE (i.e., an offset from whatever that byte was to the beginning of the next directory entry).

5BEC

LD A,L

LET Register A = Register L so that we can test to see if that was the last directory entry in the sector.

5BED

CP 0F0H

Compare the value held in Register A against 0F0H (i.e., the LSB byte location in a sector where we have reached the end of the directory entries in that sector). Results: If Register A equals 0F0H, the Z FLAG is set; otherwise the NZ FLAG is set.

5BEF

JP Z,NXTREC
[5A68H]

If the Z FLAG (Zero) is set then we have a new sector to deal with so JUMP to 5A68H.

5BF2

JP L6OP21
[5A86H]

If we have not reached the end of the sector then LOOP BACK to 5A86H to keep processing directory entries.

5BF5H – Continuation of the “DIR” Command. All Files have been displayed. Calculate the number of FREE GRANS on the Dis.

“ENFILE”
5BF5

LD A,(S6DDRV)

Fetch the value stored at memory location 5A6BH (i.e., the drive number) and put it into Register A.

5BF8

LD C,A

LET Register C = Register A (i.e., the drive number).

5BF9

CALL RDGAT
[4A93H]

GOSUB to 4A93H.
NOTE: 4A93H is the SYS00/SYS routine to READ THE GAT sector into RAM (Buffer at 4D00H).

5BFC

LD IX,BUFF2

LET Register Pair IX = 4D00H, which is the pointer to the GAT SECTOR now in RAM.

5C00

LD HL,0000H

LET Register Pair HL = 0000H.

5C04
5C03

LD D,H
LD E,L

LET Register DE = Register HL.

5C05

LD C,MAXTRK

LET Register C = 28H (Decimal: 40) as there are 40 tracks on a TRSDOS v1.3 diskette.

“L6OP23”
5C07

INC (IX+FLAW)

Bump the value stored in the 60H sector of the GAT Table in RAM, which is the number of flawed tracks.

5C0A

JR NZ,L66O23
[5C10H]

If the NZ FLAG (Not Zero) is set, then the track is not flawed, so JUMP to 5C10H.

5C0C

LD (IX+00H),USDTRK

Store the value held in Register 3FH (i.e., the indicator that the GRAN is used) into the memory location IX+00H.

“L66O23”
5C10

LD A,(IX+00H)

Fetch the value stored at the memory location pointed to by IX+00H (i.e., the allocation status) and put it into Register A.

5C13

LD B,NGRAN

LET Register B = 06H, which is the number of grans in a block.

“L6OP22”
5C15

RRA

Rotate Register A’s bits right one bit position, with Bit 0 going to the CARRY FLAG, and the old CARRY FLAG, going to Bit 7. This will allow us to check the gran by simply working with the CARRY FLAG.

5C16

CCF

Invert the state of the CARRY FLAG.

5C17

ADC HL,DE

Add WITH CARRY Register Pair HL (i.e., a running total) and Register Pair DE.

5C19

DJNZ L6OP22
[5C15H]

LOOP back to 5C15H, reducing Register B each time, and continue to LOOP until Register B has been reduced to ZERO, in which case, continue with the next instruction.

5C1B

INC IX

INCrement the value stored in Register Pair IX (i.e., the pointer to the current track being examined in the GAT TABLE in RAM) by 1.

5C1D

DEC C

DECrement the value stored in Register C (i.e., the tracks left to be checked) by 1.

5C1E

JR NZ,L6OP23
[5C07H]

If the NZ FLAG (Not Zero) is set, meaning that Register C still shows we have tracks to scan, JUMP to 5C07H.

5C20

PUSH HL

Save Register Pair HL (i.e., the running total of the count) to the top of the stack.

5C21

LD HL,FIRST

LET Register Pair HL = 5CA3H, which is a pointer to the “* * *” message pointer.

5C24

CALL PRT2
[6147H]

GOSUB to 6147H to display/print the message being poted to by Register Pair HL (i.e., “* * *“).

5C27

POP HL

Put the value held at the top of the STACK (i.e., the running total of the count) into Restore Register Pair HL, and then remove the entry from the stack.

5C28

CALL BINDC1
[61CAH]

GOSUB to 61CAH (which is in the middle of the 61C1H routine to display the contents of Register Pair HL in decimal form).

5C2B

LD HL,5CA7H

LET Register Pair HL = 5CA7H, which is a pointer to the “FREE GRANULES” message pointer.

5C2E

CALL PRT2
[6147H]

GOSUB to 6147H to display/print the message being poted to by Register Pair HL (i.e., “* * *“).

5C31

RET

RETurn to the caller.

5C32H – MESSAGE AND STORAGE for the “DIR” Command.

“TITL2”
5C32

DEFM …

“DISK NAME: “.

“DSKN2”

DEFM …

“ DRIVE: “

“DRV2”

DEFM …

“ “

“DSIDE2”

DEFM …

“ “

“DATE2”

DEFM …

“ ” + 0DH

“TITL4”
5C65

DEFM …

“FILENAME ATTRB LRL #REC “.

5C89

DEFM …

“#GRN EEXT EOF DATE:” + 0DH.

“FIRST”
5CA3

DEFM …

“***” + 03H.

“SECND”
5CA7

DEFM …

“ FREE GRANULES ***” + 0DH.

DETA”
5CBA

DEFM …

“ “.

“MTH”

DEFM …

“00/“

“YER”

DEFM …

“00” + 0DH.

5CC3H – “DIR” Command Parameter Table.

“SWTCH3”
5CC3

DEFM ‘SYS ‘

DEFW SYS

DEFM ‘INV ‘

DEFW INV

“PRT”
5CD3

DEFM ‘PRT ‘

DEFW LPFLAG

DEFB 00H

5CDCH – “FREE” Library Command.

“S6FREE”
5CDC

LD BC,0000H

LET Register Pair BC = 0000H so that we can clear the PRINTER FLAG in the next instruction.

5CDF

LD (LPFLAG),BC

Store the value held in Register BC (i.e., 0000H) into the memory location 5A4DH (i.e., the byte flag for PRINT).

5CE3

LD A,(HL)

Fetch the first character stored at memory location pointed to by Register Pair HL (i.e., the pointer to the beginning of the command line which was passed to this Overlay on entry) and put it into Register A.

5CE4

CP 3AH

Prepare to test for a DRIVE NUMBER by comparing the value held in Register A against 3AH (ASCII: :). Results: If Register A equals :, the Z FLAG is set; otherwise the NZ FLAG is set.

5CE6

JR NZ,NODRV
[52FFH]

If we did not get a : the NZ FLAG (Not Zero) is set, so JUMP to 5CFDH.

5CE8

INC HL

Bump the value stored in Register Pair HL by 1 so as to point to the next character stored at memory location pointed to by Register Pair HL (i.e., the command line which was passed to this Overlay on entry). If we had a :, then this would be a drive number.

5CE9

LD A,(HL)

Fetch the value stored at memory location (i.e., the character following a “:” on the command line) pointed to by Register Pair HL and put it into Register A.

5CEA

INC HL

5CEB

SUB 30H

SUBtract the value 30H from Register A (i.e., the 2nd character on the command line if the first character was a “:”). Note: Subtracting 30H from from Register A will convert an ASCII number ‘0’-‘9’ to its decimal equivalent (i.e., 6 in ASCII is 36H in Hex; so 36H-30H = 6).

5CED

JP C,ERR9
[5234H]

If the C FLAG (Carry) is set then the character’s value was too low to be a number, so JUMP to 5234H.

5CF0

CP TOPDRV

Compare the value held in Register A against 04H, which is 1 + the maximum number of drives permitted on a TRSDOS v1.3 system. Results:

If Register A equals 04H, the Z FLAG is set.
If A < 1 + the maximum number drives permitted, the CARRY FLAG will be set.
if A >= 1 + the maximum number drives permitted, the NO CARRY FLAG will be set.

5CF2

JP NC,ERR9
[5234H]

If the NC FLAG (No Carry) is set then the character we are testing for a drive number was >= 1 + the maximum number drives permitted, meaning it was not a proper drive number, so JUMP to 5234H.

5CF5

LD C,A

LET Register C = Register A (i.e., the partially valided drive number from the command line).

5CF6

LD A,(MAXDRV)

Fetch the value stored at memory location 4413H and put it into Register A.
NOTE: 4413H is the storage location for the NUMBER OF DISK DRIVES in the system.

5CF9

CP C

Compare the value held in Register A (i.e., the number of disk drives actually present on the system) against the value held in Register C (i.e., the partially valided drive number from the command line). Results: If the number of disk drives actually present on the system (Register A) >= the partially valided drive number from the command line (Register C), then the drive number requested is present on the system, and the NC FLAG will be set; if the requested drivee is higher than the number of drives available, the CARRY FLAG will be set.

5CFA

JP C,ERR9
[5234H]

If the C FLAG (Carry) is set then the requested drive number is higher than the highest disk drive on the system so JUMP to 5234H.

“NODRV”
5CFD

LD A,C

LET Register A = Register C (i.e., the fully validated drive number specified on the command line).

5CFE

ADD A,30H

LET Register A = Register A + 30H. Note: Adding 30H to from Register A will convert decimal number 0-9 into its ASCII equivalent (i.e., 6 + 30H = 36H, which, in ASCII, is 6.

5D00

LD (DRIVE),A

Store the value held in Register A (i.e., the ASCII representation of the fully validated drive number specified on the command line) into the memory location 5E0DH, which is in the MESSAGE STORAGE AREA for the “FREE” Command.

5D03

PUSH BC

Save Register Pair BC (i.e., the fully validated drive number specified on the command line) to the top of the stack.

5D04

LD DE,SWTCH1

LET Register Pair DE = 5CD3H, which is the pointer to the “PRT ” message.

5D07

CALL SWITCH
[4454H]

GOSUB to 4454H.
NOTE: 4454H is the DOS PARAMETER STRING PARSE routine. It decodes DOS LIBRARY parameters.

5D0A

POP BC

Put the value held at the top of the STACK (i.e., the fully validated drive number specified on the command line) into Restore Register Pair BC, and then remove the entry from the stack.

5D0B

JP NZ,ERR2
[5214H]

If the NZ FLAG (Not Zero) is set, then the CALL for the DOS PARAMETER STRING PARSE returned an error, so JUMP to 5214H.

5D0E

CALL TRKGET
[4B3EH]

GOSUB to 4B3EH to prepare the diskette for a DIRECTORY READ.

5D11

LD A,D

LET Register A = Register D (i.e., the directory track number).

5D12

LD (CDIRET),A

Store the value held in Register A (i.e., the directory track number) into the memory location 5E45H (which is the DEFB storage area for the directory track number).

5D15

CALL RDGAT
[4A93H]

GOSUB to 4A93H.
NOTE: 4A93H is the SYS00/SYS routine to READ THE GAT sector into RAM (Buffer at 4D00H).

5D18

JP NZ,ERR
[6132H]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned because of an ERROR, JUMP to 6132H.

5D1B

LD HLBUFF2 + DID

LET Register Pair HL = 4DD0H, which is the pointer to the memory location holding the FILENAME in the GAT SECTOR we just read.

5D1E

LD DE,DSKNAM

LET Register Pair DE = 5DE7H, which is a pointer to the MESSAGE STORAGE AREA for the FREE commad.

5D21

LD BC,0008H

LET Register Pair BC = 0008H, which is the number of bytes in a filename (and therefore is the number of bytes to move).

5D24

LDIR

Copy the filename from the GAT SECTOR into the MESSAGE STORAGE AREA via LDIR, which transfers a byte of data from the memory location pointed to by HL to the memory location pointed to by DE. Then HL and DE are incremented and BC is decremented. If BC is not zero, this operation is repeated. Interrupts can trigger while this instruction is processing.

5D26

LD BC,(LPFLAG)

Fetch the value stored at memory location 5A4DH (i.e., the PRINTER OUTPUT flag) and put it into Register BC.

5D2B
5D2A

LD A,B
OR C

Since the Z-80 cannot test Register Pair BC against zero, the common trick is to set Register A to equal to Register B, and then OR A against Register C. Only if both Register B and Register C were zero can the Z FLAG be set.

5D2C

JR NZ,CONTD
[5D31H]

If the NZ FLAG (Not Zero) is set, then PRINTER OUTPUT is selected, so skip the display routine which is next and JUMP to 5D31H.

5D2E

CALL CLS
[01C9H]

GOSUB to 01C9H which is the Model III ROM Routine to Clear the Screen.

“CONTD”
5D31

LD B,15H

LET Register B = 15H (Decimal: 21) for the 21 spaces we are about to print.

5D33

LD A,20H

LET Register A = 20H (ASCII: SPACE) for the 21 spaces we are about to print.

“L6OP33”
5D35

CALL PDATA
[6135H]

GOSUB to 6135H to display or print the character held in Register A; routine affects Registers A and E.

5D38

DJNZ L6OP33
[5D35H]

LOOP back to 5D35H, reducing Register B each time, and continue to LOOP until Register B has been reduced to ZERO, in which case, continue with the next instruction.

5D3A

LD HL,TITLE

LET Register Pair HL = 5DC2H which is the MESSAGE STORAGE AREA for “ FREE SPACE MAP “.

5D3D

CALL PRT2
[6147H]

GOSUB to 6147H to either display or print the message pointed to by Register Pair HL.

5D40

LD HL,TITL3

LET Register Pair HL = 5DDDH which is the MESSAGE STORAGE AREA for “?????“.

5D43

CALL PRT2
[6147H]

GOSUB to 6147H to either display or print the message pointed to by Register Pair HL.

5D46

LD A,0FFH

LET Register A = 0FFH to prepare for initializing the track number.

5D48

LD (COUNT),A

Store the value held in Register A into the memory location 5E44H (i.e., the byte storage area set up to hold the track number) so that it can be fetched within the below loop.

5D4B

LD HL,BUFF2

LET Register Pair HL = 4D00H, which is the BUFFER into which the GAT TABLE has been read.

“L6OP7”
5D4E

LD A,(COUNT)

Fetch the value stored at memory location 5E44H (i.e., the byte storage area set up to hold the track number) and put it into Register A.

5D51

INC A

INCrement the value stored in Register A (i.e., the track number) by 1.

5D52

CP MAXTRK

Compare the value held in Register A against 28H (Decimal: 40), which is the maximum number of tracks on a disk. Results: If Register A (i.e., the track number) >= 40, the NO CARRY FLAG will be set.

5D54

RET NC

If the NC FLAG (No Carry) is set then we are at (or beyond) the end of the disk, so RETurn to the caller.

5D55

PUSH HL

Save Register Pair HL (i.e., the pointer to the GAT sector in RAM) to the top of the stack.

5D56

PUSH AF

Save Register Pair AF (i.e., the track number) to the top of the stack.

5D57

LD HL,LOW

LET Register Pair HL = 5E0FH, which is the MESSAGE STORAGE AREA for “nn-nn: XXXXXXX : XXXXXX : XXXXXX : XXXXXX : XXXXXX“.

5D5A

CALL HEXCOV
[5E46H]

GOSUB to 5E46H to put the first track number in the data line for printout.

5D5D

POP AF

Put the value held at the top of the STACK into Restore Register Pair AF (i.e., the track number), and then remove the entry from the stack.

5D5E

ADD A,04H

LET Register A = Register A (i.e., the track number) + 04H.

5D60

LD (COUNT),A

Store the value held in Register A (i.e., the track number + 4) into the memory location 5E44H (i.e., the byte storage area set up to hold the track number).

5D63

LD HL,LOW + 3

LET Register Pair HL = 5E12H which is the pointer for the fourth track number in the data line for prinout.

5D66

CALL HEXCOV
[5E46H]

GOSUB to 5E46H to put the fourth track number in the data line for printout.

5D69

LD DE,TABLE

LET Register Pair DE = 5E19H which is the pointer to the start of track data.

5D6C

POP HL

Put the value held at the top of the STACK (i.e., the pointer to the GAT table in RAM) into Restore Register Pair HL, and then remove the entry from the stack.

5D6D

LD B,05H

LET Register B = 05H for a loop of 5 tracks.

“L6OO8”
5D6F

PUSH HL

Save Register Pair HL (i.e., the pointer to the GAT table in RAM) to the top of the stack.

5D70

PUSH DE

Save Register Pair DE to the top of the stack.

5D71

LD DE,FLAW

LET Register Pair DE = 0060H which will be an offset to HL so that HL will point to the track existence table in the GAT sector.

5D74

ADD HL,DE

LET Register Pair HL = Register Pair HL + Register DE.

5D75

LD A,(HL)

Fetch the value stored at memory location pointed to by Register Pair HL (i.e., the the track existence table in the GAT sector) and put it into Register A.

5D76

POP DE

Put the value held at the top of the STACK into Restore Register Pair DE, and then remove the entry from the stack.

5D77

POP HL

Put the value held at the top of the STACK (i.e., the pointer to the GAT table in RAM) into Restore Register Pair HL, and then remove the entry from the stack.

5D78

CP 0FFH

Compare the value held in Register A against 0FFH to test for a flawed track. Results: If Register A equals 0FFH, the Z FLAG is set; otherwise the NZ FLAG is set.

5D7A

JR NZ,L6PO9
[5D8EH]

If the NZ FLAG (Not Zero) is set then the track is NOT flawed so skip the flawed track display routine and JUMP to 5D8EH.

“L66P08”
5D7C

LD IX,GFLAW

LET Register Pair IX = 5DD1H so as to point to “FLAWED”.

“L6PO8”
5D80

PUSH BC

Save Register Pair BC (i.e., the count) to the top of the stack.

5D81

LD B,NGRAN

LET Register B = 06H for a DJNZ loop of 6 iterations (i.e., the number of grans on a track) to move bytes from IX to DE.

“L6OOP8”
5D83

LD A,(IX+00H)

Fetch the value stored at the memory location pointed to by IX+00H and put it into Register A.

5D86

LD (DE),A

Store the value held in Register A into the memory location pointed to by Register Pair DE.

5D87

INC IX

INCrement the value stored in Register Pair IX by 1.

5D89

INC DE

INCrement the value stored in Register Pair DE by 1.

5D8A

DJNZ L6OO8
[5D83H]

LOOP back to 5D83H, reducing Register B each time, and continue to LOOP until Register B has been reduced to ZERO, in which case, continue with the next instruction.

5D8C

JR L6PO20
[5DACH]

JUMP to 5DACH.

5D8EH – Continuation of the “FREE” command. Jumped here if the track is NOT flawed (so as to skip the display of a flawed track).

“L6PO9”
5D8E

LD A,(CDIRET)

Fetch the value stored at memory location 5E45H (i.e., the directory track number) and put it into Register A.

5D91

CP L

Compare the value held in Register A against the value held in Register L. Results: If Register A equals Register L, the Z FLAG is set; otherwise the NZ FLAG is set.

5D92

JR NZ,L6PO10
[5D9AH]

If the NZ FLAG (Not Zero) is set then we have not yet reached the directory track, so JUMP to 5D9AH.

5D94

LD IX,GDIR

If we are here, we have finally hit the directory sector. LET Register Pair IX = 5DD7H to point to “DIRECT”.

5D98

JR L6PO8
[5D80H]

JUMP to 5D80H.

5D9AH – Continuation of the “FREE” command. Jumped here if the track is NOT flawed (so as to skip the display of a flawed track) and we have not yet hit the directory track.

“L6PO10”
5D9A

LD C,(HL)

Fetch the value stored at memory location (i.e., the allocation bytes) pointed to by Register Pair HL and put it into Register C.

“L60010”
5D9B

PUSH BC

Save Register Pair BC (i.e., the count) to the top of the stack.

5D9C

LD B,NGRAN

LET Register B = 06H for a DJNZ loop of 6 iterations to move bytes from IX to DE.

“L6PO11”
5D9E

SRL C

We need to see if the gran at issue is allocated so a SRL C is involked whereby the contents of Register C are shifted right one bit position, with bit 0 copied to the carry flag and a zero put into bit 7.

5DA0

JR C,SETX
[5DA6H]

If the C FLAG (Carry) is set (meaning bit 0 of Register C was set), then the gran was allocated, so JUMP to 5DA6H.

5DA2

LD A,2EH

LET Register A = 2EH (ASCII: .).

5DA4

JR SETXX
[5DA8H]

JUMP to 5DA8H.

5DA6H – Continuation of the “FREE” command. Jumped here if the track is NOT flawed (so as to skip the display of a flawed track) and we have not yet hit the directory track AND the gran is allocated.

“SETX”
5DA6

LD A,58H

LET Register A = 58H (ASCII: X).

“SETXX”
5DA8

LD (DE),A

Store the value held in Register A into the memory location pointed to by Register Pair DE (i.e., a location in the data line to be output).

5DA9

INC DE

INCrement the value stored in Register Pair DE (i.e., a location in the data line to be output) by 1.

5DAA

DJNZ L6PO11
[5D9EH]

LOOP back to 5D9EH, reducing Register B each time, and continue to LOOP until Register B has been reduced to ZERO, in which case, continue with the next instruction.

“L6PO20”
5DAC

POP BC

Put the value held at the top of the STACK (i.e., the counter) into Restore Register Pair BC, and then remove the entry from the stack.

5DAD

PUSH HL

Save Register Pair HL (i.e., a pointer in the GAT SECTOR in RAM) to the top of the stack.

5DAE

LD HL,0003H

LET Register Pair HL = 0003H to prepare to skip over 3 spaces in the data line to be output.

5DB1

ADD HL,DE

LET Register Pair HL = Register Pair HL (i.e. 3) + Register DE (the pointer to the the data line to be output).

5DB2

EX DE,HL

EXchange the value stored in Register Pair HL (the pointer to the the data line to be output + 3) with the value stored in Register Pair DE (the pointer to the the data line to be output).

5DB3

POP HL

Put the value held at the top of the STACK (i.e., a pointer in the GAT SECTOR in RAM) into Restore Register Pair HL, and then remove the entry from the stack.

5DB4

INC HL

INCrement the value stored in Register Pair HL (i.e., a pointer in the GAT SECTOR in RAM) by 1.

5DB5

DJNZ L6OO8
[5D6FH]

LOOP back to 5D6FH (to loop over tracks), reducing Register B each time, and continue to LOOP until Register B has been reduced to ZERO, in which case, continue with the next instruction.

5DB7

PUSH HL

Save Register Pair HL (i.e., a pointer in the GAT SECTOR in RAM) to the top of the stack.

5DB8

LD HL,LOW

LET Register Pair HL = 5E0FH to point to the data line.

5DBB

CALL PRT2
[6147H]

GOSUB to 6147H to either display or print the message pointed to by Register Pair HL.

5DBE

POP HL

Put the value held at the top of the STACK into Restore Register Pair HL, and then remove the entry from the stack.

5DBF

JP L6OP7
[5D4EH]

JUMP to 5D4EH to keep looping over the entire disk.

5DC2H – MESSAGE and BYTE STORAGE AREA for “FREE”.

“TITLE”
5DC2

DEFM ‘FREE SPACE MAP” + 0DH

“GFLAW”
5DD1

DEFM ‘FLAWED’

“GDIR”
5DD7

DEFM ‘DIRECT’

“TITL3”
5DDD

DEFM ‘TRK # ‘

“DSKNAM”

DEFM ‘SIDE: —————— DRIVE: ‘

“DRIVE”

DEFM ‘ ‘ + 0DH

“LOW”
5E0F

DEFM ‘ – : ‘

“TABLE”

DEFM …

“‘ : : : : ‘ + 0DH“.

“COUNT”
5E44

DEFB 0

Storage area for the Track Number.

“CDIRET”
5E45

DEFB 0

Storage area for the Directory’s Track Number.

5E46H – Subroutine in the “FREE” Library Command to Generate a 2-Digit Decimal Number.

“HEXCOV”
5E46

LD (HL),2FH

Store the value of 1 character below “0” into the memory location pointed to by Register Pair HL.

“HEXCO2”
5E48

INC (HL)

Increase the character held in Register Pair HL by 1.

5E49

SUB 0AH

SUBtract 10 from that character value.

5E4B

JR NC,HEXCO2
[5E48H]

If the NC FLAG (No Carry) is set, the value went negative, so JUMP to 5E48H.

“HEXCO1”
5E4D

ADD A,3AH

LET Register A = Register A (i.e., the remainder from that subtraction) + 3AH to convert that value to ASCII.

5E4F

INC HL

INCrement the value stored in Register Pair HL by 1 to point to the byte which will hold the second digit.

5E50

LD (HL),A

Store the value held in Register A (i.e., the remainder from that subtraction + 3AH) into the memory location pointed to by Register Pair HL.

5E51

RET

RETurn to the caller.

5E52H – “CREATE” Library Command.

“CREATE”
5E52

LD BC,0000H

LET Register Pair BC = 0000H.

5E55

LD (NRECS),BC

Store the value held in Register BC (i.e., 0000H) into the memory location 5E95H (i.e., the storage location for the NUMBER OF RECORDS).

5E59

LD (S6LRL),BC

Store the value held in Register BC (i.e., 0000H) into the memory location 5E7FH (i.e., the storage location for the LOGICAL RECORD LENGTH).

5E5D

CALL GETSYN
[623AH]

GOSUB to 623AH to isolate and validate the FILESPEC from the command line via an OVERLAY call to ROUTINE 4 of OVERLAY 1.

5E60

JP NZ,ERR3
[5218H]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned because of an ERROR, JUMP to 5218H.

“CONT10”
5E63

LD DESWTCH2

LET Register Pair DE = 5EB1H to point to the valid parameter table (which is either REC or LRL).

5E66

CALL SWITCH
[4454H]

GOSUB to 4454H.
NOTE: 4454H is the DOS PARAMETER STRING PARSE routine. It decodes DOS LIBRARY parameters.

5E69

JP NZ,ERR2
[5214H]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned because of an ERROR, JUMP to 5214H.

5E6C

LD HL,(NRECS)

Fetch the value stored at memory location 5E95H (i.e., the storage location for the number of records) and put it into Register HL.

5E6F

CALL CONVHX
[5EC2H]

GOSUB to 5EC2H to convert the Binary Coded Decimal Value Pointed to by Register Pair HL into Binary.

5E72

LD (NRECS),HL

Store the value held in Register HL (i.e., the converted value) into the memory location 5E95H (i.e., the storage location for the number of records).

5E75

LD HL,(S6LRL)

Fetch the value stored at memory location 5E7FH (i.e., the storage location for the LRL) and put it into Register HL.

5E78

CALL CONVHX
[5EC2H]

GOSUB to 5EC2H to convert the Binary Coded Decimal Value Pointed to by Register Pair HL into Binary.

5E7B

LD (S6LRL),HL

Store the value held in Register HL into the memory location 5E7FH (i.e., the storage location for the LRL).

5E7E

LD BC,S6LRL

LET Register Pair BC = the value stored in the memory locations 5E7F-5E80H, which represet the LRL, and which were placed here by other instructions in this overlay.

5E81

LD A,B

LET Register A = Register B (i.e., the MSB of the LRL).

5E82

CP 02H

Compare the value held in Register A (i.e., the MSB of the LRL) against 02H. Result: if A >= 02H, the NO CARRY FLAG will be set.

5E84

JP NC,ERR2
[5214H]

If the NC FLAG (No Carry) is set then the LRL is too big, so JUMP to 5214H.

5E87

LD B,C

LET Register B = Register C (i.e., the LSB of the LRL).

5E88

CALL GETDC1
[622DH]

GOSUB to 622DH to set the parameters for an OVERLAY call to open a file.

5E8B

CALL INIT
[4420H]

5E8E

JP NZ,ERR
[6132H]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned because of an ERROR, JUMP to 6132H.

5E91

JP NC,ERR1
[521CH]

If the NC FLAG (No Carry) is set then that CALL resulted in a “FILE ALREADY EXISTS” status, so JUMP to 521CH.

5E94

LD BC,NRECS

LET Register Pair BC = the value stored in the memory locations 5E95H-5E96H, which represet the NUMBER OF RECORDS, and which were placed here by other instructions in this overlay.

“L6OP12”
5E97
5E98

LD A,B
OR C

5E99

JP Z,CLOZE1
[56F6H]

If the number of records is zero (or not supplied), then the Z FLAG (Zero) is set, so JUMP to 56F6H to close and exit.

5E9C

DEC BC

If we are here, then we were given a NUMBER OF RECORDS in excess of ZERO. DECrement the value stored in Register Pair BC (i.e., the record number to position to) by 1.

5E9D

LD DE,S6DCB1

LET Register Pair DE = 6280H, which will be the DCB address.

5EA0

PUSH DE

Save Register Pair DE (i.e., the DCB address) to the top of the stack.

5EA1

CALL POSN
[4442H]

GOSUB to 4442H to position the file to the last record.

5EA4

POP DE

Put the value held at the top of the STACK (i.e., the DCB address) into Restore Register Pair DE, and then remove the entry from the stack.

5EA5

LD HL,3C00H

LET Register Pair HL = 3C00H, which is the first character location on the screen.

5EA8

CALL WRITE
[4439H]

GOSUB to 4439H to write from the video screen to a file.

5EAB

JP NZ,ERR
[6132H]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned because of an ERROR, JUMP to 6132H.

5EAE

JP CLOZE1
[56F6H]

JUMP to 56F6H to close the file and exit.

5EB1H – PARAMETER TABLE for the “CREATE” Command.

“SWTCH2”
5EB1

DEFM …

“REC “.

5E91

DEFM …

“LRL “.

DEFW S6LRL

5EC1

DEFB 00H

End of Table Delimeter.

5EC2H – SUBROUTINE in the “CREATE” Command to Convert the Binary Coded Decimal Value Pointed to by Register Pair HL into Binary.

“CONVHX”
5EC2

LD IX,0000H

LET Register Pair IX = 0000H, which is where the results will be stored.

5EC6

LD IY,POWR10

LET Register Pair IY = 5EF7H, which is a pointer to a POWER OF TEN table.

5ECA

LD A,H

LET Register A = Register H (i.e., the MSB).

5ECB

CALL ADDHL
[5ED6H]

GOSUB to 5ED6H to convert from Hexadecimal.

5ECE

LD A,L

LET Register A = Register L (i.e., the LSB).

5ECF

CALL ADDHL
[5ED6H]

GOSUB to 5ED6H to convert from Hexadecimal.

5ED4
5ED2

PUSH IX
POP HL

Let Register Pair HL = Register Pair IX.

5ED5

RET

RETurn to the caller.

5ED6H – SUBROUTINE to the above SUBROUTINE in the “CREATE” Command. Converts the value held in A to Hexadecimal.

“ADDHL”
5ED6

PUSH AF

Save Register Pair AF (i.e., the byte we are converting) to the top of the stack.

5ED9
5ED7
5EDB
5EDD

SRA A
SRA A
SRA A
SRA A

Shift the contents of Register A right one bit position four times. In each iteration, the contents of bit 0 are copied to the carry flag and the previous contents of bit 7 are unchanged. This basically erases the low nybble.

5EDF

CALL ADDIX
[5EE3H]

GOSUB to 5EE3H to convert Register A to a Decimal Decoded number.

5EE2

POP AF

Put the value held at the top of the STACK into Restore Register Pair AF (i.e., the byte we are converting), and then remove the entry from the stack.

“ADDIX”
5EE3

AND 0FH

MASK the value of Register A against 0FH (0000 1111) to keep only bits 3, 2, 1, 0, which turns Register A into the low nybble of Register A.

5EE5

LD B,A

LET Register B = Register A (i.e., the low nybble of the byte we are converting).

The next few instructions get the appropriate power of 10 from a table.

5EE6

LD E,(IY+00H)

Fetch the value stored at memory location IY+00H and put it into Register E.

5EE9

INC IY

INCrement the value stored in Register Pair IY by 1.

5EEB

LD D,(IY+00H)

Fetch the value stored at memory location IY+00H and put it into Register D.

5EEE

INC IY

INCrement the value stored in Register Pair IY by 1.

5EF0

INC B

INCrement the value stored in Register B by 1.

“ADDIX1”
5EF1

DEC B

DECrement the value stored in Register B by 1 so as to trigger a Z or NZ flag.

5EF2

RET Z

If the Z FLAG (Zero) is set, then our digit is zero, so RETurn to the caller.

5EF3

ADD IX,DE

LET Register Pair IX = Register Pair IX (i.e., returning code) + Register DE (i.e., the table value).

5EF5

JR ADDIX1
[5EF1H]

LOOP BACK 3 instructions to 5EF1H.

5EF7H – POWERS OF 10 TABLE for the “CREATE” Command.

“POWR10”
5EF7

E8 03

This is hex for 1000.

5EF9

64 00

This is hex for 100.

5EFB

This is hex for 10.

5EFC

This is hex for 0.

5EFFH – “CLEAR” Library Command.

“CLEAR”
5EFF

LD BC,0000H

LET Register Pair BC = 0000H so we can zero out the following memory locations.

5F02

LD (LOWRAM),BC

Store the value held in Register BC (i.e., 0000H) into the memory location 5F29H (i.e., the memory location storing the STARTING ADDRESS).

5F06

LD (HIGHRAM),BC

Store the value held in Register BC (i.e., 0000H) into the memory location 5F38H (i.e., the memory location storing the ENDING ADDRESS).

5F0A

LD (NEWMEM),BC

Store the value held in Register BC (i.e., 0000H) into the memory location 5F4CH (i.e., the memory location storing the MEMORY PROTECT ADDRESS).

5F0E

LD A,(HL)

Fetch the value stored at memory location pointed to by Register Pair HL (i.e., the pointer to the command line entered by the USER after the library command itself) and put it into Register A.

5F0F

CP 0DH

Compare the value held in Register A against 0DH (ASCII: CARRIAGE RETURN). Results: If Register A equals CARRIAGE RETURN, the Z FLAG is set; otherwise the NZ FLAG is set.

5F11

JR NZ,CLEARX
[5F1FH]

If the NZ FLAG (Not Zero) is set, then we have parameters (i.e., we didn’t just get a CARRIAGE RETURN) so JUMP to 5F1FH.

5F13

LD A,(DOFLAG)

Fetch the value stored at memory location 4CFDH (i.e., the memory location storing whether the DO command is active or not) and put it into Register A.

5F16

OR A

Since a LD command does not set any FLAGS, Set FLAGS based on the contents of Register A.

5F17

JR Z,CLEAR0
[5F63H]

If the Z FLAG (Zero) is set, then the DO command is NOT active, so JUMP to 5F63H.

5F19

LD HL,CNTCLR

LET Register Pair HL = 5FAAH which is a pointer to an error message, since you are not permitted to CLEAR memory while DO is active.

5F1C

JP PRINT
[021BH]

JUMP to 021BH.
NOTE: 021BH will display the character at (HL) until a 03H is found.

5F1FH – Subroutine in the “CLEAR” Library Command. Jumped to if we have parameters on the command line.

“CLEARX”
5F1F

LD DE,CLRTAB

LET Register Pair DE = 5F91H to point to the PARAMETER TABLE for the CLEAR command.

5F22

CALL SWITCH
[4454H]

GOSUB to 4454H.
NOTE: 4454H is the DOS PARAMETER STRING PARSE routine. It decodes DOS LIBRARY parameters.

5F25

JP NZ,ERR2
[5214H]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned because of an ERROR, JUMP to 5214H.

5F28

LD DE,LOWRAM

LET Register Pair DE = the value stored in 5F29H-5F30H (i.e., the memory location storing the STARTING ADDRESS), which was placed here by other instructions in this overlay.

5F2B
5F2C

LD A,D
OR E

5F2D

JR Z,CHKMEM
[5F4BH]

If the Z FLAG (Zero) is set, then the START entry was ZERO, so JUMP to 5F4BH.

5F2F

LD HL,6000H

LET Register Pair HL = 6000H, which is the lowest RAM location which is permitted.

5F32

SBC HL,DE

Subtracts the value stored in Register Pair DE (i.e., the memory location storing the STARTING ADDRESS) and the carry flag from the value stored in Register Pair HL (i.e., 6000H, the floor of the permitted STARTING address).

5F34

JP NC,ERR6
[5225H]

If the NC FLAG (No Carry) is set, then that subtraction didn’t trigger an overflow, so we were given a STARTING ADDRESS which is too low. JUMP to 5225H.

5F37

LD HL,HIGHRAM

LET Register Pair DE = the value stored in 5F29H-5F30H (i.e., the memory location storing the ENDING ADDRESS), which was placed here by other instructions in this overlay.

5F3A

SBC HL,DE

Subtracts the value stored in Register Pair DE (i.e., the memory location storing the ENDING ADDRESS) and the carry flag from the value stored in Register Pair HL (i.e., the STARTING ADDRESS).

5F3C

JP C,ERR5
[5220H]

If the C FLAG (Carry) is set then that subtraction triggered an overflow, so JUMP to 5220H to exit.

5F3F

JP Z,ERR5
[5220H]

If the Z FLAG (Zero) is set then the START and END addresses are the same, so JUMP to 5220H to exit.

5F42
5F43

LD B,H
LD C,L

Let Register Pair BC = Register Pair HL (i.e., the ENDING ADDRESS – STARTING ADDRESS).

5F44
5F45

LD H,D
LD L,E

LET Register Pair HL = Register Pair DE (i.e., the STARTING ADDRESS).

5F46

INC DE

INCrement the value stored in Register Pair DE (i.e., the STARTING ADDRESS) by 1.

5F47

LD (HL),00H

Store a 00H into the memory location pointed to by Register Pair HL.

5F49

LDIR

Clear the entire area by using a LDIR command, which transfers a byte of data from the memory location pointed to by HL to the memory location pointed to by DE. Then HL and DE are incremented and BC is decremented. If BC is not zero, this operation is repeated. Interrupts can trigger while this instruction is processing.

“CHKMEM”
5F4B

LD HL,NEWMEM

LET Register Pair HL = the value stored in 5F4CH-5F4DH (i.e., the memory location storing the MEMORY PROTECT ADDRESS), which was placed here by other instructions in this overlay.

5F4E
5F4F

LD A,H
OR L

5F50

JP Z,CLS
[01C9H]

If the Z FLAG (Zero) is set, then there was either NO memory protect address given or it was zero, so JUMP to 01C9H which is the Model III ROM Routine to clear the screen (and this routine will exit after that).

5F53

EX DE,HL

EXchange the value stored in Register Pair HL (i.e., the memory location storing the MEMORY PROTECT ADDRESS) with the value stored in Register Pair DE. Register Pair DE will now contain the the memory location storing the MEMORY PROTECT ADDRESS.

5F54

LD HL,5FFFH

LET Register Pair HL = 5FFFH (i.e., 1 byte lower than the lowest byte we will permit).

5F57

SBC HL,DE

Subtracts the value stored in Register Pair DE and the carry flag from the value stored in Register Pair HL.

5F59

JP NC,ERR6
[5225H]

If the NC FLAG (No Carry) is set that means the User tried to set the MEMORY PROTECT ADDRESS to less than 6000H, which is invalid, so JUMP to 5225H.

5F5C

LD (MEMEND),DE

Store the value held in Register DE into the memory location 4411H.
NOTE: 4411H is the storage location for the MEMORY PROTECT address.

5F60

JP CLS
[01C9H]

JUMP to 01C9H which is the Model III ROM Routine to clear the screen (and this routine will exit after that).

5F63H – Part of the “CREATE” Library Command. Jumped here if the user didn’t provide any parameters.

“CLEAR0”
5F63

LD DE,(MEM2)

Fetch the value stored at memory location 4415H and put it into Register DE.
NOTE: 4415H is the storage location for the ADDRESS OF THE END OF PHYSICAL MEMORY.

5F67

LD (MEMEND),DE

Store the value held in Register DE into the memory location 4411H.
NOTE: 4411H is the storage location for the MEMORY PROTECT address.

5F6B

LD HL,S6DCB1

LET Register Pair HL = 6280H, which will be the base memory address for a memory test.

5F6E

XOR A

Set Register A to ZERO and clear all Flags.

“L6OP9”
5F6F

LD (HL),A

Store the value held in Register A (i.e., a 00H) into the memory location pointed to by Register Pair HL.

5F70

CP (HL)

Compare the value held in Register A against the value held in the memory location (HL) to see if that LD command worked. Results: If Register A equals 00H, the Z FLAG is set; otherwise the NZ FLAG is set.

5F71

JR NZ,CLER1
[5F7BH]

If the NZ FLAG (Not Zero) is set then the LD command didn’t stick and we have a memory error, so JUMP to 5F7BH.

5F73

INC HL

INCrement the value stored in Register Pair HL (i.e., a location in RAM we are testing) by 1.

5F74

PUSH HL

Save Register Pair HL (i.e., a location in RAM we are testing) to the top of the stack.

5F75

OR A

Clear the CARRY flag, leave everything else alone.

5F76

SBC HL,DE

Subtracts the value stored in Register Pair DE (i.e., the END OF MEMORY) and the carry flag from the value stored in Register Pair HL (i.e., a location in RAM we are testing).

5F78

POP HL

Put the value held at the top of the STACK (i.e., a location in RAM we are testing) into Restore Register Pair HL, and then remove the entry from the stack.

5F79

JR NZ,L6OP9
[5F6FH]

If the NZ FLAG (Not Zero) is set, then we have not yet reached the end of MEMORY, so LOOP BACK to to 5F6FH to keep testing.

“CLER1”
5F7B

PUSH HL

Save Register Pair HL (i.e., the last location in RAM we are testing) to the top of the stack.

5F7C

OR A

Clear the CARRY flag, leave everything else alone.

5F7D

SBC HL,DE

Subtracts the value stored in Register Pair DE (i.e., the END OF MEMORY) and the carry flag from the value stored in Register Pair HL (i.e., the last location in RAM we are testing).

5F7F

POP DE

Put the value held at the top of the STACK (i.e., the last location in RAM we are testing) into Restore Register Pair DE, and then remove the entry from the stack.

5F80

JP NC,CLS
[01C9H]

If the NC FLAG (No Carry) is set then we are done testing, so JUMP to 01C9Hwhich is the Model III ROM Routine to clear the screen (and this routine will exit after that).

5F83

LD HL,HEXADD

LET Register Pair HL = 527BH, which is a pointer to a MESSAGE STORAGE AREA.

5F86

LD A,D

LET Register A = Register D (i.e., the MSB of the byte of RAM which failed).

5F87

CALL HEXS
[61A1H]

GOSUB to 61A1H to insert that value into the MESSAGE.

5F8A

LD A,E

LET Register A = Register E (i.e., the LSB of the byte of RAM which failed).

5F8B

CALL HEXS
[61A1H]

GOSUB to 61A1H to insert that value into the MESSAGE.

5F8E

JP ERR7
[522AH]

JUMP to 522AH to display the error and exit.

5F91H – PARAMETER TABLE for the “CLEAR” Command.

“CLRTAB”
5F91H

DEFM …

“START “.

5F99H

DEFM …

“END “.

5FA1H

DEFM …

“MEM “.

5FA9H

DEFB 00H

End of Table Delimeter.

5FAAH

DEFM …

“CAN’T CLEAR WHILE DO IS ACTIVE” + 0DH.

5FC9H – “BUILD” Library Command..

“BUILD”
5FC9

CALL GETSYN
[623AH]

GOSUB to 623AH to isolate and validate the FILESPEC from the command line via an OVERLAY call to ROUTINE 4 of OVERLAY 1.

5FCC

JP NZ,ERR3
[5218H]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned because of an ERROR, JUMP to 5218H.

5FCF

LD HL,EXT5

LET Register Pair HL = 60CCH to point to a default file extension.

5FD2

CALL PUTEXT
[444BH]

GOSUB to 444BH to add the extension pointed to by Register Pair HL to the end of the filename pointed to by Register Pair DE.

5FD5

CALL INITIT
[6234H]

GOSUB to 6234H to create a file.

5FD8

JP NZ,ERR
[6132H]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned because of an ERROR, JUMP to 6132H.

5FDB

LD HL,BRKPMT

LET Register Pair HL = 602BH to point to the MESSAGE “HIT BREAK TO EXIT“.

5FDE

CALL PRINT
[021BH]

GOSUB to 021BH.
NOTE: 021BH will display the character at (HL) until a 03H is found.

“BUILD1”
5FE1

LD HL,S6PRMP

LET Register Pair HL = 600FH to point to the MESSAGE “TYPE UP TO 63 CHARACTERS“.

5FE4

CALL PRINT
[021BH]

GOSUB to 021BH.
NOTE: 021BH will display the character at (HL) until a 03H is found.

5FE7

LD B,3FH

LET Register B = 3FH (Decimal: 63) which is the maximum number of characters permitted.

5FE9

LD HL,S6BUF2

LET Register Pair HL = 6400H, which will act as a buffer for the 63 characters being typed in.

5FEC

CALL KEYN
[0040H]

5FEF

JR C,BLDEXT
[6001H]

If the C FLAG (Carry) is set then the BREAK key was hit, so JUMP to 6001H.

5FF1

INC B

INCrement the value stored in Register B (i.e., the number of characters actually typed in) by 1.

5FF2

LD HLS6BUF2

LET Register Pair HL = 6400H, which will act as a buffer for the 63 characters being typed in.

“BUILD2”
5FF5

LD A,(HL)

Fetch the value stored at memory location (i.e., one of the characters which was just typed in) pointed to by Register Pair HL (i.e., a pointer to the buffer of characters typed in by the user) and put it into Register A.

5FF6

LD DE,S6DCB1

LET Register Pair DE = 6280H, which is the DCB address (which is needed for a call to 001BH).

5FF9

CALL PUT
[001BH]

GOSUB to 001BH.
NOTE: 001BH is the Model III ROM routine to output a byte (held in Register A) to a device. Register Pair DE has the DCB of the device to be output to. Z is set if the device is ready.
NOTE: 001BH is the Model III ROM routine to write a byte to an output device. Requires Register A to contain the byte to output and Register Pair DE to be the starting address of DCB of device. On exit, Z set if device ready. Uses AF.

5FFC

INC HL

INCrement the value stored in Register Pair HL (i.e., a pointer to the buffer of characters typed in by the user) by 1.

5FFD

DJNZ BUILD2
[5FF5H]

LOOP back to 5FF5H, reducing Register B each time, and continue to LOOP until Register B has been reduced to ZERO, in which case, continue with the next instruction.

5FFF

JR BUILD1
[5FE1H]

JUMP to 5FE1H to prompt for another line.

6001H – Contination of the “BUILD” Library Command; jumped to if a BREAK key was hit..

“BLDEXT”
6001

LD A,0FFH

LET Register A = 0FFH, which is an End of File designator.

6003

LD DE,S6DCB1

LET Register Pair DE = 6280H, which is the DCB address (which is needed for a call to 001BH).

6006

CALL PUT
[001BH]

6009

JP NZ,ERROR
[4409H]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned because of an ERROR, JUMP to 4409H.
NOTE: 4409H is the SYS00/SYS routine to process DOS errors.

600C

JP CLOZE1
[56F6H]

JUMP to 56F6H to close the file and exit.

600FH – MESSAGE and BYTE STORAGE AREA for “BUILD”.

“BRKPMT”
600F

DEFM …

“HIT BREAK TO EXIT” + 0DH.

“S6PRMP”
602B

DEFM …

“TYPE UP TO 63 CHARACTERS” + 0DH.

603DH – “DO” Library Command.

This command modifies the keyboard DCB to force the characters otherwise expected to be input to come from the DO FILE rather than the keyboard. The routine will supply 1 character each time itis called, just like someone typing each letter. The procedure is:

Get the end of memory address and reserve 544 bytes for use by the DO routine.
Relocate the DO routine to the top 256 bytes of that space. This is what the keyboard will call.
Set up the next lower 256 bytes as the file buffer for the DO.
Set up the next lower 32 bntes as the DCB for the DO file.

“DO”
603D

LD A,(DOFLAG)

Fetch the value stored at memory location 4CFDH (i.e., the memory location storing whether the DO command is active or not) and put it into Register A.

6040

OR A

Since a LD command does not set any FLAGS, Set FLAGS based on the contents of Register A.

6041

JP NZ,ERR2
[5214H]

If the NZ FLAG (Not Zero) is set, then the DO command is already active, so JUMP to 5214H to exit.

6044

DEC A

DECrement the value stored in Register A (i.e., the memory location which stores the flag for whether a DO command is active, which is definitely holding a 1), by 1 (i.e., to zero).

6045

LD (DOFLAG),A

Store the value held in Register A (i.e., 00H) into the memory location 4CFDH (i.e., the memory location which stores the flag for whether a DO command is active), to indicate that DO is active.

6048

PUSH HL

Save Register Pair HL (i.e., the pointer to the command line entered by the USER after the library command itself) to the top of the stack.

6049

LD HL,(MEM2)

Fetch the value stored at memory location 4415H and put it into Register HL.
NOTE: 4415H is the storage location for the ADDRESS OF THE END OF PHYSICAL MEMORY.

604C

LD (MEMEND),HL

Store the value held in Register HL into the memory location 4411H.
NOTE: 4411H is the storage location for the MEMORY PROTECT address.

604F

LD HL,(KDCB + 1)

Fetch the value stored at memory location 4016H (i.e., the keyboard driver address) and put it into Register HL.

6052

LD (GOSAVE),HL

Store the value held in Register HL into the memory location 42B1H.

6055

LD HL,(MEMEND)

Fetch the value stored at memory location 4411H and put it into Register HL.
NOTE: 4411H is the storage location for the MEMORY PROTECT address.

6058

LD L,90H

LET Register L = 90H (Decimal: 144) so as to back up 144 bytes.

605A

LD (KDCB + 1),HL

Store the value held in Register HL (i.e., the MEMORY PROTECT address) into the memory location 4016H (i.e., the keyboard driver address).

605D

PUSH HL

Save Register Pair HL (i.e., the keyboard driver address) to the top of the stack.

605E

LD DE,GOGO4 – GOGO1 + 5

LET Register Pair DE = 002BH (Decimal: 43) as a 43 byte offset to the DCB.

6061

ADD HL,DE

LET Register Pair HL = Register Pair HL (i.e., the keyboard driver address) + Register DE (i.e., a 43 byte offset).

6062

LD (GODCB),HL

Store the value held in Register HL (i.e., the keyboard driver address + a 43 byte offset) into the memory location 60A8H, which is the middle of an OPCODE.

6065

LD (TMPDCB),HL

Store the value held in Register HL (i.e., the keyboard driver address + a 43 byte offset) into the memory location 609BH, which is the middle of an OPCODE.

6068

POP HL

Put the value held at the top of the STACK (i.e., the keyboard driver address) into Restore Register Pair HL, and then remove the entry from the stack.

6069

EX DE,HL

Prepare for a LDIR by first EXchanging the value stored in Register Pair HL (i.e., the keyboard driver address) with the value stored in Register Pair DE; so now Register Pair DE holds the the keyboard driver address.

606A

LD HL,GOGO1

LET Register Pair HL = 60A6H, which is the “DO” Driver Routine.

606D

LD BC,GOGO4 – GOGO1

LET Register Pair BC = 0026H (Decimal: 38).

6070

LDIR

6072

POP HL

Put the value held at the top of the STACK (i.e., the pointer to the command line entered by the USER after the library command itself) into Restore Register Pair HL, and then remove the entry from the stack.

6073

LD DE,(MEMEND)

Fetch the value stored at memory location 4411H and put it into Register DE.
NOTE: 4411H is the storage location for the MEMORY PROTECT address.

6077
6078
6079

DEC D
DEC D
LD E,0E0H

Let Register Pair DE = 544 bytes before the end of RAM.

607B

LD (MEMEND),DE

Store the value held in Register DE into the memory location 4411H.
NOTE: 4411H is the storage location for the MEMORY PROTECT address.

607F

LD (MEM1),DE

Store the value held in Register DE into the memory location 40A0H.
NOTE: 40A0H is the storage location for the TOP OF FREE MEMORY.

6083

LD DE,(TMPDCB)

Fetch the value stored at memory location 609BH (i.e., the DCB address) and put it into Register DE.

6087

CALL SYNTAX
[441CH]

GOSUB to 441CH.
NOTE: 441CH is the SYS00/SYS routine to CHECK THE SYNTAX OF A FILESPEC before for use. This RST 28H’s with a value of C1H so as to call ROUTINE 4 in OVERLAY 1.

608A

JP NZ,ERR3
[5218H]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned because of an ERROR, JUMP to 5218H.

608D

LD HL,EXT5

LET Register Pair HL = 60CCH to point to a default file extension.

6090

CALL PUTEXT
[444BH]

GOSUB to 444BH to add the extension pointed to by Register Pair HL to the end of the filename pointed to by Register Pair DE.

The next few instructions calculate a buffer address.

6093

LD HL,(MEMEND)

Fetch the value stored at memory location 4411H and put it into Register HL.
NOTE: 4411H is the storage location for the MEMORY PROTECT address.

6096

LD DE,0020H

LET Register Pair DE = 0020H (Decimal: 32) for 32 characters.

6099

ADD HL,DE

LET Register Pair HL = Register Pair HL + Register DE.

609A

LD DE,TMPDBC

LET Register Pair DE = the value stored in memory location 609BH, which was put there elsewhere in this overlay. This is the DCB address.

609D

LD B,00H

LET Register B = 00H so as to set the file to a LRL = 0.

609F

CALL OPEN
[4424H]

GOSUB to 4424H.
NOTE: 4424H is the SYS00/SYS routine to OPEN A DISK FILE for use. This RST 28H’s with a value of 92H so as to call ROUTINE 1 in OVERLAY 3.

60A2

JP NZ,ERROR
[4409H]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned because of an ERROR, JUMP to 4409H.
NOTE: 4409H is the SYS00/SYS routine to process DOS errors.

60A5

RET

RETurn to the caller.

60A6H – “DO” Driver Routine.

This is the new keyboard routine and is moved to high ram. This restores the normal keyboard driver upon termination of the DO file. Once DO is started, there is no way to stop it, as the keyboard is no longer active.

“GOGO1”
60A6

PUSH DE

Save Register Pair DE (i.e., the DCB address) to the top of the stack.

60A7

LD DE,GODCB

LET Register Pair DE = the memory contents of 60A8H-60A9H which were put there elsewhere in this overlay. This will be the new DCB address.

60AA

CALL GET
[0013H]

GOSUB to 0013H.
NOTE: 0013H is the Model III ROM routine to read a byte from an input device. Requires DE = starting address of DCB of device and on Exit Register A = byte received from device, Z set if device ready. Uses AF.

60AD

JR Z,OKGO
[60B8H]

If the Z FLAG (Zero) is set then there was no error, so JUMP to 60B8H.

60AF

AND 0FEH

MASK the value of Register A against 0FEH (1111 1110). This has the effect of turning off Bit 0.

60B1

CP EEOF

Compare the value held in Register A against 1CH to see if there is an EOF ERROR. Results: If Register A equals 1CH, the Z FLAG is set; otherwise the NZ FLAG is set.

60B3

JP NZ,ERROR
[4409H]

If the NZ FLAG (Not Zero) is set, JUMP to 4409H.
NOTE: 4409H is the SYS00/SYS routine to process DOS errors.

60B6

JR GOGO3
[60BEH]

JUMP to 60BEH to terminate the “DO” Execution.

60B8H – Continuation of the “DO” Command. Jumped here if there was an error in getting characters.

“OKGO”
60B8

CP 0FFH

Compare the value held in Register A against 0FFH (i.e., EOF). Results: If Register A equals 0FFH, the Z FLAG is set; otherwise the NZ FLAG is set.

60BA

JR Z,GOGO3
[60BEH]

If the Z FLAG (Zero) is set then we have an EOF, so JUMP to 60BEH to terminate the “DO” Execution.

“GOGO2”
60BC

POP DE

Put the value held at the top of the STACK (i.e., the DCB address) into Restore Register Pair DE, and then remove the entry from the stack.

60BD

RET

RETurn to the caller.

60BEH – JUMP to 60BEH to terminate the “DO” Execution.

“GOGO3”
60BE

LD DE,(GOSAVE)

Fetch the value stored at memory location 42B1H (i.e., the saved driver address) and put it into Register DE.

60C2

LD (KDCB + 1),DE

Store the value held in Register DE (i.e., the saved driver address) into the memory location 4016H (i.e., the keyboard driver address).

60C6

XOR A

Set Register A to ZERO and clear all Flags.

60C7

LD (DOFLAG),A

Store the value held in Register A (i.e., 0) into the memory location 4CFDH (i.e., the flag indicating if “DO” is active).

60CA

JR GOGO2
[60BCH]

JUMP to 60BCH to restore the DCB address and RETurn.

60CCH – MESSAGE STORAGE AREA for “DO”.

60CCH
“EXT5”

DEFM …

“BLD“.

60CFH – “PAUSE” Library Command.

SPAUSE
60CF

PUSH HL

Save Register Pair HL (i.e., the pointer to the command line entered by the USER after the library command itself) to the top of the stack.

60D0

LD HL,PRESNY

LET Register Pair HL = 60F8H, which is a pointer to the message “PRESS <ENTER> TO CONTINUE“.

60D3

CALL PRINT
[021BH]

GOSUB to 021BH.
NOTE: 021BH will display the character at (HL) until a 03H is found.

60D6

LD A,(DOFLAG)

Fetch the value stored at memory location 4CFDH (i.e., the memory location storing whether the DO command is active or not) and put it into Register A.

60D9

OR A

Since a LD command does not set any FLAGS, Set FLAGS based on the contents of Register A.

60DA

JR NZ,SPAUS1
[60EAH]

If the NZ FLAG (Not Zero) is set, then the “DO” command is active, so JUMP to 60EAH.

60DC

PUSH BC

Save Register Pair BC to the top of the stack.

“SPAUS0”
60DD

LD B,01H

LET Register B = 01H, which is the number of characters we want to receive from the keyboard.

60DF

LD HL,0000H

LET Register Pair HL = 0000H to clear out the location where that character will be stored.

60E2

CALL KEYN
[0040H]

60E5

JR C,SPAUS0
[60DDH]

If the C FLAG (Carry) is set then the BREAK key was hit, so LOOP BACK to 60DDH and wait for another key.

60E7

POP BC

Put the value held at the top of the STACK (i.e., whatever BC was before this; didn’t matter) into Restore Register Pair BC, and then remove the entry from the stack.

60E8

POP HL

60E9

RET

RETurn to the caller.

60EAH – Continuation of the “PAUSE” Library Command, Jumped here if the “DO” command is active.

“SPAUS1”
60EA

CALL GETCR
[60EFH]

GOSUB to 60EFH to wait for an ENTER key.

60ED

POP HL

60EE

RET

RETurn to the caller.

60EFH – Continuation of the “PAUSE” Library Command. Subroutine to read the keyboard for an ENTER key.

“GETCR”
60EF

LD A,(3840H)

Fetch the value stored at memory location 3840H (i.e., the keyboard row with the ENTER key) and put it into Register A.

60F2

CP 01H

Compare the value held in Register A against 01H (i.e., the ENTER key). Results: If Register A equals the ENTER key, the Z FLAG is set; otherwise the NZ FLAG is set.

60F4

JR NZ,GETCR
[60EFH]

If the NZ FLAG (Not Zero) is set then we didn’t get the ENTER key, so LOOP BACK to the top of this routine at 60EFH and keep checking.

60F6

XOR A

Set Register A to ZERO and clear all Flags.

60F7

RET

RETurn to the caller.

60F8H – MESSAGE STORAGE AREA for “DO”.

“PRESNY”
60F8

DEFM …

“PRESS <ENTER> TO CONTINUE” + 0DH

“BUFPNT”

DEFW 00H

6114H – “ERROR” Library Command.

“EZZOR”
6114

CALL DECCHK
[541AH]

GOSUB to 541AH to convert a COMMAND LINE byte pair to decimal.

6117

JP NC,ERR2
[5214H]

If the NC FLAG (No Carry) is set then that routine returned with an error, so JUMP to 5214H.

611A

LD E,A

LET Register E = Register A (i.e., the requested error code).

611B

LD A,(HL)

Fetch the value stored at memory location (i.e., the next byte in the requested error code) pointed to by Register Pair HL (i.e., the pointer to the command line entered by the USER after the library command itself) and put it into Register A.

611C

CP 20H

Compare the value held in Register A against 20H (ASCII: SPACE). Results:

If Register A equals SPACE, the Z FLAG is set.
If A < SPACE, the CARRY FLAG will be set.
if A >= SPACE, the NO CARRY FLAG will be set.

611E

LD A,E

LET Register A = Register E (i.e., the requested error code).

611F

JR C,EZZO1
[6130H]

If the C FLAG (Carry) is set then Register A < SPACE, JUMP to 6130H.

6121

CALL DECCHK
[541AH]

>GOSUB to 541AH to convert a COMMAND LINE byte pair to decimal.

6124

JP NC,ERR2
[5214H]

If the NC FLAG (No Carry) is set then that routine returned with an error, so JUMP to 5214H.

6127

PUSH AF

Save Register Pair AF (i.e., the requested error code) to the top of the stack.

6128

LD A,E

LET Register A = Register E (i.e., the first digit of the requested error code).

6129

RLCA
RLCA

Let Register A = Register A * 4.

612B

ADD A,E

LET Register A = Register A + Register E, so Register A = original Register A * 5.

612C

RLCA

Rotate the bits in A left, so Register A = original Register A * 10.

612D

LD E,A

LET Register E = Register A, but moved to the TENS digit.

612E

POP AF

Put the value held at the top of the STACK (i.e., the requested error code) into Restore Register Pair AF, and then remove the entry from the stack.

612F

ADD A,E

LET Register A = Register A + Register E, so now we have both digits.

“EZZO1”
6130

OR 0C0H

OR Register A against 0C0H (1100 0000) to set the LONG ERROR MESSAGE bits (i.e., bits 7 and 6)

“ERRZ”
6132

JP ERROR
[4409H]

JUMP to 4409H.
NOTE: 4409H is the SYS00/SYS routine to process DOS errors.

6135H – Common Subroutine – Display or Print the Character held in Register A.

“PDATA”
6135

PUSH BC

Save Register Pair BC to the top of the stack.

6136

LD BC,(LPFLAG)

Fetch the value stored at memory location 5A4DH (i.e., the byte flag for PRINTER) and put it into Register BC.

613A

LD E,A

LET Register E = Register A (i.e., the character to output).

613B
613C

LD A,B
OR C

613D

LD A,E

LET Register A = Register E (i.e., the character to output).

613E

POP BC

Put the value held at the top of the STACK into Restore Register Pair BC, and then remove the entry from the stack.

613F

PUSH AF

Save Register Pair AF (i.e., the character to output) to the top of the stack.

6140

CALL NZ,PRT
[003BH]

If the NZ FLAG (Not Zero) is set, GOSUB to 003BH which is the Model III ROM routine to write the byte held in Register A to the printer, including waiting for the printer to be available OR getting a BREAK. Uses Register Pair DE.

6143

POP AF

Put the value held at the top of the STACK (i.e., the character to output) into Restore Register Pair AF, and then remove the entry from the stack.

6144

JP DSP
[0033H]

JUMP to 0033H.
NOTE: 0033H is the Model III ROM character print routine; displays the character held in Register A at the current cursor position.

6147H – Common Subroutine – Display or Print the message pointed to by Register Pair HL.

“PRT2”
6147

PUSH BC

Save Register Pair BC to the top of the stack.

6148

LD BC,(LPFLAG)

Fetch the value stored at memory location 5A4DH (i.e., the byte flag for PRINTER) and put it into Register BC.

614C
614D

LD A,B
OR C

614E

POP BC

Put the value held at the top of the STACK into Restore Register Pair BC, and then remove the entry from the stack.

614F

PUSH HL

Save Register Pair HL (i.e., the pointer to the the messsage to be displayed or printed) to the top of the stack.

6150

CALL NZ,LPRINT
[6157H]

If the NZ FLAG (Not Zero) is set, meaning that the printer flag was NZ, GOSUB to 6157H to output the message to the Printer.

6153

POP HL

Put the value held at the top of the STACK (i.e., the pointer to the the messsage to be displayed or printed) into Restore Register Pair HL, and then remove the entry from the stack.

6154

JP PRINT
[021BH]

JUMP to 021BH.
NOTE: 021BH will display the character at (HL) until a 03H is found.

6157H – Common Subroutine – Print a Message Pointed to by Register Pair HL, until a 03H or 0DH is reached.

“LPRINT”
6157

PUSH HL

Save Register Pair HL (i.e., the pointer to the messsage to be displayed or printed) to the top of the stack.

“LPRIN0”
6158

LD A,(HL)

Fetch the value stored at memory location (i.e., a character in the messsage to be displayed or printed) pointed to by Register Pair HL (i.e., the pointer to the messsage to be displayed or printed) and put it into Register A.

6159

CP 03H

Compare the value held in Register A against 03H, which is a standard terminator. Results: If Register A equals 03H, the Z FLAG is set; otherwise the NZ FLAG is set.

615B

JR Z,LPRIN1
[6165H]

If the Z FLAG (Zero) is set, meaning that we a terminator, JUMP to 6165H to restore HL from the STACK and RETurn.

615D

CALL PRT
[003BH]

GOSUB to 003BH which is the Model III ROM routine to write the byte held in Register A to the printer, including waiting for the printer to be available OR getting a BREAK. Uses Register Pair DE.

6160

INC HL

INCrement the value stored in Register Pair HL (i.e., the pointer to the messsage to be displayed or printed) by 1.

6161

CP 0DH

Compare the value held in Register A against 0DH (ASCII: CARRIAGE RETURN). Results: If Register A equals CARRIAGE RETURN, the Z FLAG is set; otherwise the NZ FLAG is set.

6163

JR NZ,LPRIN0
[6158H]

If the NZ FLAG (Not Zero) is set, JUMP to 6158H to continue looping through (HL) and printing the character until a 03H or 0DH is reached.

“LPRIN1”
6165

POP HL

Put the value held at the top of the STACK into Restore Register Pair HL (i.e., the pointer to the the messsage to be displayed or printed), and then remove the entry from the stack.

6166

RET

RETurn to the caller.

6167H – SUBROUTINE in the “DIR” Library Routine to Start Processing a @ (aka Pause) request.

"INKEY"
6167

CALL BRKCHK
[028DH]

GOSUB to 028DH.
NOTE: 028DH is the Model III ROM routine to CHECK FOR BREAK. On exit, the NZ FLAG will be set if BREAK was detected.

616A

JP NZ,ABORT
[4030H]

If the NZ FLAG (Not Zero) is set, meaning that the prior CALL routine returned because of an ERROR, JUMP to 4030H.
NOTE: 4030H is the OPERATION ABORTED routine. Routine runs, displays an error, and returns to the DOS PROMPT.

616D

CALL GETKBD
[6188H]

GOSUB to 6188H to scan the keyboard.

6170

OR A

Set FLAGS based on the contents of Register A.

6171

RET Z

If the Z FLAG (Zero) is set, RETurn to the caller.

6172

CP 40H

Compare the value held in Register A against 40H (ASCII: @). Results: If Register A equals (ASCII: @), the Z FLAG is set; otherwise the NZ FLAG is set.

6174

JR Z,HLDPAT
[617CH]

If the Z FLAG (Zero) is set because we got a @, JUMP to 617CH to actually deal with being paused.

6176

PUSH BC

Save Register Pair BC to the top of the stack.

6177

LD B,A

LET Register B = Register A (i.e., the key which was pressed).

6178

XOR A

Set Register A to ZERO and clear all Flags to clear any error status.

6179

LD A,B

LET Register A = Register B (i.e., the key which was pressed).

617A

POP BC

Put the value held at the top of the STACK into Restore Register Pair BC, and then remove the entry from the stack.

617B

RET

RETurn to the caller.

617CH - Continuation of the SUBROUTINE in the "DIR" Library Routine to Process a @ (aka Pause) keypress.

"HDLPAT"
617C

CALL KETKBD
[6188H]

GOSUB to 6188H to scan the keyboard.

617F

OR A

Set FLAGS based on the contents of Register A.

6180

JR Z,HLDPAT
[617CH]

If the Z FLAG (Zero) is set then no key was pressed so JUMP back to 617CH and keep polling.

6182

CP 0DH

Compare the value held in Register A against 0DH (ASCII: ENTER). Results: If Register A equals ENTER, the Z FLAG is set; otherwise the NZ FLAG is set.

6184

JR NZ,HLDPAT
[617CH]

If the NZ FLAG (Not Zero) is set then we still do not have a ENTER, JUMP back to 617CH and keep polling.

6186

XOR A

Set Register A to ZERO and clear all Flags.

6187

RET

RETurn to the caller.

6188H - Continuation of the SUBROUTINE in the "DIR" Library Routine to Process a @ (aka Pause) keypress. This part scans the keyboard, bypassing the DO command.

"GETKBD"
6188

LD A,(DOFLAG)

Fetch the value stored at memory location 4CFDH (i.e., to see if the "DO" command is active) and put it into Register A.

618B

OR A

Since a LD command does not set any FLAGS, Set FLAGS based on the contents of Register A.

618C

JP Z,KBD
[002BH]

If the Z FLAG (Zero) is set then the "DO" command is NOT active, JUMP to 002BH.
NOTE: 002BH is the Model III ROM Keyboard scanning routine; Register A exits with the ASCII value for the key that was pressed or ZERO if no key was pressed.

If we are here then we need an ACTUAL keypress, but DO is active; meaning that the keyboard is actually feeding from a disk file. With this we need to jump to a routine in ROM which reads the keyboard regardless of whether DO is active or not.

618F

PUSH BC

Save Register Pair BC to the top of the stack.

6190

PUSH DE

Save Register Pair DE to the top of the stack.

6191

PUSH HL

Save Register Pair HL to the top of the stack.

6192

PUSH IX

Save Register Pair IX to the top of the stack.

6194

LD IX,KDCB

LET Register Pair IX = 4015H, which is the real keyboard DCB, so as to ignore any DO command rerouting of the keyboard.

6198

CALL KEYBDZ
[3024H]

GOSUB to 3024H which is the Model III ROM Routine Vector to a routine to get keyboard input.

619B

POP IX

Put the value held at the top of the STACK into Restore Register Pair IX, and then remove the entry from the stack.

619D

POP HL

Put the value held at the top of the STACK into Restore Register Pair HL, and then remove the entry from the stack.

619E

POP DE

Put the value held at the top of the STACK into Restore Register Pair DE, and then remove the entry from the stack.

619F

POP BC

Put the value held at the top of the STACK into Restore Register Pair BC, and then remove the entry from the stack.

61A0

RET

RETurn to the caller.

61A1H - Part of the "CREATE" Library Command. Jumped here to insert a value into a message.

HEXS
61A1

PUSH AF

Save Register Pair AF to the top of the stack.

61A2
61A3
61A4
61A5

RLCA

Swap the lower nybble with the higher nybble by rotating the bits in A left (with Bit 7 going into both the CARRY and Bit 0) four times. This rotates bits 3, 2, 1, 0 into bits 7, 6, 5, 4 and bits 7, 6, 5, 4 into bits 3, 2, 1, 0.

61A6

CALL HEXS1
[61AAH]

GOSUB to 61AAH which is a nice space saving trick. It GOSUB's 2 instructions down, so the routine can easily handle the lower and upper nybble without a lot of extra code.

61A9

POP AF

Put the value held at the top of the STACK into Restore Register Pair AF (restoring the original Register A), and then remove the entry from the stack.

"HEXS1"
61AA

AND 0FH

MASK the value of Register A against 0FH (0000 1111). This has the effect of turning off bits 7, 6, 5, 4, leaving only bits 3, 2, 1, 0 active.

Another DAA set ... Never been able to find a good source to clearly explain this. It is converting a decimal value into a binary coded decimal value.

61AC

ADD A,90H

LET Register A = Register A + 90H. Since Register A's possible value is 0-F, this changes Register A's possible values to 90H-9FH.

61AE

DAA

Adjust Register A for BCD addition and subtraction operations. DAA is way too complicated to go into here, but if the low 4 bits are greater than 9, the H FLAG is set and 06H is addded to Register A and if the high 4 bits are greater than 9, the C FLAG is set and 60H is added to Register A. The explanation for this is that there are 6 ASCII characters between 9 and A, so adding 6H (for the ones digit) or 60H (for the tens digit), changes A-F into 10-15 in decimal.

61AF

ADC A,40H

61B1

DAA

61B2

LD (HL),A

Store the value held in Register A (which is the converted character) into the memory location pointed to by Register Pair HL (i.e., the location in the message text into which to put the character).

61B3

INC HL

INCrement the value stored in Register Pair HL by 1 (i.e., the NEXT location in the message text).

61B4

RET

RETurn to the caller.

61B5H - Part of the "DIR" Library Command to convert a value held in Register A (which is either FILE CREATION MONTH or FILE CREATION YEAR as extracted from a files directory entry) and place it in the middle of the message " 00/00", in the specific the location pointed to by Register Pair HL. Routine is called once with MONTH and then once with YEAR.

"HEXAAS"
61B5

LD (HL),2FH

Store the character which precedes 0 into the memory location pointed to by Register Pair HL.

"HEXAA1"
61B7

INC (HL)

Top of a loop. Bump the character pointed to by HL by 1 (so on initial run, this will start at 0 being placed in the message for a leading zero (i.e., if the initial character for a month is below 10).

61B8

SUB 0AH

SUBtract the value 0AH from Register A (i.e., the byte containing either the file creation MONTH or file creation YEAR from the file's directory sector).

61BA

JR NC,HEXAA1
[61B7H]

If the NC FLAG (No Carry) is set, meaning that the subtraction didn't fall below 0, JUMP to 61B7H. If this is the month, then it will jump on months 1-9, and not jump on months 10-12.

61BC

ADD A,3AH

LET Register A = Register A + 3AH. When 3AH is added to -9 (i.e., January) through -1 (i.e, September), it turns into the ASCII versions of "1"-"9".

61BE

INC HL

INCrement the value stored in Register Pair HL by 1 so as to point to the next character in the message to overwrite.

61BF

LD (HL),A

Store the value held in Register A into the memory location pointed to by Register Pair HL (i.e., a specific location in a message).

61C0

RET

RETurn to the caller.

61C1H - Part of the "DIR" Library Command to display the contents of Register Pair HL in decimal form.

"BINDEC"
61C1

LD A,20H

LET Register A = 20H (ASCII: SPACE).

61C3

LD B,02H

LET Register B = 02H for a loop of 2 times.

"L6OP30"
61C5

CALL PDATA
[6135H]

GOSUB to 6135H to display or print the byte held in Register A (i.e., a character of the filename); routine affects Registers A and E.

61C8

DJNZ L6OP30
[61C5H]

LOOP back to 61C5H, reducing Register B each time, and continue to LOOP until Register B has been reduced to ZERO, in which case, continue with the next instruction. This will have displayed and/or printed two SPACE characters.

"BINDC1"
61CA

CALL 0A9AH
[0A9AH]

GOSUB to 0A9AH.
NOTE: 0A9AH is the Model III ROM routine to STORE AN INTEGER. The value in HL is put into the single precision number storage area of 4121H and is flagged as an INTEGER.

61CD

XOR A

Set Register A to ZERO and clear all Flags.

61CE

CALL 1034H
[1034H]

GOSUB to 1034H in the Model III ROM. This routine prepares for the conversion of Register A into ASCII. Register Pair HL is modified.

61D1

OR (HL)

OR the value stored at (HL) against Register A. The results are stored in Register A.

61D2

CALL 0FD9H
[0FD9H]

GOSUB to 0FD9H in the Model III ROM. This routine finishes the conversion of Register A into ASCII.

61D5

LD HL,4131H

LET Register Pair HL = 4131H which is the memory location holding the converted number.

"L6OP25"
61D8

LD A,(HL)

Fetch the value stored at memory location (i.e., the ASCII character for that number) pointed to by Register Pair HL and put it into Register A.

61D9

OR A

Since a LD command does not set any FLAGS, Set FLAGS based on the contents of Register A.

61DA

RET Z

If the Z FLAG (Zero) is set then we have an END OF STRING, so RETurn to the caller.

61DB

CALL PDATA
[6135H]

GOSUB to 6135H to output the character held in Register A.

61DE

INC HL

INCrement the value stored in Register Pair HL by 1 so as to point to the next memory location to be converted.

61DF

JR L6OP25
[61D8H]

LOOP back to 61D8H and keep going until exited by hitting a 0.

61E1H - Message Storage Area for TIME and DATE DISPLAY.

"DPRT1"
61E1

DEFM '00'

"DELIM1"
61E3

DEFM ':'

"DPRT2"
61E4

DEFM '00'

"DELIM2"
61E6

DEFM ':'

"DPRT3"
61E7

DEFM '00' + 0DH

61EAH - Display TIME$ and DATE$. This routine is called by both the DATE and TIME library commands, and Register C holds the delimter character of either / or :.

"MSGPRT"
61EA

CALL MSGPR0
[61F0H]

GOSUB to 61F0H to generate the text line of xx/xx/xx or yy:yy:yy.

61ED

JP PRINT
[021BH]

JUMP to 021BH.
NOTE: 021BH will display the character at (HL) until a 03H is found and then RETurn to this routines caller (since JUMP was used instead of CALL).

61F0H - Part of the "DATE" and "TIME" Library Commands. This generates the text line of xx/xx/xx or yy:yy:yy.

"MSGPR0"
61F0

LD A,C

LET Register A = Register C (i.e., the / or :).

61F1

LD (DELIM1),A

Store the value held in Register A into the memory location 61E3H, which is the first delimter in the 00:00:00 message stored at 61E1H.

61F4

LD (DELIM2),A

Store the value held in Register A into the memory location 61E6H, which is the second delimter in the 00:00:00 message stored at 61E1H.

61F7

LD IX,HOUR

LET Register Pair IX = 4219H, which is the memory location holding the HOUR.

61FB

CP 3AH

Compare the value held in Register A against 3AH (ASCII: :) to see if we are processing the TIME or the DATE. Results: If Register A equals 3AH :, the Z FLAG is set; otherwise the NZ FLAG is set.

61FD

JR Z,MSGPR1
[6203H]

If the Z FLAG (Zero) is set then we are processing the TIME, so JUMP to 6203H.

61FF

LD IX,MONTH

LET Register Pair IX = 421CH, which is the memory location holding the MONTH.

"MSGPR1"
6203

LD HL,DPRT1

LET Register Pair HL = 61E1H, which is the pointer to the message "00:00:00".

6206

LD B,03H

LET Register B = 03H for a DJNZ loop of 3 sets of numbers to copy.

"MSGPR2"
6208

LD A,(IX+00H)

Fetch the value stored at the memory location pointed to by IX+00H (i.e., the current location of the "00:00:00" message) and put it into Register A.

620B

CALL HEXCOV
[5E46H]

GOSUB to 5E46H to convert this into a two digit decimal number.

620F
620E

INC HL
INC HL

INCrement the value stored in Register Pair HL by 2 character locations.

6210

DEC IX

DECrement the value stored in Register Pair IX by 1 so as to point to the next number.

6212

DJNZ MSGPR2
[6208H]

LOOP back to 6208H, reducing Register B each time, and continue to LOOP until Register B has been reduced to ZERO, in which case, continue with the next instruction.

6214

LD HL,DPRT1

LET Register Pair HL = 61E1H, which is the pointer to the message "00:00:00".

6217

RET

RETurn to the caller.

6218H - Routine to READ A RECORD from FILE 1.

"REDIT"
6218

PUSH BC

Save Register Pair BC to the top of the stack.

6219

CALL GETDCB
[622BH]

GOSUB to 622BH to set the variables for the following JUMP.

621C

CALL READ
[4436H]

GOSUB to 4436H.
NOTE: 4436H is the SYS00/SYS vector for 'READ', which reads the record that the disk drive is positioned over.

621F

POP BC

Put the value held at the top of the STACK into Restore Register Pair BC, and then remove the entry from the stack.

6220

RET Z

If the Z FLAG (Zero) is set, then there was no error returned from the READ VECTOR call, so RETurn to the caller.

6221

POP HL

If we're here, there was an error so ... first, empty the stack.

6222

JP 6132H
[6132H]

and then exit with a JUMP to 6132H.

6225H - Routine to OPEN from FILE 1.

"OPENIT"
6225

CALL GETDCB
[622BH]

GOSUB to 622BH to set the variables for the following JUMP.

6228

JP OPEN
[4424H]

JUMP to 4424H.
NOTE: 4424H is the SYS00/SYS routine to OPEN A DISK FILE for use. This RST 28H's with a value of 92H so as to call ROUTINE 1 in OVERLAY 3.

622BH - Routine to Set the Variables Needed for a JUMP to 4424H.

"GETDCB"
622B

LD B,00H

LET Register B = 00H to signify a LRL of 0.

"GETDC1"
622D

LD DE,S6DCB1

LET Register Pair DE = 6280H as the applicable DCB.

6230

LD HL,S6BUF1

LET Register Pair HL = 6300H as the applicable RAM BUFFER.

6233

RET

RETurn to the caller.

6234H - Routine to CREATE FILE 1.

"INITIT"
6234

CALL GETDCB
[622BH]

GOSUB to 622BH to set the variables for the following JUMP.

6237

JP INIT
[4420H]

JUMP to 4420H.
NOTE: 4420H is the SYS00/SYS routine to INITIALIZE A FILE (i.e., CREATE or OPEN). This RST 28H's with a value of A2H so as to call ROUTINE 2 in OVERLAY 2. Register HL needs to point to a RAM BUFFER for the DCB's.

623AH - Routine to CHECK FILE 1.

"GETSYN"
623A

LD DE,S6DCB1

LET Register Pair DE = 6280H as the applicable DCB.

623D

JP SYNTAX
[441CH]

JUMP to 441CH.
NOTE: 441CH is the SYS00/SYS routine to CHECK THE SYNTAX OF A FILESPEC before for use. This RST 28H's with a value of C1H so as to call ROUTINE 4 in OVERLAY 1.

END 5200H