Model III ROM Explained - Part 4 (Durda ROM)

Introduction

When Frank Durda IV passed away, his wife provided his collection to various archivists in the TRS-80 community. A Model 4 in that collection had a ROM which was under development by Frank and was never released to the public. That ROM had a "1(24) January 1986" label. This page is a disassembly of that ROM (and the other Model III ROM pages have been updated to account for Franks changes as alternative code), noting that the following are my findings:

Since the Model III ROM tried to stay as close to the Model I ROM as possible, legacy bytes were still present in unused areas. Frank NOP'd them all.
Moved as much code as possible from the end of the Model III ROM into the beginning of the Model III ROM. This was assisted by moving the PRINT SCREEN code out and by replacing a hidden name of "RON" in the code with the "CASS?" prompt. There were a bunch of changes in 0000H-0FFFH to accomplish this.
Freed over 300 bytes in the 3000H-37FFH range by removing all the code which set out the keyboard map/translation tables and the printer translation table. He used bit manipulation instead of table lookups.
Raised the base address for a SYSTEM cassette to be 42E8H instead of 4288H which stopped the SYSTEM tape from overwriting a LOT of Model III DOS RAM locations.
Fixed 2 Bugs in the Model III ROM:
- Hitting BREAK at the filename inquiry of a SYSTEM command would reboot a Model III due to a bug in 02C3H-02C5H. This ROM returns to the READY prompt.
- Fixing a failure to tag an instruction as DATA because a byte was written to the wrong memory location (1BC1-1BC3, 1BDC-1BDE, and 1C67-1C69). This fix was the only change he made between ROM Address 1000H and 2FFFH
Implemented code at 304BH to permit a boot from a Network 4 Controller which seem to be accessed by answering a number at the CASS? prompt other than 3 or 5.
Implemented code at 316AH to permit a boot from a Hard Drive.
Implemented code at 379CH which addressed hardware sitting at ports 30, 32, 33, 38, and 39
Hid his initials in the ROM C
Really streamlined some code to make all the above fit. Examples would be that if a routine needed to output a 0 to some ports and then a 1 to others, he would do those in that order with a BUMP or a XOR, or using the opcode LD (HL),00H instead of loading A with 0 first. He also broke out a few new memory addresses where he stored stuff.

3000 - Jump Table.

3000

JP 325CH

JUMP to 325CH for a SLOW tape header write.

3003

JP 3299H

JUMP to 3299H for a FAST tape header write.

3006

JP 3272H

JUMP to 3272H for a SLOW tape header read.

3009

JP 32D8H

JUMP to 32D8H for a FAST tape header read.

300C

JP 31C0H

JUMP to 31C0H for Cassette OFF.

300F

JP 31D1H

JUMP to 31D1H for Cassette ON.

3012

JP 30C3H

JUMP to 30C3H for Warm Boot.

3015

JP 30A2H

JUMP to 30A2H for Bootstrap.

3018

JP 35C3H

JUMP to 35C3H for Maskable Interrupt Handler.

301B

JP 3601H

JUMP to 3601H for RS-232 Initialization.

301E

JP 364AH

JUMP to 364AH for RS-232 Input.

3021

JP 3676H

JUMP to 3676H for RS-232 Output.

3024

JP 338CH

JUMP to 338CH for Keyboard Input.

3027

JP 3781H

JUMP to 3781H for Print Screen Routine.

302A

JP 31F7H

JUMP to 31F7H for Print# Processing

302D

JP 3739H

JUMP to 3739H for a routine which parses whether the current instruction on a the current line is in quotes.

3030

JP 37EAH

JUMP to 37EAH for a routine which allows BASIC TIMES (DATE$+" "+TIME$)

3033

JP 35BCH

JUMP to 35BCH to put the DATE onto the upper right hand corner of the screen.

3036

JP 35A1H

JUMP to 35A1H to put the TIME 10 characters from the upper right hand corner of the screen.

3039

JP 4049H

JUMP to 4049H which is the NMI RST Vector

303C-303F - Frank Durda IV's Initials

303C-303F

"FDIV"

Frank Durda IV's Initials

3040-3047 - No Location Jumps Here. This may have been a Frank Durda Embedded Serial Number of 98 36 C3 7D 30 C3 6A 37.

3040

SBC A,B

Subtract Register B and the CARRY FLAG from Register A.

3041

LD (HL),C3H

Put a C3H into the memory location pointed to by (HL)

3043

LD A,L

Let Register A = Register L

3044

JR NC,3009H

If the SBC command in 3040H did not produce a CARRY FLAG, JUMP to 3009H

3045

JP 376AH

** Z-80 TRICK ** - I guess Frank wanted to do one! If you jump to 3045H you are jumping into the middle of the instruction at 3044H, but that turns into this JUMP.

3046

LD L,D

If the SBC command in 3040H did produce a CARRY FLAG, Let Register L = Register D.

3047

SCF

Set the CARRY FLAG.

3048 - This subroutine is called by the print routine when a LINE FEED or CARRIAGE RETURN is the current character.

3048

JP 376AH

JUMP to 376AH.

304B - Part of the Network 4 Controller Boot - GOSUB'ed by 3076H and 30ECH

304B

LD A,(3810H)

Put the contents of 3810H into Register A.
NOTE: 3810H is the row of the keyboard matrix holding 0 through 7.

304E

BIT 3,A

Check Bit 3 of A. Bit 3 of 3810H will be on only for the 3 key.

3050

JP NZ,34E5H

If the key pressed is not a 3 then JUMP to 34E5H

3053

AND 10H

MASK A against 10H (Binary: 0001 0000) to leave only Bit 5 so as to check to see if a 5 key was pressed.

3055

JP Z,028DH

If a 5 key was pressed, JUMP to 028DH to check for a BREAK key.

3058

POP BC

Restore the STACK into Register Pair BC

Now we need to configure the Netork 4/Omninet

3059

XOR A

Zero Register A.

305A

OUT (0D1H),A

Output the contents of Register A to Port D1H which is the LSB of the Network 4/Omninet pointer.

305C

LD A,08H

Let A = 08H.

305E

OUT (0D3H),A

Output the contents of Register A to Port D3H which is the MSB of the Network 4/Omninet pointer

Next we load the Netork 4/Omninet boot code to 7000H in RAM

3060

LD BC,00D0H

LET BC = 00D0H. This is setting us up for B=0 as a counter, and C=D0H as a port. D0H is the Network 4/Omninet port for Input/Output with Automatic Increment

3063

LD HL,7000H

LET HL = 7000H

3066

PUSH HL

Save the value in HL to the STACK

3067

INIR

This command takes a byte from Port C (D0H) and writes it to the memory location pointed to by (HL). HL is then incremented, and B is decremented. If B is not zero, this operation is repeated. Interrupts can fire during this command.

3069

DEC A

Decrement A by 1.

306A

JR NZ,3067H

If Register A is NOT ZERO then JUMP to 3067H.

306C

LD HL,7300H

If we are here, then A was ZERO, so lets LET HL = 7300H, which is the memory location of the NETWORK 4 ROM.

306F - This tests to see if the first byte of the RAM address to pass control to (4300H for Floppy or Hard Drive, 7300H for Network 4) is a FDH. If not, we have a problem and RETURN, with NZ set. Ohterwise, Bump the starting memory address beyond that first byte, and JUMP to it to pass control to that BOOT CODE.

306F

LD A,(HL)

LET A = the memory contents of (HL).

3070

CP FDH

Compare Register A against FDH. Results:

If A=FDH it sets the ZERO FLAG
If A<FDH then the CARRY FLAG will be set
if A>=FDH then the NO CARRY FLAG will be set.

3072

RET NZ

If A is NOT FDH then RETURN out of the routine.

3073

POP DE

If we are here then A = FDH, so restore the STACK back into Register Pair BC.

3074

INC L

LET L = L + 1

3075

JP (HL)

JUMP to the memory location held in (HL).

304B - Part of the Network 4 Controller Boot - This was JUMPed to from 30EAH. This routine appears to process the CASS? answer, but beyond just H and L.

3076

CALL 304BH

GOSUB to 304BH, above.

3079

LD HL,0075H

HL = 0075H. 30EFH and 3100H jump here, but it can also be a pass through.

307C

PUSH HL

Save HL to the STACK.

307D

LD HL,05D1H

HL = 05D1H, which is the location in ROM of the "CASS?" prompt.

3080

CALL 309CH

GOSUB down to 309CH (which GOSUBs to 021BH [to display the message pointed to by HL] and then JUMPS to 0049H)

3083

CALL 0033H

GOSUB to 0033H to display the character held in Register A at the current cursor position.

3086

SUB 4CH

SUBtract 4CH (ASCII: "L") from Register A.

3088

LD (4211H),A

Set the Model III Cassette Baud by putting A (which is either 0 if "L" was hit, something else if anything else was hit) into (4211H).

308B

JR Z,3092H

If the subtraction set Register A at zero (meaning "LOW" speed was selected at the CASS? prompt, JUMP down a few instructions to 3092H to display the L, restore AF from the STACK, and RETURN.

308D

CP C1H

If we are here, a key response other than L was entered at the "CASS?" prompt, so lets COMPARE Register A against C1H. Results:

If A=C1H it sets the ZERO FLAG
If A<C1H then the CARRY FLAG will be set
if A>=C1H then the NO CARRY FLAG will be set.

308F

RET Z

If the modified Register A was C1H then RETURN.

3090

CP FCH

If we are here, then Register A was not 0 and was not C1H, so lets COMPARE Register A against FCH. Results:

If A=FCH it sets the ZERO FLAG
If A<FCH then the CARRY FLAG will be set
if A>=FCH then the NO CARRY FLAG will be set.

3092

PUSH AF

Save Register Pair AF to the STACK so we can use A in the next 2 instructions.

3093

LD A,0DH

LET A = 0DH (ASCII: Carriage Return).

3095

CALL 0033H

GOSUB to 0033H to display the character held in Register A at the current cursor position.

3098

POP AF

Restore AF from the STACK

3099

JR NZ,307DH

LOOP back to 307DH until the ZERO FLAG is set.

309B

RET

RETURN.

309C - This subroutine will display the message held in HL and then JUMP to the KBWAIT (Wait for Keypress) Routine.

309C

CALL 021BH

GOSUB to 021BH to display the message pointed to by HL.

309F

JP 0049H

JUMP to 0049H which RETURNS as soon as any key on keyboard is pressed, with Register A holding the ASCII value for character pressed.

30A2 - This is a VECTOR JUMP from 3015H - It resets all the ports, sets the interrupt to jump to 4046H, moved 76 bytes from 36AAH to 4000H, and reads disk sectors into 4000H+ until the interrupt fires.

30A2

IM 1

Set the INTERRUPT MODE to 1.

30A4

LD SP,407DH

Set up stack pointer to point to 407DH.

30A7

OUT (0E4H),A

Send the value held in Register A to Port E4H which is the Non-Maskable Interrupt Latch. Sending a 0 to E4 will turn off all Non-Maskable Interrupts.

30A9

CALL 379CH

GOSUB to 379CH.

30AC

LD HL,37E6H

Let HL = 37E6H which will be the memory location that Port 89H feeds.

30AF

LD A,0FH

Let A = 0FH (Decimal: 15) as A will be a counter

30B1

LD C,89H

Let C = 89H as the Port which will feed (HL)

30B3

OUT (88H),A

Send the value held in Register A to Port 88H which is the CRT Controller Control Register..

30B5

OUTD

This command takes the byte held in the memory location pointed to by HL and writes it to Port C. HL and B are then both decremented.

30B7

DEC A

Decrement A

30B8

JP P,30B3H

If A is still positive, then LOOP back up to 30B3H.

30BB

LD A,38H

Let A = 38H.

30BD

OUT (0ECH),A

Output 38H (Binary: 0011 1000) to Port ECH.
NOTE: Port ECH stores miscellaneous controls.

Bit 3: Alt. char. [0 = disable, 1 = enable]
Bit 4: I/O bus [0 = disable, 1 = enable]
Bit 5: Video waits [0 = disable, 1 = enable] ? Model 4 ONLY
Bit 6: CPU clock speed [0 = 2 mhz, 1 = 4 mhz]

30BF

LD A,04H

Let A = 04H (Binary: 0000 0100).

30C1

OUT (0E0H),A

OUTput 04H (Binary: 0000 0100) to Port E0H which stores the Maskable Interrupt. By sending Bit 2 HIGH, that chooses 4046H as the Maskable Interrupt Jump

30C3 - This is in the middle of the machine setup routine - While this is a pass through to set up the machine / warm boot, it is also a jump point for a failure to boot from anything AND is a VECTOR jump from 3012H.

30C3

LD A,81H

Let A = 81H

30C5

OUT (0F4H),A

OUTput 81H (Binary: 10000001) to Port F4H which is the Floppy drive select and options register. For OUTPUT:

Bit 0: Drive 0 Select
Bit 1: Drive 1 Select
Bit 2: Drive 2 Select
Bit 3: Drive 3 Select
Bit 4: Side Select (0 = Select Side 0, 1 = Select Side 1)
Bit 5: Write Precompensation (0 = Disable WP, 1 = Enable WP)
Bit 6: Wait State Generation (0 = Disable WSG, 1 = Enable WSG)
Bit 7: Density Select (0 = Single/FM, 1 = Double/MFM)

30C7

OUT (0E8H),A

OUTput 81H (Binary: 10000001) to Port E8H which is the RS-232 Status Register and Master Reset. Outputting ANYTHING to this port will reset the RS-232.

30C9

LD A,6FH

Let A = 6FH

30CB

OUT EAH,A

OUTput 6FH (Binary: 0110 1111) to Port EAH.
NOTE: Port EAH is the RS-232 UART Control Register/Status Register. For output:

Bit 0: Data Terminal Ready
Bit 1: Request to End
Bit 2: Break
Bit 3: Parity Enable
Bit 4: Stop Bits
Bit 5: Select
Bit 6: Word Length
Bit 7: Parity (0=Odd, 1=Even)

30CD

LD HL,36AAH

Let HL = 36AAH

30D0

LD DE,4000H

let DE = 4000H

30D3

LD BC,004CH

Let BC = 004CH (Decimal: 76 Bytes)

30D6

LDIR

Moves the byte from (HL) to (DE), then HL and DE are incremented, and BC is decremented until BC is zero. Interrupts CAN fire during this command.

30D8

LD A,0CH

Let A = 0CH

30DA

OUT (0F0H),A

Send 0CH (Binary: 0000 1100) to port F0H which is the Floppy Disk Command/Status Register. 0000 1100 is the command to RESTORE (0000), LOAD HEAD AT THE BEGINNING (1), VERIFY ON (1), 6ms STEP (00).

30DC

LD DE,41E2H

LET DE = 41E2H

30DF

LD C,46H

LET C = 46H (Decimal = 70).

30E1

LDIR

Moves the byte from (HL) to (DE), then HL and DE are incremented, and BC is decremented until BC is zero. HL is 365EH. Interrupts CAN fire during this command.

30E3

CALL 3518H

GOSUB to 3518H to initials the Port 84H settings

30E6

IN A,(0F0H)

INput from Port F0H which is the FDC Status port on input. Input Results:

Bit 0: Busy
Bit 1: Index/DRQ
Bit 2: Track 0/Data Lost
Bit 3: CRC error
Bit 4: Seek error/Record not found
Bit 5: If Reading, Record Type, if Writing, Write Fault/Head loaded
Bit 6: Write Protect
Bit 7: Not ready

30E8

LD C,A

Let Register C = Register A.

30E9

INC A

Increment A

30EA

JR Z,3076H

If A is ZERO (meaning that Port F0H returned FFH), JUMP to 3076H

30EC

CALL 304BH

If A wasn't ZERO, then GOSUB to 304BH

30EF

JR NZ,3079H

If the NOT ZERO flag is set, JUMP to 3079H.

30F1

IN A,(0F0H)

INput from Port F0H which is the FDC Status port on input. Input Results:

Bit 0: Busy
Bit 1: Index/DRQ
Bit 2: Track 0/Data Lost
Bit 3: CRC error
Bit 4: Seek error/Record not found
Bit 5: If Reading, Record Type, if Writing, Write Fault/Head loaded
Bit 6: Write Protect
Bit 7: Not ready

30F3

LD C,A

Let Register C = Register A.

30F4

BIT 2,A

Test Bit 2 of Register A. That Bit is for "TRACK 0 FOUND".

30F6

JR Z,30F9H

If Bit 2 of Register A is LOW, then skip the next instruction and JUMP to 30F9H.

30F8

LD B,A

Let Register B = Register A

30F9

AND 81H

MASK Register A against 81H (Binary: 1000 0001) to keep only Bits 0 and 7, which would be BUSY and NOT READY.

30FB

DEC A

Decrement Register A by 1. By doing this, a Port 81H status of NOT BUSY and NOT READY will return a ZERO FLAG.

30FC

JR Z,30ECH

If the Decremented Register A is ZERO, then JUMP to back to 30ECH to keep polling the drive.

30FE

LD A,B

Let Register A = Register B

30FF

OR A

Set the Flags for Register A

3100

JP Z,3079H

If A was ZERO, then JUMP back to 3079H to trigger the "CASS?" routine.

3103

Disable Interrupts

3104

LD A,C

Let Register A = Register C

3105

AND 98H

MASK Register A against 98H (Binary: 1001 1000) to keep only Bits 3, 4, and 7 (which are CRC ERROR, SEEK ERROR, and NOT READY).

3107

JR NZ,314EH

If none of those 3 errors are present, then JUMP to down to 314EH which tests for a Hard Drive.

3109

LD D,03H

If we are here, then we have either a CRC ERROR, SEEK ERROR, or NOT READY. Let Register D = 03H.

310B

LD A,81H

Let Register A = 81H.

310D

OUT (0F4H),A

OUTput 81H (Binary: 10000001) to Port F4H which is the Floppy drive select and options register. For OUTPUT:

Bit 0: Drive 0 Select
Bit 1: Drive 1 Select
Bit 2: Drive 2 Select
Bit 3: Drive 3 Select
Bit 4: Side Select (0 = Select Side 0, 1 = Select Side 1)
Bit 5: Write Precompensation (0 = Disable WP, 1 = Enable WP)
Bit 6: Wait State Generation (0 = Disable WSG, 1 = Enable WSG)
Bit 7: Density Select (0 = Single/FM, 1 = Double/MFM)

310F

DEC A

Decrement Register A (so make Register A = 80H or 1000 0000.

3110

OUT (0E4H),A

Send a Bit 7 HIGH to Port E4H which is the Non-Maskable Interrupt Latch. Sending a Bit 7 HIGH to E4 will ENABLE INTRQ Interrupts.

3112

LD HL,313BH

LET HL = 313BH

3115

LD (404AH),HL

Put 313BH into (404AH) and (404BH)

3118

LD A,0C3H

Let A = C3H

311A

LD (4049H),A

Put C3H into (4049H).
NOTE: 4049H is the RST 0 NMI Vector.

311D

LD C,0F3H

Let C = F3H.
NOTE: Port F3H is the FDC Data Register (the data byte to be READ or WRITTEN to disk).

311F

LD HL,4300H

Let HL = 4300H, which is the standard memory location for loading a BOOT sector into.

3122

LD A,01H

Let A = 01H

3124

OUT (0F2H),A

OUTput 01H to Port F2H which is the Floppy Disk Sector Register, telling the FDC we want to deal with Sector 1.

3126

LD A,80H

Let A = 80H

3128

CALL 37BBH

GOSUB to 37BBH

312B

IN A,(0F0H)

INput from Port F0H which is the FDC Status port on input. Input Results:

Bit 0: Busy
Bit 1: Index/DRQ
Bit 2: Track 0/Data Lost
Bit 3: CRC error
Bit 4: Seek error/Record not found
Bit 5: If Reading, Record Type, if Writing, Write Fault/Head loaded
Bit 6: Write Protect
Bit 7: Not ready

312D

AND 02H

MASK the results of Port F0H with 02H (Binary: 0010) so that only Bit 1 (Index) is live.

312F

JR Z,312BH

If Bit 1 of F0H (the Index) is LOW, JUMP to 312BH.

3131

INI

Read a byte from Port C into the memory location pointed to by HL, then DECrement HL and INCrement B. Z is set if B ? 1 = 0; otherwise it is reset.

3133

LD A,C1H

LET A = C1H (Binary: 1100 0001)

3135

OUT (0F4H),A

OUTput C1H (Binary: 1100 0001) to Port F4H which is the Floppy drive select and options register. For OUTPUT:

Bit 0: Drive 0 Select
Bit 1: Drive 1 Select
Bit 2: Drive 2 Select
Bit 3: Drive 3 Select
Bit 4: Side Select (0 = Select Side 0, 1 = Select Side 1)
Bit 5: Write Precompensation (0 = Disable WP, 1 = Enable WP)
Bit 6: Wait State Generation (0 = Disable WSG, 1 = Enable WSG)
Bit 7: Density Select (0 = Single/FM, 1 = Double/MFM)

3137

INI

Read a byte from Port C into the memory location pointed to by HL, then DECrement HL and INCrement B. Z is set if B ? 1 = 0; otherwise it is reset.
NOTE: Port C1H is the hard drive controller board control register. Sending a 0 resets the hard drive controller board.

+ 3139

JR 3135H

LOOP back to to 3135H.
NOTE: Ultimately an interrupt will fire and pull us out of this seemingly endless loop.

313B - This routine will clear the stack, check the floppy drive status register after a read, and JUMP to 4300H to continue to DOS if successful, and jump to 310BH if errors were found.

313B

POP HL

Clear the STACK (since HL is about to be overwriten)

313C

LD HL,45EDH

LET HL = 45EDH

313F

LD (4049H),HL

Put 45EDH into (4049H)

3142

IN A,(0F0H)

INput from Port F0H which is the FDC Status port on input. Input Results:

Bit 0: Busy
Bit 1: Index/DRQ
Bit 2: Track 0/Data Lost
Bit 3: CRC error
Bit 4: Seek error/Record not found
Bit 5: If Reading, Record Type, if Writing, Write Fault/Head loaded
Bit 6: Write Protect
Bit 7: Not ready

3144

AND 1CH

MASK the input from Port F0H against 1CH (Binary: 0001 1100) to keep only Bits 2, 3, and 4; all 3 of which are read errors (2: Computer did not respond to DRQ in time, 3: Error in ID Field, 4: Desired disk location not found).

3146

OUT (0E4H),A

Send the MASKED input to Port E4H which is the Non-Maskable Interrupt Latch. Since the MASKed A will have Bit 6 and 7 LOW, this DISABLES the DRQ and INTRQ interrupts.

3148

JP Z,4300H

If A was ZERO (meaning, none of those errors were present), JUMP to 4300H to run DOS.

314B

DEC D

Decrement D

314C

JR NZ,310BH

If A is NOT ZERO (which it HAS to be since we didn't jump away 2 instructions ago), JUMP to 310BH to try the disk read again.

314E - Hard Drive Routine - This routine is jumped from 3107H if the last disk read did not produce any of CRC ERROR, SEEK ERROR, and NOT READY.

314E

CALL 37CDH

GOSUB to 37CDH

3151

LD A,01H

LET A = 01H

3153

OUT (0CBH),A

OUTPUT the sector (held in A, from C) to Port CBH.
NOTE: Port CBH is Register 3 for WD1010 Winchester Disk Controller Chip which is the Hard Disk Sector Number Register.

3155

IN A,(0CBH)

Poll Port CBH and put the results into A.
NOTE: Port CBH is Register 3 for WD1010 Winchester Disk Controller Chip which is the Hard Disk Sector Number Register.

3157

DEC A

Decrement A

3158

JR NZ,3194H

If the decremented Register A is still not 0, then JUMP to 3194H

If we are here, A = 0

315A

OUT (0CEH),A

OUTPUT the contents of A to Port CEH which is Register 6 for WD1010 Winchester Disk Controller Chip which is the register contaning Hard Disk Sector Size / Drive # / Head # as follows:

Bits 0-2: Head Number (0-7)
Bits 3-4: Drive Number (00=#1, 01=#2, 10=#3, 11=#4)
Bits 5-6: Sector Size (00=256, 01=512, 10=1024, 11=128)
Bit 7: Extension (if this is set, Error Checking and Correction codes are in use and the R/W data [sector length + 7 bytes] do not check or generate CRC)

315C

OUT (0CDH),A

OUTPUT the contents of A to Port CDH which is Register 5 for WD1010 Winchester Disk Controller Chip which is the Hard Disk Cylinder LSB.

315E

OUT (0CCH),A

OUTPUT the contents of A to Port CCH which is Register 4 for WD1010 Winchester Disk Controller Chip which is the Hard Disk Cylinder MSB.

3160

LD B,A

LET B = A

3161

DEC B

Decrement B (so now B is 2 lower than the results fro polling Port CBH).

3162

JR Z,3194H

If B is ZERO, JUMP down to 3194H

3164

IN A,(0CFH)

Poll Port CFH and put the result into A.
NOTE: Port CCH is Register 7 for WD1010 Winchester Disk Controller Chip and is the Hard Disk Error Status Register when used for INPut.

3166

AND 40H

MASK the Hard Disk Error against 40H (Binary: 0100 0000) to keep only Bit 6 live. Bit 6 is DRIVE READY.

3168

JR Z,3161H

If the Hard Drive is NOT READY, LOOP back to 3161H.

316AH - If we are here, the Hard Drive returned a READY code and we are going to boot from it.

316A

LD HL,4300H

Let HL = 4300H, which is the standard memory location for loading a BOOT sector into.

316D

LD A,10H

Let A = 10H

316F

CALL 37C2H

GOSUB to 37C2H. Routine will return ZERO FLAG if there is no error.

3172

JR NZ,3194H

If the NOT ZERO flag is set, JUMP forward to 3194H.

3174

LD A,20H

LET A = 20H

3176

CALL 37C2H

GOSUB to 37C2H. Routine will return ZERO FLAG if there is no error.

3179

LD BC,00C8H

Let BC = 00C8H (which sets C to C8H which is the Hard Disk Data Register (Read/Write).

317C

JR Z,3189H

If the ZERO flag is set (from the CALL to 37C2H), skip the next few instructions and go to 3189H

317E

LD A,20H

LET A = 20H (Binary: 0010 0000; meaning only Bit 5 is HIGH)

3180

OUT (0CEH),A

OUTPUT the contents of A to Port CEH (which would be Drive 0, Head 0, 512K Sector).
NOTE: Port CEH is Register 6 for WD1010 Winchester Disk Controller Chip which is the register contaning Hard Disk Sector Size / Drive # / Head # as follows:

Bits 0-2: Head Number (0-7)
Bits 3-4: Drive Number (00=#1, 01=#2, 10=#3, 11=#4)
Bits 5-6: Sector Size (00=256, 01=512, 10=1024, 11=128)
Bit 7: Extension (if this is set, Error Checking and Correction codes are in use and the R/W data [sector length + 7 bytes] do not check or generate CRC)

3182

CALL 37C2H

GOSUB to 37C2H. Routine will return ZERO FLAG if there is no error.

3185

JR NZ,3194H

If the NOT ZERO flag is set, skip the next few instructions and go to 3194H

3187

INIR

3189

INIR

318B

LD HL,43FFH

Let HL = 43FFH

318E

CALL 37B9H

GOSUB to 37B9H

3191

CALL 306FH

GOSUB to 306FH which tests 4400H for FDH and if its there, then JUMP to 4401H, otherwise return here with NZ set.

3194

LD HL,0277H

LET HL = 0277H which is the memory address of the DISKETTE? message.

3197

CALL 309CH

GOSUB back to 309CH (which GOSUBs to 021BH [to display the message pointed to by HL] and then JUMPS to 0049H)

319A

JP 30C3H

JUMP to 30C3H which restarts the system startup (clearing the ports, polling the floppy drives, etc).

319DH - This SUBROUTINE is called by 3543H and 355D.

319D

CALL 3523H

GOSUB to 3523H to test the CPU speed (0 = 2mhz, 1 = 4mhz).

31A0

RET Z

If the Z FLAG is set, RETURN

31A1

RLC (HL)

Rotate the memory contents of (HL) left one bit, copying Bit 7 to BOTH Bit 0 and the CARRY FLAG.

31A3

RET

RETURN

31A4

NOP

31A5H - This SUBROUTINE is called by 3245H and 352CH. it writes 14 .46 volt pulses to tape, 14 .00 volt pulses to tape, waits for 78H loops, and RETURNS.

31A5

LD A,01H

LET Register A = 01H

31A7

OUT (FFH),A

Send 01H to Port FFH.
NOTE: Port FFH is the CASSETTE PORT. Bits 0-2 for OUTPUT control what is written. In the case of 01H a .46 volt spike is written.

31A9

LD B,0DH

LET Register B = 0DH (for a loop of 13).

31AB

DJNZ 31ABH

LOOP back to 31ABH until B is zero (meaning that 14 .46 volt spikes were written).

31AD

LD A,02H

LET Register A = 02H

31AF

OUT (FFH),A

Send 02H to Port FFH.
NOTE: Port FFH is the CASSETTE PORT. Bits 0-2 for OUTPUT control what is written. In the case of 02H a .00 volt spike is written.

31B1

LD B,0DH

LET Register B = 0DH (for a loop of 13).

31B3

DJNZ 31B3H

LOOP back to 31B3H until B is zero (meaning that 14 .00 volt spikes were written).

31B5

CALL 31F3H

GOSUB down to 31F3H.

31B8

LD B,78H

LET Register B = 78H (Decimal: 120)

31BA

DJNZ 31BAH

LOOP back to this same command until B is zero (meaning a delay).

31BC

RET

RETURN

31BDH - This SUBROUTINE resets the cassette, sets the NMI, turns on interrupts, and RETURNs. It is ALSO a VECTOR jump from 400CH.

31BD

LD HL,2CA5H

LET HL = 2CA5H. 2CA5H Points to the "BAD" Message.

31C0

LD A,(4213H)

LET A = the memory contents of 4213H.
NOTE: 4213H holds the Default Interrupt Vector Setting

31C3

OUT (E0H),A

OUTput the value held in Register A to Port E0H which stores the Maskable Interrupt.

31C5

IN A,(FFH)

INput a byte from Port FFH and put it into Register A.
NOTE: Port FFH is the CASSETTE PORT.

31C7

LD A,(4210H)

Put the contents of memory location 4210H into A.
NOTE: 4210H holds the bit mask for port ECH. Port ECH stores miscellaneous controls.

31CA

AND FDH

MASK the memory contents of 4210H against FDH (Binary: 1111 1101) to turn off Bit 1 (which is CASSETTE OFF).

31CC

CALL 31EDH

GOSUB to 31EDH.

31CF

Enable the Interrupts.

31D0

RET

RETURN

31D1 - Turn On The Cassette - Part 1. This will remove the return address, save DE and BC, restore the return address, and than blank the "**"

31D1

EX DE,HL

Swap DE and HL to remove the return address.

31D2

EX (SP),HL

Swap the memory contents pointed to by the STACK POINTER and HL (which is now what DE was).

31D3

PUSH BC

Save BC to the STACK.

31D4

PUSH HL

Save HL to the STACK.

31D5

EX DE,HL

Swap DE and HL back.

31D6

IN A,(ECH)

Poll Port ECH and put the results into A.
NOTE: Port ECH is the Miscellaneous Controls port, which covers clock on/off (Bit 0), cassette motor on or off (Bit 1), double size video on or off (Bit 2), and special character set select of Kana or misc (Bit 3). Higher bits are used for the Model 4 only.

31D8

LD DE," "

Load DE with SPACESPACE.

31DB

LD (3C3EH),DE

Load the screen memory location of 3C3EH with DE.

31DF

CALL 31E8H

GOSUB to 31E8H to turn on the cassette.

31E2

LD BC,7D00H

Load a delay count of 7D00 (Decimal: 32,000) into BC.

31E5

JP 0060H

Jump to 0060H, which JUMPs to the delay routine at 01FBH and RETURNS.

31E8 - Turn On The Cassette - Actually Set the Bit Mask and Output the Command

31E8

LD A,(4210H)

Load A with the memory contents of 4210H.
NOTE: 4210H is the bit mask for Port ECH. Port ECH is the Miscellaneous Controls port, which covers clock on/off (Bit 0), cassette motor on or off (Bit 1), double size video on or off (Bit 2), and special character set select of Kana or misc (Bit 3). Higher bits are used for the Model 4 only.

31EB

OR 02H

OR A with 02H (0000 0010) to set Bit 1.

31ED

LD (4210H),A

Save revised Bit Mask back to 4210H.
NOTE: 4210H is the bit mask for Port ECH. Port ECH is the Miscellaneous Controls port, which covers clock on/off (Bit 0), cassette motor on or off (Bit 1), double size video on or off (Bit 2), and special character set select of Kana or misc (Bit 3). Higher bits are used for the Model 4 only.

31F0

OUT (0ECH),A

Output that Bit Mask to port 0ECH.

31F2

RET

RETURN.

31F3 - Reset the Cassette Port. This routine OUTputs a 0 to the Cassette Port FFH

31F3

XOR A

We want to reset the cassette port so we zero A.

31F4

OUT (0FFH),A

Load Port FFH with A.
NOTE: Port FFH is the cassette port. When outputting to FFH, Bits Zero and 1 set to: 00 is .85V, 01 is .46V, and 10 is 0.0V.

31F6

RET

RETURN.

31F7 - Check to see if we have a PRINT # command and, if so, get the port number, validate that the next character is a , and return.

31F7

LD A,(HL)

Load A with the character pointed to by HL.

31F8

SUB 23H

Subtract 23H so that we can test to see if the caller was a PRINT # command.

31FA

JP NZ,0253H

If that subtraction didn't result in a ZERO (a match), the JUMP to 0253H.
NOTE: 0253H is in the middle of the "Write a Byte to Cassette" Routine. It ends in a RETURN.

31FD

CALL 2B01H

If it was a PRINT # command, then GOSUB to 2B01H to get the device number.

3200

RST 08H
","

So now we have PRINT #n and the next character needs to be a ,, so call RST 08 to check for the next character against a "," and generate a SYNTAX ERROR if it wasn't.

3201

INC L

INCrement Register L

3202

RET

If we are here, then we have PRINT #n, so we RETURN.

3203 - Vector for a SLOW cassette read. Frank saved 2 bytes by putting the memory addresses into BC and then using 1 byte instructions to maipulate the memory address.

3203

LD B,08H

Load B with 8, representing the need to LOOP for 8 bits.

3203

LD B,08H

.. / 0608

3205

CALL 321EH

GOSUB to 321EH.
NOTE: 321EH reads the tape until it finds a timing mark or the BREAK is hit.

3208

DJNZ 3205H

LOOP back to the previous instruction 8 times.

320A

LD BC,4212H

LET BC = 4212H.

320D

LD A,(BC)

Put the contents of the memory location pointed to by (BC) into A.
NOTE: 4212H holds the cassette blinker counter.

320E

INC A

INCrement A

320F

AND 5FH

Mask A against 5F (0101 1111) to turn Bit 7 and Bit 5 off.

3211

LD (BC),A

Put A into (BC).
NOTE: 4212H holds the cassette blinker counter.

3212

JR NZ,321BH

If the masked count is NOT ZERO, then skip the next few instructions.

3214

LD BC,3C3FH

LET BC = 3C3FH (which is a screen address).

3217

LD A,(BC)

Load A with the screen contents held at (BC).

3218

XOR 0AH

XOR A against 0AH (00001010). This turns a "*" into a " " and vice versa as a a "*" is 0010 1010 and when you XOR that against 0000 1010 you get 0010 0000 which is a " " (and vice versa).

321A

LD (BC),A

Put the revised A onto the screen at position 3C3FH.

321B

LD A,D

Put D (the byte) into A.

321C

JR 3296H

JUMP to 3296H to restore the registers and RETURN.

321E - Cassette - Keep reading tape looking for a timing mark or `BREAK`.

321E

PUSH BC

Save BC to the STACK.

321F

IN A,(0FFH)

Poll Port FFH with the results into Register A.
NOTE: FFH is the Cassette Port.

3221

RLA

Put the level received in A into the Carry Bit by rotating A left 1 bit (putting bit 7 into the CARRY FLAG and the old CARRY FLAG into bit 0).

3222

JR C,322CH

If the CARRY FLAG is set then the timing mark was found, so JUMP to 322CH.

3224

CALL 028DH

GOSUB to 028DH to check for a BREAK key.

3227

JR Z,321FH

Loop back to 321FH until we get either a timing mark or a BREAK key.

3229

JP 335AH

If we are here, then we got a BREAK key, so JUMP to 335CH.

322C - Cassette - Wait for the timing mark to pass and the next data to show up. Put that data into Bit 0 of D.

First, wait for 6EH Units (the length of the timing mark)

322C

LD B,6EH

Load B with 6EH, which is the length of the timing mark.

322E

DJNZ 322EH

Loop until B is 0.

Reset the cassette port

3230

CALL 31F3H

GOSUB to 31F3H to RESET the cassette port.

Next, wait for 98H Units (the length until a data pulse is expected)

3233

LD B,98H

Load B with 98H, which is when the next data pulse should be available.

3235

DJNZ 3235H

Loop until B is 0.

... continue

3237

IN A,(FFH)

Poll Port FFH and put the results into A.
NOTE: Port FFH is the Cassette Port.

3239

POP BC

Restore BC from the STACK.

323A

RLA

Rotate A left one bit, with the contents of BIT 7 being put into the CARRY FLAG and the CARRY FLAG are put into BIT 0. This puts the read data into the CARRY FLAG.

323B

RL D

Rotate D left one bit, with the contents of BIT 7 being put into the CARRY FLAG and the CARRY FLAG are put into BIT 0. This puts the read data into BIT 0 of D.

323D

JR 31F3H

JUMP to 31F3H to reset the cassette port and RETURN.

323FH - Vector for a SLOW cassette write. On entry A is the byte to output.

323F

PUSH AF

Save AF to the STACK.

3240

PUSH BC

Save BC to the STACK.

3241

PUSH DE

Save DE to the STACK.

3242

LD C,08H

Load C with an 8, representing 8 bits to be written.

3244

LD D,A

Load D with A.
NOTE: D will be the DATA BYTE.

3245

CALL 31A5H

GOSUB to 31A5H.
NOTE: 31A5H outputs the timing mark.

3248

RLC D

Rotate D left one bit, with the contents of BIT 7 being put into BOTH the CARRY FLAG and BIT 0. This puts the DATA BIT into CARRY.

324A

JR NC,3256H

If there is no DATA BIT (because CARRY is 0) then JUMP to 3256H to wait the appropriate amount of time for a 0 byte to be written.

324C

CALL 31A5H

If we are here, then there was a PULSE, so GOSUB to 31A5H to output the timing bit.

324F

DEC C

Reduce the counter holding the number of bits to deal with by 1.

3250

JR NZ,3245H

Loop back to 3245H until the counter in C hits 0.

3252

POP DE

Restore DE from the STACK.

3253

POP BC

Restore BC from the STACK.

3254

POP AF

Restore AF from the STACK.

3255

RET

RETURN.

3256H - "Write a 0 Bit" by simply waiting the appropriate amount of time and doing nothing.

3256

LD B,9AH

Set a delay of 9A.

3258

DJNZ 3258H

Loop until that hits zero.

325A

JR 324FH

JUMP to 324FH.

325C - SLOW tape header write

325C

PUSH HL

Save HL to the STACK.

325D

LD HL,323FH

Load HL with 323FH.
NOTE: 323FH is the Vector for a SLOW cassette write.

3260

LD (420CH),HL

Load the memory contents of 420CH with HL.
NOTE: 420CH is the TAPE WRITE VECTOR.

3263

LD B,53H

Load B with 53H (Decimal: 83) in prepartion to output 83 ZEROes.

3265

XOR A

Clear A and all flags.

3266

CALL 323FH

GOSUB to 323FH.
NOTE: 3241H is the Vector for a SLOW cassette write.

3269

DJNZ 3266H

Loop back to 3266H until 63 ZEROes have been written.

326B

LD A,0A5H

Load A with A5H.
NOTE: A5H is the OUTPUT SYNC BYTE.

326D

CALL 3241H

GOSUB to 3241H.
NOTE: 3241H is the Vector for a SLOW cassette write.

3270

JR 323FH

JUMP to 323FH to restore all the registers and RETURN.

3272 - SLOW tape header read

3272

PUSH HL

Save HL to the STACK.

3273

LD HL,3203H

Load HL with 3203H.
NOTE: 3203H is the vector for a SLOW cassette read.

3276

LD (420EH),HL

Put the vector for a slow cassette read into the memory location at 420EH.
NOTE: 420EH is the TAPE READ VECTOR.

3279

LD B,40H

Load B with 40H to set up a loop of 64 to try to find 64 zeroes.

327B

LD D,00H

Load D with 0.

327D

CALL 321EH

GOSUB to 321EH.
NOTE: 3220H will keep reading tape looking for a timing mark or BREAK.

3280

LD A,D

Load A with the D (the data byte) to begin to check the current data byte.

3281

OR A

Set up the flags.

3282

JR NZ,3279H

LOOP back to 3279H until A is ZERO.

3284

DJNZ 327DH

Loop back to 327DH 64 times.

3286

CALL 321EH

GOSUB to 321EH.
NOTE: 3220H reads the tape until it finds a timing mark or the BREAK is hit.

3289

LD A,D

Load A with the D (the data byte) to begin to check the current data byte.

328A

CP 0A5H

Compare A to A5H looking for a SYNC BYTE.

328C

JR NZ,3286H

JUMP back to to 3286H if a SYNC BYTE wasn't found.

329E

LD HL,"**"

In preparation to display a "**", load HL with **.

3291

LD (3C3EH),HL

Put HL onto the screen at location 3C3EH.

3294

LD A,H

Load A with H (which is a *.

3295

POP HL

Restore HL from the STACK.

3296

POP BC

Restore BC from the STACK.

3297

POP DE

Restore DE from the STACK.

3298

RET

RETURN.

3299 - FAST tape header write.

3299

PUSH HL

Save HL to the STACK.

329A

LD HL,32B8H

Load HL with 32B8H.
NOTE: 32B8H is the VECTOR TO FAST WRITE.

329D

LD (420CH),HL

Load the memory contents of 420CH with HL.
NOTE: 420CH is the TAPE WRITE VECTOR.

32A0

LD B,00H

Load B with 00H to set up a loop of 256 to output 256 "55H" bytes.

32A2

LD A,55H

Load A with "55H".

32A4

CALL 32B2H

GOSUB to 32B2H.
NOTE: 32B4 restore all registers from the STACK, and Fill C with A, and JUMP to cassette write

32A7

DJNZ 32A2H

LOOP back to 32A2H 256 times.

32A9

LD A,7FH

Load A with 7FH.
NOTE: 7FH is the OUTPUT SYNC BYTE.

32AB

CALL 32B2H

GOSUB to 32B2H.
NOTE: 32B4 restore all registers from the STACK, and Fill C with A, and JUMP to cassette write

32AE

LD A,A5H

Load A with A5H.
NOTE: A5H is the SLOW SYNC BYTE.

32B0

JR 3295H

JUMP to 3295H to restore all the registers and RETURN.

32B2 - Restore all registers from the STACK, and Fill C with A, and JUMP to cassette write.

32B2

PUSH AF

Save AF to the STACK.

32B3

PUSH BC

Save BC to the STACK.

32B4

PUSH DE

Save DE to the STACK.

32B5

LD C,A

Load C with A.

32B6

JR 32BFH

JUMP to 32BFH.
NOTE: 32C1H will write to cassette without a start bit.

32B8 - Save all registers to the STACK, and Fill C with A, GOSBUB to write out the START BIT ...

32B8

PUSH AF

Save AF to the STACK.

32B9

PUSH BC

Save BC to the STACK.

32BA

PUSH DE

Save DE to the STACK.

32BB

LD C,A

Load C with A.

32BC

CALL 333CH

GOSUB to 333CH to write the START BIT.

32BF - Call 3335H to Output a Bit 8 Times

32BF

LD B,08H

Load B with an 8 to set up a loop for 8 bits.

32C1

CALL 3333H

GOSUB to 3333H to output the bit.

32C4

DJNZ 32C1H

Loop back one instruction for all 8 bits.

32C6

JR 3252H

JUMP to 3252H to restore all the registers and RETURN.

32CAH - Read the start bit, read 8 bits, check for error, and flash the star

32C8

CALL 334EH

GOSUB to 334EH to READ START BIT.

32CB

LD B,08H

Load B with an 8 to set up a loop for 8 bits.

32CD

CALL 334EH

GOSUB to 334EH to READ BIT.

32D0

CALL 337AH

GOSUB to 337AH to CHECK FOR DATA ERROR.

32D3

DJNZ 32CDH

Loop back 2 instructions for all 8 bits.

32D5

JP 320AH

JUMP to 320AH to flash the *.

32D8H - FAST tape header read.

32D8

PUSH HL

Save HL to the STACK.

32D9

LD HL,32C8H

Load HL with 32C8H.
NOTE: 32C8H reads an verifies a byte.

32DC

LD (420EH),HL

Load the TAPE READ VECTOR (memory location of 420EH) with the 32CAH.

32DF

LD A,01H

Load A with a 1 to set the interrupt.

32E1

OUT (E0H),A

OUTPUT A to Port E0H which is the maskable interrupt latch, which directs jumps.
Jump Table:

xxxxxxx1 jumps to 3365H
xxxxxx1x jumps to 3369H
xxxxx1xx jumps to 4046H
xxxx1xxx jumps to 403DH
xxx1xxxx jumps to 4206H
xx1xxxxx jumps to 4209H
x1xxxxxx jumps to 44040H
1xxxxxxx jumps to 44043H

32E3

LD B,80H

Set up a loop of 80H (128) to try to read 128 bits.

32E5

CALL 334EH

GOSUB to 334EH to READ a BIT.

32E8

LD A,C

Load A with C (which is the pulse width).

32E9

CP 0FH

Compare A to 0FH to see if the pulse width was too short.

32EB

JR C,32E3H

Loop back to 32E3H if the pulse width was too short.

32ED

CP 3EH

Compare A to 3EH to see if the pulse width was too long.

32EF

JR NC,32E3H

Loop back to 32E3H if the pulse width was too long.

32F1

DJNZ 32E5H

Loop back to 32E5H 128 times.

32F3

LD HL,0000H

Load HL with 0000.

32F6

LD B,40H

Set up a loop of 40H (Decimal: 64) to try to read 64 bits.

32F8

CALL 334EH

GOSUB to 334EH to READ BIT.

32FB

CALL 334EH

GOSUB to 334EH to READ BIT.

32FE

LD D,C

Load D with C (which holds the delay count).

32FF

CALL 334EH

GOSUB to 334EH to READ BIT.

3302

LD A,D

Load A with D to set up to find the difference in the delays.

3303

SUB C

Subtract C (the delay count) from A (which holds D).

3304

JR NC,3308H

JUMP to 3308H (to GET ABSOLUTE) if the carry flag is NOT set.

3306

NEG

A = 0 - A.

3308

CP 0DH

Compare the NEGated A against 0DH. This has the effect of checking A-0DH, so if A < 0DH then the CARRY will be set and if A >= 0DH then the NO CARRY will be set.

330A

JR C,3311H

If the CARRY FLAG is set, JUMP to 3311H which will bump L and continue the 64 bit loop.

330C

INC H

Bump HL since we have one more zero bit.

330D

DJNZ 32F8H

Loop back to 32F8H until 64 bits read.

330F

JR 3314H

JUMP out of the loop to 3314H.

Routine continuation ... jumped from 330A

3311

INC L

Bump L since we have one more bit.

3312

DJNZ 32F8H

Loop back to 32F8H until 64 bits read.

3314

LD A,40H

Load A with 40H (64).

3316

CP H

Compare A with H to check for bits.

3317

JR Z,3323H

If they match, then JUMP forward to 3323H.

3319

CP L

Compare with A to check for one bits.

331A

JR NZ,32F3H

If not, JUMP forward to 32F3H.

331C

LD A,02H

Load A with 2 to set the interrupt vector.

332E

OUT (E0H),A

Output the 2 to Port E0H which is the maskable interrupt latch, which directs jumps.
Jump Table:

xxxxxxx1 jumps to 3365H
xxxxxx1x jumps to 3369H
xxxxx1xx jumps to 4046H
xxxx1xxx jumps to 403DH
xxx1xxxx jumps to 4206H
xx1xxxxx jumps to 4209H
x1xxxxxx jumps to 44040H
1xxxxxxx jumps to 44043H

3320

CALL 334EH

GOSUB to 334EH to READ BIT.

3323

LD D,00H

Zero D.

3325

CALL 334EH

GOSUB to 334EH to READ BIT.

3328

CALL 337AH

GOSUB to 337AH to check for a data error.

332B

LD A,D

Load A with D (the read byte).

332C

CP 7FH

Compare A against 7F to check for a MARKER BYTE.

333E

JR NZ,3325H

If no marker byte, then JUMP to 3325H.

3330

JP 328EH

If it was a marker byte, then JP to 328EH to flash the * and continue.

3333

RLC C

We need to shift the bit into CARRY so we rotate C left one bit, copying BIT 7 to the CARRY FLAG and the CARRY FLAG to BIT 0.

3335

JR NC,333CH

If the bit was 0, JUMP forward 2 instructions to 333CH.

3337

LD DE,1217H

Load DE with 1217H to set up a delay for 1 BIT.

333A

JR 333FH

Skip the next instruction.

333C

LD DE,2B2FH

Load DE with 2B2F to set the delay for a 0 BIT.

333F

DEC D

Decrement D as DELAY #1.

3340

JR NZ,333FH

JUMP back to the prior instruction until D is 0.

3342

LD A,02H

Load A with a 2 to set up for a write of 0 VOLTS to TAPE.

3344

OUT (FFH),A

Load Port FFH with A.
NOTE: Port FFH is the cassette port. When outputting to FFH, Bits Zero and 1 set to: 00 is .85V, 01 is .46V, and 10 is 0.0V.

3346

DEC E

Decrement E as DELAY #2.

3347

JR NZ,3346H

JUMP back to the prior instruction until E is 0.

3349

LD A,01H

Load A with 01H to prepare to send 0.85 VOLTS to TAPE.

334B

OUT (FFH),A

Load Port FFH with A.
NOTE: Port FFH is the cassette port. When outputting to FFH, Bits Zero and 1 set to: 00 is .85V, 01 is .46V, and 10 is 0.0V.

334D

RET

RETURN.

334EH - READ a BIT

334E

Enable Interrupts.

334F

LD C,00H

Load C with 0.

3351

INC C

Bump C.

3352

LD A,(3840H)

Load A with the contents of 3840H so as to check for a BREAK.

3355

AND 04H

Mask A with 4 (0000 0100).

3357

JR Z,3351H

If the Masked A is 0, then LOOP back to 3351H.

3359

Disable Interrupts.

335A

LD HL,4B42H

Load HL with "BK" to set up to display "BK" over the "**".

335D

LD (3C3EH),HL

Put the "BK" in HL onto the video screen at 3C3EH.

3360

JP 4203H

JUMP to 4203H, which then jumps to 022EH, which is the BREAK VECTOR for cassette and RS-232.

3363 - This is a Port E0H Masked Jump. If the MASKABLE INTERRUPT is xxxxxxx1, it jumps here.

3363

LD E,01H

Load E with 01H (Binary: 0000 0001) to make the bit go high.

3365

JR 3369H

Skip the next instruction.

3367

LD E,00H

Load E with 0 to make the bit go low.

3369

LD A,06H

Load A with 6.

336B

ADD A,C

Add A (6) to C, so COUNT = COUNT + 6.

336C

LD C,A

Put the count held in A back into C.

336D

IN A,(FFH)

Poll FFH (to get the level) into A.
NOTE: FFH is the Cassette Port.

336F

AND 01H

Mask A with 1 (0000 0001) to keep only Bit 0.

3371

CP E

Compare A with E (which was the set level).

3372

JR NZ,3377H

If A does NOT match E then skip the next 3 instructions.

3374

POP AF

Restore AF from the STACK.

3375

POP AF

Restore AF (the REMOTE CALLER'S ADDRESS) from the STACK.

3376

RET

RETURN to the caller's caller.

3377

POP AF

Restore AF from the STACK.

3378

Enable Interrupts.

3379

RET

RETURN back top the loop.

337AH - Check for a Data Error.

337A

LD A,C

Load A with C (the count).

337B

CP 22H

Compare A with 22H. Results:

If A=22H it sets the ZERO FLAG
If A<22H then the CARRY FLAG will be set
If A>=22H then the NO CARRY FLAG will be set

337D

RL D

We need to put the data bit into D so we rotate D left one bit, with the contents of BIT 7 being put into the CARRY FLAG and the CARRY FLAG are put into BIT 0. This puts the read data into BIT 0 of D.

337F

CP 0FH

Make sure it was not too quick by checking A against 0FH. This has the effect of checking A-0FH, so if A < 0FH then the CARRY will be set and if A >= 0FH then the NO CARRY will be set.

3381

JR C,3386H

If A < 0FH then it was too quick and we have a data error so JUMP forward a few instructions 3386H.

3383

CP 3EH

Compare A against 3EH to make sure it was not too slow.

3385

RET C

If it wasn't too slow, RETURN.

3387

LD A,44H

It was too slow, so load A with a D.

3388

LD (3C3EH),A

Put the "D" on the screen at video location 3C3EH.

338B

RET

RETURN.

338CH - Keyboard Routine - VECTORed from 3024H.

338C

LD HL,4036H

Load HL with 4036H (BUFFER ROW 0).

338F

LD BC,3801H

Load BC with 3801H (KEYBOARD ROW 0).

3392

LD D,00H

Load D with 0 (so D = ROW 0).

3394

LD A,(BC)

Load A with the contents held in (BC) to check the keyboard row.

3395

LD E,A

Load E with the contents held in (BC) to check the keyboard row.

3396

XOR (HL)

XOR (HL) to set changed bits.

3397

JR NZ,33C5H

JUMP to 33F8H if the XOR resulted in ZERO.

3399

INC D

Bump D so that D holds the NEXT row number.

339A

INC HL

Bump HL so that HL holds the NEXT buffer location.

339B

RLC C

We need C to point to the next row of keys, so we rotate C left one bit, copying BIT 7 to the CARRY FLAG and the CARRY FLAG to BIT 0.

339D

JP P,3394H

If the PARITY BIT is set, Jump to back to 3394H

33A0

LD HL,41F4H

LET HL = 41F4H.

33A3

LD A,(BC)

Put the contents of the memory location pointed at by (BC) into Register A.

33A4

AND 78H

Mask those memory contents against 78H (Binary: 1111000) to remove the lowest 3 bits.

33A6

LD E,A

LET Register E = the MASKed version of A.

33A7

XOR (HL)

XOR (HL) to set changed bits.

33A8

JR NZ,33C5H

If the XOR resulted in a NOT ZERO flag, JUMP to the next routine below at 33C5H.

33AA

LD A,(41FDH)

Load A with the memory contents of 41FDH.
NOTE: 41FDH is the saved position in the keyboard scan.

33AD

INC A

Increment A

33AE

RET Z

If the INCrement turned A to Zero (meaning 41DFH held FFH) then RETURN

33AF

LD HL,(4201H)

Load HL with the repeat delay counter.
NOTE: 4201H is the REPEAT DELAY COUNTER.

33B2

DEC HL

Decrement HL

33B3

LD (4201H),HL

Load the memory location at 4201H with the decremented HL to lessen the repeat counter.
NOTE: 4201H is the REPEAT DELAY COUNTER.

33B6

LD A,H
OR L

Test for HL=0. If you LD A,H and OR L, Z will be set only if H and L were zero.

33B8

JR NZ,3402H

If HL was NOT zero, JUMP forward to 3402H

33BA

LD A,(41FEH)

Load A with the memory contents of 41FEH.
NOTE: 41FEH is the saved IMAGE at the saved position in the keyboard scan data.

33BD

LD (4201H),A

Put the value from (41FEH) into (4201H).
NOTE: 4201H is the REPEAT DELAY COUNTER.

33C0

LD A,(4018H)

Load A with the memory contents of 4018H.
NOTE: 4018H is the Right Shift Toggle in the keyboard device contol block.

33C3

CP L

Compare Register A with Register L. Results:

If A=L it sets the ZERO FLAG
If A<L then the CARRY FLAG will be set
if A>=L then the NO CARRY FLAG will be set.

33C4

RET

RETURN

33C5H - Inside Keyboard Routine - JUMPed to from the XOR commands above

33C5

PUSH AF

Store Register Pair AF to the STACK

33C6

PUSH BC

Store Register Pair BC to the STACK

33C7

LD BC,0152H

LET BC = 0152H

33CA

CALL 3523H

GOSUB to 3523H to test the CPU speed (0 = 2mhz, 1 = 4mhz).

33CD

JR Z,33D2H

If the ZERO FLAG is set, skip the next instruction

33CF

LD BC,02A4H

LET BC = 02A4H, because we are in 4mhz speed and we need a higher delay

33D2

CALL 0060H

GOSUB to 0060H which jumps to the delay routine at 01FBH (which uses BC as a loop counter). It RETs when done so it doesn't come back here.

33D5

POP BC

Restore Register Pair BC from the STACK

33D6

LD A,(BC)

LET Register A = the memory contents held at (BC), which is either 0152H or 02A4H

33D7

CP E

Compare A with E.

33D8

POP BC

Restore Register Pair BC from the STACK (used to be AF)

33D9

JR NZ,3402H

If Register A does NOT equal Register E then JUMP to 3402H

33DB

LD A,B

LET Register A = Register B

33DC

AND E

MASK Register A with Register E to set a pattern

33DD

LD E,A

LET E = the masked Register A.

33DE

JR NZ,33E2H

If the MASK returned a NOT ZERO flag, then JUMP forward a few instructions to 33E2H

33E0

LD E,B

LET Register E = Register B

33E1

LD B,A

LET Register B = Register A

33E2

LD A,D

Let Register A = Register D

33E3

RLCA

Rotate the contents of Register A LEFT one bit. Bit 7 is copied both to the CARRY FLAG and to Bit 0

33E4

RLCA

Rotate the contents of Register A LEFT one bit. Bit 7 is copied both to the CARRY FLAG and to Bit 0

33E5

RLCA

Rotate the contents of Register A LEFT one bit. Bit 7 is copied both to the CARRY FLAG and to Bit 0

33E6

LD D,A

LET Register D = the rotated Register A.

33E7

LD C,01H

LET Register C = 01H

33E9

LD A,C

LET Register A = Register C

33EA

AND E

MASK Register A with Register E to set a pattern

33EB

JR NZ,33F2H

If the MASKed Register A is NOT ZERO, then JUMP to 33F2H

33ED

INC D

If the MASKed Register A is ZERO, Bump D so that D holds the NEXT row number.

33EE

RLC C

We need C to point to the next row of keys, so we rotate C left one bit, copying BIT 7 to the CARRY FLAG and the CARRY FLAG to BIT 0.

33F0

JR 33E9H

JUMP back to 33E9H to keep testing and bumping keyboard rows.

33F2 - Inside Keyboard Routine

33F2

LD A,C

LET Register A = Register C

33F3

XOR (HL)

Invert the contents of the memory location pointed to by (HL).

33F4

LD (HL),A

Put the contents of Register A into the memory location pointed to by (HL)

33F5

LD A,B

LET Register A = Register B.

33F6

OR A

OR Register B against Register A to set the flags.

33F7

JR NZ,3404H

If the NOT ZERO flag is set, JUMP down to 3404H

33F9

LD HL,41FDH

Let HL = 41FDH

33FC

LD A,(HL)

Load Register A with the memory contents pointed to by Register Pair HL.

33FD

CP D

Compare the memory contents pointed to by Register Pair HL with the value held in Register D

33FE

JR NZ,3402H

if the memory contents pointed to by Register Pair HL are not the same as the value held in Register D, skip the next instruction.

3400

LD (HL),FFH

Put a FFH into the memory location pointed to by Register pair HL

3402

XOR A

Clear A and all flags.

3403

RET

RETURN.

3404 - Inside Keyboard Routine

3404

LD HL,4019H

Load HL with 4019H.
NOTE: 4019H holds the caps lock toggle in the keyboard DCB.

3407

LD A,(HL)

Load Register A with the caps lock toggle (held at the memory location pointed to by Register Pair HL.)

3408

AND 51H

MASK the CAPS LOCK TOGGLE with 51H (Binary: 0101 0001)

340A

LD B,A

LET Register Pair B = Register Pair A to save A.

340B

LD A,(3880H)

Load A with the memory contents of (3880H) (which are the SHIFT KEYS).

340E

BIT 2,A

Check Bit 2 of Register A.

3410

JR NZ,3425H

If Bit 2 of Register A is HIGH, JUMP down to 3425.

3412

AND 03H

MASK Register A with 03H (Binary: 0000 0011) to keep only Bits 0 and 1 to check for shifts.

3414

JR Z,3427H

If the MASKed Register A is ZERO (meaning no SHIFT keys), JUMP to 3427H

3416

SET 1,B

SET Bit 1 of Register B (it was MASKed off in 3408H)

3418

BIT 6,B

TEST Bit 6 of Register B (it was RETAINED in the MASK)

341A

JR NZ,3427H

It Bit 6 of Register B is LOW, JUMP to 3427H

341C

LD A,(3840H)

Load A with the contents of 3840H.
NOTE: 3840H holds ENTER (1), CLEAR (2), BREAK (4), Right Arrow (8), Line Feed (16), Left Arrow (32), and SPACE (64).

341F

AND 10H

MASK Register A against 10H (Decimal: 16) to check for LINE FEED

3421

JR Z,3427H

If we have a LINE FEED, JUMP to 3427H.

3423

SET 5,B

SET Bit 5 of Register B.

3425

SET 7,B

SET Bit 7 of Register B.

3427

LD A,D

LET Register A = Register D.

3428

CP 1BH

Check Register A (which was Register D) against 1BH (Binary: 0001 1011).

342A

JR NC,3446H

If Register A (which was Register D) does NOT equal 1BH, JUMP to 3446H

342C

BIT 7,B

Test Bit 7 of Register B.

342E

JR NZ,3478H

If Bit 7 of Register B is NOT zero, then JUMP to 3478H

3430

ADD A,40H

ADD 40H (Decimal: 64; or 1 character below "A") to Register A to make Register A an ASCII value.

3432

LD C,A

LET Register C = Register A.

3433

CP 40H

Compare Register C against against 40H (Binary: 0100 0000, Decimal: 64)

3435

JR Z,3440H

If Register C = 40H tjhen JUMP down to 3440H.

3437

LD A,B

LET Register A = Register B.

3438

AND 03H

MASK Register A with 03H (Binary: 0000 0011)

343A

JR NZ,3477H

If the lowst 2 bits of Register B were not 00, JUMP to 3477H.

343C

SET 5,C

SET Bit 5 of Register C.

343E

JR 3477H

JUMP to 3477H

3440 - Inside Keyboard Routine

3440

BIT 1,B

Test Bit 1 of Register B.

3442

JR NZ,343CH

If Bit 1 of Register B is HIGH, Jump to 343CH

3444

JR 3478H

If Bit 1 of Register B is LOW, Jump to 3478H

3446 - Inside Keyboard Routine

3446

CP 3BH

Compare Register A with 3BH.

3448

JR Z,3462H

If Register A is not 3BH, then JUMP to 3462H.

344A

CP 30H

Compare Register A with 30H (ASCII: 0). Results:

If A=30H it sets the ZERO FLAG
If A<30H then the CARRY FLAG will be set
if A>=30H then the NO CARRY FLAG will be set.

344C

JR NC,348DH

If Register A is at least a "0" or higher, JUMP to 348DH

344E

BIT 7,B

If we are here then Register A is less than 30H, so test Bit 7 of Register B.

3450

JR NZ,346CH

if Register A is less than 30H and Bit 7 of Register B is HIGH, them JUMP to 346CH

3452

ADD A,10H

LET Register A = Register A + 10H.

3454

CP 3CH

Compare Register A with 3CH (ASCII: <). Results:

If A=3CH it sets the ZERO FLAG
If A<3CH then the CARRY FLAG will be set
if A>=3CH then the NO CARRY FLAG will be set.

3456

BIT 1,B

Test Bit 1 or Register B. This command does NOT affect the C FLAG so any test for the C FLAG is still based on the prior instruction.

3458

JR NC,3468H

If Register A>=3CH then JUMP to 3468H

345A

JR Z,3478H

If Bit 1 of Register B is ZERO, themn JUMP to 3478H

345C

XOR 10H

XOR Register A against 10H (Binary: 0001 0000) to toggle Bit 4 of Register A

345E

CP 20H

Check the XOR'd Register A against 20H (ASCII: SPACE)

3460

JR NZ,3478H

If the XOR'd Register A then JUMP to 3478H

3462

LD A,01H

LET Register A = 01H

3464

XOR (HL)

Toggle the value in Register A against the value held in the memory location pointed to by Register Pair HL.

3465

LD (HL),A

Put the contents of Register A into the memory location pointed to by (HL)

3466

XOR A

Clear A and all flags.

3467

RET

RETURN.

3468 - Inside Keyboard Routine

3468

JR NZ,3478H

If the NZ FLAG is set, then JUMP to 3478H

346A

JR 345CH

If the Z FLAG is set, JUMP to 345CH

346C - Inside Keyboard Routine

346C

LD HL,34B2H

LET Register Pair HL = 34B2H

346F

ADD A,L

LET Register A = Register A + Register L

3470

LD L,A

LET Register L = Register A.

3471

LD C,(HL)

LET Register C = the contents of the memory location pointed to by Register Pair HL.

3472

LD A,C

LET Register A = Register C.

3473

INC A

INCrement Register A by 1.

3474

JP Z,3781H

If Register A is ZERO (meaning Register C was FFH) then JUMP to 3781H

3477

LD A,C

LET Register A = Register C.

3478

LD HL,(41FFH)

LET Register Pair HL = the memory contents held at 41FFH.
NOTE: 41FFH holds the Keyboard Scan Repeat Delay Count

347B

LD (4201H),HL

Put the Keyboard Scan Repeat Delay Count (held in Register Pair HL) into 4201H.
NOTE: 4201H holds the Keyboard Scan Repeat Delay Counter

347E

LD (4018H),A

Put Register A into 4018H which holds the flag for the Right Shift Toggle

3481

LD HL,41FDH

Let Register Pair HL = 41FDH

3484

LD (HL),D

Put Register D into the contents of the memory location pointed to by Register Pair HL.

3485

CP 01H

Compare Register A against 01H (Binary: 0000 0001).

3487

RET NZ

If Register A did NOT equal 01H, then RETURN

3488

BIT 4,B

If Register A=01H, then Test Bit 4 of Register B.

348A

RET NZ

If Register A=01H and Bit 4 of Register B=1, RETURN

348B

RST 28H

If Register A=01H and Bit 4 of Register B=0, call RST 28H to handle the BREAK.

348C

RET

RETURN.

348D - Inside Keyboard Routine

348D

CP '8'

Compare Register A with "8". Results:

If A="8" it sets the ZERO FLAG
If A<"8" then the CARRY FLAG will be set
if A>="8" then the NO CARRY FLAG will be set.

348F

JR NC,34C1H

If Register A>="8" then JUMP to 34C1H.
NOTE: "8" is the first character on the 3820H keyboard row.

3491

CP '3'

Compare Register A with "3". Results:

If A="3" it sets the ZERO FLAG
If A<"3" then the CARRY FLAG will be set
if A>="3" then the NO CARRY FLAG will be set.

3493

JR C,346CH

If Register A<"3" then JUMP to 346CH

3495

CP '7'

Compare Register A with "7". Results:

If A="7" it sets the ZERO FLAG
If A<"7" then the CARRY FLAG will be set
if A>="7" then the NO CARRY FLAG will be set.

3497

LD C,' '

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

3499

JR Z,3477H

If Register A = "7", then JUMP to 3477H

349B

CP '3'

Compare Register A with "3". Results:

If A="3" it sets the ZERO FLAG
If A<"3" then the CARRY FLAG will be set
if A>="3" then the NO CARRY FLAG will be set.

349D

JR NZ,34AAH

If Register A does NOT EQUAL "3" then JUMP to 34AAH

349F

LD C,5BH

LET Register C = 5BH (ASCII: [)

34A1

LD A,B

LET Register A = Register B.

34A2

AND 82H

MASK Register A against 82H (Binary: 1000 0010) to keep only Bits 1 and 7.

34A4

JR Z,3477H

If Bits 1 and 7 of Register A are both 0, JUMP to 3477H

34A6

LD A,1BH

LET Register A = 1BH.

34A8

JR 3478H

JUMP to 3478H

34AA - Inside Keyboard Routine

34AA

CP "4"

Compare Register A with "4". Results:

If A="4" it sets the ZERO FLAG
If A<"4" then the CARRY FLAG will be set
if A>="4" then the NO CARRY FLAG will be set.

34AC

JR NZ,34B6H

If Register A does NOT EQUAL "4" then JUMP to 34B6H

34AE

BIT 5,B

Test Bit 5 of Register B

34B0

JR NZ,3466H

If Bit 5 of Register B is 1, then JUMP to 3466H

34B2

LD A,0AH

LET Register A = 0AH.

34B4

JR 3478H

JUMP to 3478H

34B6 - Inside Keyboard Routine

34B6

LD C,09H

LET Register C = 09H

34B8

CP "6"

Compare Register A with "6". Results:

If A="6" it sets the ZERO FLAG
If A<"6" then the CARRY FLAG will be set
if A>="6" then the NO CARRY FLAG will be set.

34BA

JR Z,34BDH

IF Register C = "6" then JUMP to 34BDH

34BC

DEC C

DECrement Register C.

34BD

LD A,C

LET Register A = Register C.

34BE

SCF

Set the CARRY FLAG.

34BF

JR 3456H

JUMP to 3456H

34C1 - Inside Keyboard Routine

34C1

CP "<"

Compare Register A with "<". Results:

If A="lt;" it sets the ZERO FLAG
If A<"lt;" then the CARRY FLAG will be set
if A>="lt;" then the NO CARRY FLAG will be set.

34C3

JR C,3466H

IF Register A<"lt;" then JUMP to 3466H

34C5

SUB 6DH

SUBtract 6DH from Register A.

34C7

LD L,A

LET Register L = Register A.

34C8

LD H,34H

LET Register H = 34H.

34CA

LD L,(HL)

LET Register L = the value stored at the memory location pointed to by Register Pair HL.

34CB

LD H,41H

LET Register H = 41H.

34CD

JR 3471H

JUMP to 3471H

34CFH - Inside Keyboard Routine - I'm not convinced that the code here did anything.

34CF

EX DE,HL

Exchange the value held in Register Pair DE with the value held in Register Pair HL.

34D0

CALL PE,7CF3H

If the PARITY EVEN FLAG is set, JUMP to 7CF3H

34D3

DEC DE

DECrement Register Pair DE by 1.

34D4

INC E

INCrement Register E by 1.

34D5

DEC E

DECrement Register E by 1.

34D6

LD E,7FH

LET Register E = 7FH.

34D8

LD A,(HL)

Load Register A with the memory contents pointed to by Register Pair HL.

34D9

LD H,B

LET Register H = Register B.

34DA

LD A,E

LET Register A = Register E.

34DB

LD A,L

LET Register A = Register L.

34DC

RST 38H

. / FF

34DD

LD E,(HL)

. / 5E

34DE

LD E,E

. / 5B

34DF

LD E,A

. / 5F

34E0

LD E,L

. / 5D

34E1

LD E,H

. / 5C

34E2

DEC C

DECrement Register C.

34E3

RRA

Rotate the contents of A one bit to the right, with the contents of the carry bit being moved to bit 7 and the contents of bit 0 being moved to the carry bit. If Bit 0 is low then NC will be set.

34E4

LD BC,3EC1H

LET Register Pair BC = 3EC1H

34E5 - Network 4 BOOT Routine - Jumped here if the keypress was not a 3.

34E5

POP BC

Restore the STACK to BC.

34E6

LD A,0EEH

Let Register A = EEH (Binary: 1110 1110).

34E8

OUT (0E9H),A

Output A to Port E9H.
NOTE: Port E9H is the RS-232 Baud Rate Selects and Sense Switches. Outputting to Port E9H will set the Baud Rate as follows:

Bits 0-3 - Select the Receive Rate
Bits 4-7 - Select the Transmit Rate

34EA

IN A,(E8H)

Poll Port E8H and put the result into A.
NOTE: Port E8H is the RS-232 Status Register & Master Reset. Input:

Bit 4: Ring Indicator
Bit 5: Carrier Detect
Bit 6: Data Set Ready
Bit 7: Clear to Send

34EC

BIT 6,A

Test Bit 6 of Port E8H. Bit 6 is DATA SET READY.

34EE

JR Z,34EAH

If Bit 6 of Port E8H is 0, JUMP back to the prior instruction.

34F0

LD A,6CH

LET Register A = 6CH (Binary: 0110 1100). When applied to port EAH this means: Data Terminal Ready, Ready to Send, Send BREAK signal, Parity: Disabled, Stop Bits: 0, Word Length: 7, Parity: Odd

34F2

OUT (0EAH),A

Output the configuration code held in Register A to Port EAH.
NOTE: Port EAH is the RS-232 UART Control Register/Status Register. For output:

Bit 0: Data Terminal Ready
Bit 1: Request to End
Bit 2: Break
Bit 3: Parity Enable
Bit 4: Stop Bits
Bit 5: Select
Bit 6: Word Length
Bit 7: Parity (0=Odd, 1=Even)

34F4

IN A,(E8H)

Poll Port E8H and put the result into A.
NOTE: Port E8H is the RS-232 Status Register & Master Reset. Input:

Bit 4: Ring Indicator
Bit 5: Carrier Detect
Bit 6: Data Set Ready
Bit 7: Clear to Send

34F6

BIT 6,A

Test Bit 6 of Port E8H. Bit 6 is DATA SET READY.

34F8

JR NZ,34F4H

If Bit 6 of Port E8H is NOT ZERO, LOOP back 2 instructions to 34F4H.

34FA

LD A,0FH

LET Register A = 0FH.

34FC

OUT (0EBH),A

Send A out of Port EBH which is the RS-232C Data Register. It contains the data to be sent to the RS-232C.

34FE

CALL 3670H

GOSUB to 3670H

3501

CALL 3670H

GOSUB to 3670H

3504

OUT (0EBH),A

Send A out of Port EBH which is the RS-232C Data Register. It contains the data to be sent to the RS-232C.

3506

OR A

Set the FLAGS for Register A

3507

JR NZ,34E5H

IF Register A is NOT ZERO, then LOOP back to the top of this routine at 34E5H

3509

LD HL,4300H

LET Register Pair HL = 4300H.
NOTE: 4300H is the traditional memory location for a DOS boot.

350C

CALL 3670H

GOSUB to 3670H

350F

LD (HL),A

Put the contents of Register A into the memory location pointed to by (HL)

3510

INC L

INCrement Register L by 1.

3511

JR NZ,350CH

If the contents of the memory location pointed to by (HL) are NOT ZERO, JUMP to 350CH.

3513

LD A,6FH

LET Register A = 6FH (Binary: 0110 1111).

3515

OUT (EAH),A

Output the configuration code held in Register A to Port EAH.
NOTE: Port EAH is the RS-232 UART Control Register/Status Register. For output:

Bit 0: Data Terminal Ready
Bit 1: Request to End
Bit 2: Break
Bit 3: Parity Enable
Bit 4: Stop Bits
Bit 5: Select
Bit 6: Word Length
Bit 7: Parity (0=Odd, 1=Even)

3517

JP (HL)

JUMP to the memory address pointed to by the memory location pointed to by Register Pair (HL).

3518 - This SUBROUTINE is called during WARM BOOT. It handles setting up the Port 84H Settings (as explained in this section).

3518

LD A,80H

LET Register A = 80H (Binary: 1000 0000; Bit 7 High).

351A

CALL 351EH

GOSUB to 351EH to send a byte to Port 84H, which will set the VIDEO PAGE SELECT to PAGE 1.

351D

XOR A

Clear A and all flags.

351E

OUT (84H),A

OUTput Register A to Port 84H, which will have the effect of saying: Model III ROMs Enabled, Video/Keyboard are Model III, Video Mode 64x16, Lower 32K RAM in Bank 0 and Upper 32K RAM in Bank 1, and Video Page Select 0.
NOTE: Port 84H handles miscellaneous memory items. Output:

Bits 0-1: Identify the Model of the Computer
Bit 2: Video Display Mode [0=64x16, 1=80x24]
Bit 3: Reverse Video
Bit 4-6: RAM Bank Select
Bit 7: Video Page Select [0=Page 0, 1=Page 1]

3520

JP 01C9H

JUMP to the Clear the Screen routine.

3523H - This SUBROUTINE tests the active CPU SPEED and sets Z accordingly (Z=2mhz, NZ=4mhz)

3523

LD A,(4210H)

Put the contents of memory location 4210H into A.
NOTE: 4210H holds the bit mask for port ECH. Port ECH stores miscellaneous controls.

3526

AND 40H

MASK Register A against 40H (Binary: 0100 0000) to leave only Bit 6 live. Bit 6 would be the CPU CLOCK SPEED (0=2mhz, 1=4mhz)

3528

RET

RETURN.

3529 - Deal with the cursor.

3529

LD DE,3593H

LET Register Pair DE = 3593H

352C

PUSH DE

Save the contents of Register Pair DE to the STACK

352D

IN A,(0ECH)

352F

LD A,(4022H)

Check to see if the Cursor is on by loading (4022H) into A.
NOTE: 4022H holds the Cursor ON/OFF Flag and will be 0 if the cursor is off, or the underscore character otherwise.

3532

OR A

Set the FLAGS for Register A

3533

JR Z,3556H

If A was zero, then the cursor is off and we JUMP down to 3556H.

3535

LD A,(401CH)

Check to see if the cursor is to blink by loading (401CH) into A.
NOTE: 401CH holds the Cursor Blink Switch and will be 0 for Blink, and anything else for No Blink.

3538

OR A

Set the FLAGS for Register A

3539

JR NZ,3556H

If the system is set for No Blink, then JUMP to 3556H.

353B

LD HL,401AH

Load HL with 401AH.
NOTE: 401AH is the memory location that stores the cursor blink count.

353E

DEC (HL)

Reduce the memory contents of (401AH) by one.
NOTE: 401AH is the memory location that stores the cursor blink count.

353F

JR NZ,3556H

If that reduced count is still not zero, JUMP to 3556H.

3541

LD (HL),07H

Set the cursor blink count to 7.
NOTE: 401AH is the memory location that stores the cursor blink count.

3543

CALL 319DH

GOSUB to 319DH

3546

INC HL

Bump HL. This will increase HL from 401AH to 401BH.
NOTE: 401BH holds the cursor blink status - 0 = Off, Anything Else = On.

3547

LD A,(HL)

Load Register A with the memory contents pointed to by Register Pair HL.

3548

XOR 01H

XOR A with 01H.

354A

LD (HL),A

Put the toggled cursor blink status into the appropriate memory location.

354B

LD HL,(4020H)

Poll (4020H) and put the result into HL.
NOTE: 4020H holds the current cursor position.

354E

LD A,(4023H)

Load A with the memory contents of (4023H).
NOTE: 4023H holds the cursor character.

3551

JR NZ,3555H

If the CURSOR CHARACTER is NOT ZERO then JUMP to 3555H.

3553

LD A," "

LET Register A = the ascii character for a SPACE (since the CURSOR CHARACTER is ZERO)

3555H - Update the heartbeat and deal with the time, including rollover to the next day, month, and year.

3555

LD (HL),A

Put the contents of Register A into the memory location pointed to by (HL)

3556

LD HL,4216H

LET Register Pair HL = 4216H.
NOTE: 4216H is the heartbeat counter.

3559

DEC (HL)

Decrease the number held at (4216H) by 1.

355A

RET NZ

If the number held at (4216H) is not zero, then RETURN.

355B

LD (HL),1EH

Put a 1EH (Decimal: 30) into (4216H).
NOTE: 4216H is the heartbeat counter.

355D

CALL 319DH

GOSUB to 319DH

3560

INC HL

Bump HL by 1. HL will now point to 4217H, which is the memory location that holds the SECONDS.

3561

LD DE,0266H

Load DE with 0266H.
NOTE: 0266H points to the TIME DATA of the number of seconds in a minute, the number of mnutes in an hour, and the number of hours in a day.

3564

LD B,03H

Load B with a 03H, to set up a loop where we test seconds, minutes, and hours against their maximums.

3566

INC (HL)

Bump the number currently held in HL to increase the number stored there 1.
NOTE: If HL is 4217H then it is seconds, 4218H then it is minutes, 4217H then it is hours.

3567

LD A,(DE)

Poll the memory contents held at (DE) and put the result into A to get the maximum possible units for each time measure.
NOTE: 0266H points to the TIME DATA of the number of seconds in a minute, 0267H points to the number of mnutes in an hour, and 0268H points to the number of hours in a day.

3568

SUB (HL)

Compare the maximum to what we have by subtracting that maximum from the value pointed at in (HL).

3569

RET NZ

If there is no difference between what we have and the maximum then RETURN.

356A

LD (HL),A

If there is a difference, then put the difference into (HL) because we have to bump the next highest thing (seconds to minutes, minutes to hours, hours to days).

356B

INC HL

Bump HL.
NOTE: If HL is 4217H then it is seconds, 4218H then it is minutes, 4219H then it is hours, and 421AH then it is YEARS.

356C

INC DE

Bump DE.
NOTE: 0266H points to the TIME DATA of the number of seconds in a minute, 0267H points to the number of mnutes in an hour, and 0268H points to the number of hours in a day.

356D

DJNZ 3566H

Loop back to 3566H until the loop of 3 has been met, meaning that we have processed seconds, minutes, and hours.

356F

INC HL

Bump HL one more time, to 421BH.
NOTE: 421BH holds the current DAY portion of the date.

3570

INC (HL)

Bump the DAY portion of the date.

3571

INC HL

Bump HL one more time, to 421CH.
NOTE: 421BH holds the current MONTH portion of the date.

3572

LD A,(HL)

Get the month and put it into A.

3573

DEC HL

Decrease HL back to to 421BH.
NOTE: 421BH holds the DAY portion of the date.

3574

DEC A

Decrease A by one (to the previous month).
NOTE: DE currently points to the memory locations housing the of days in each month.

3575

ADD A,E

Add E to A.

3576

LD E,A

Load E with the result. E = E + A.

3577

LD A,(DE)

Poll the number of days in a month and put the result into A.

3578

CP (HL)

Compare A against (HL).
NOTE: If this is not a loop, the HL holds the day portion of the date.

3579

RET NC

If all of this shows that the current day of the month is less than the maximum number of days in a month, then RETURN because we don't need to bump anything more.

357A

LD A,(HL)

Load A with the current day of the month, as HL was pushed back to point to the day of the month at instruction 3571H.

357B

CP 1EH

Compare A to 1E (Decimal: 30).
NOTE: A CP actually subtracts 1E from A without modifying A, but the flags are set accordingly. Here, if A is < 1E then the CARRY FLAG will be set.

357D

JR NC,3585H

If the carry flag isn't set then JUMP to 3585H to update the MONTH, but not the YEAR.

357F

DEC HL

Decrement HL to now point to 421AH.
NOTE: 421AH points to the current YEAR.

3580

LD A,(HL)

Load the YEAR into A.

3581

INC HL

Bump HL to 421BH.
NOTE: 421BH points to the current DAY.

3582

AND 03H

Mask A (which is holding the year) with 03H (Binary: 00000011) to test for a leap year.

3584

RET Z

RETURN if that mask showed that we are in the 4th year of a cycle (because 04 and higher are turned off).

3585

LD (HL),01H

Put a 1 into the memory location pointed to by HL (which is DAY).

3587

INC HL

Bump HL to 421CH.
NOTE: 421BH points to the current MONTH.

3588

INC (HL)

Increase the current MONTH by 1.

3589

LD A,(HL)

Put the current MONTH into A.

358A

SUB 0DH

Subract 13 from A.
NOTE: This will test against a month 13. If A is < 13, then the CARRY FLAG will be set.

358C

RET C

If it is NOT month 13 then RETURN to skip the next code which increases the YEAR.

358D

LD (HL),01H

If we are here, then MONTH = 13, so set MONTH to 1.

358F

DEC HL

Decrement HL to 421BH.
NOTE: 421BH points to the current DAY.

3590

DEC HL

Decrement HL to 421AH.
NOTE: 421BH points to the current YEAR.

3591

INC (HL)

Bump the current year.

3592

RET

RETURN.

3593 - Check to see if the clock is on and exit back out if it is off OR the heartbeat shows that the clock was just updated. Pass through otherwise.

3593

LD A,(4210H)

Test to see if the clock is on by putting the contents of memory location 4210H into A.
NOTE: 4210H holds the bit mask for port ECH. Port ECH stores miscellaneous controls.

3596

RRCA

Rotate A to put Bit 0 into the CARRY FLAG.

3597

RET NC

If Bit 0 of A is ZERO, then return.

3598

LD A,(4216H)

If we are here, then the clock is on, so load A with the memory contents of (4216H) to see if the clock was just updated.
NOTE: 4216H is the heartbeat counter.

359B

CP 1EH

Compare the heartbeat counter against 1EH.
NOTE: A CP actually subtracts 1E from A without modifying A, but the flags are set accordingly.

359D

RET NZ

If the clock was not just updated, then RETURN.

359E

LD HL,3C35H

If the clock was just updated, then we need to display to screen so we set HL to the screen location of 3C35H which is the top line of the screen, 10 characters from the end of first line.

35A1 - Put the Clock 10 characters from the end of the first line. We enter this routine with HL pointing to the screen location 10 characters from the end of the first line.

35A1

LD DE,4219H

Set DE to 4219H.
NOTE: 4219H is the current HOUR.

35A4

LD C,3AH

Load C with a :.
NOTE: This routine is also used to convert the date, and C will be swapped out to a / for that routine.

35A6

LD B,03H

Load B with a 3.
NOTE: This is because we need to convert 3 numbers, so we will loop 3 times.

35A8

LD A,(DE)

Put the memory contents of DE into A.
NOTE: This will be HOUR (4219H) on the first pass, MINUTE (4218H) on the second pass, and SECOND (4219H) on the third pass.

35A9

DEC DE

Decrement DE to point to the next unit to be dealt with.

35AA

LD (HL),2FH

Load the memory location pointed to by (HL) with 2F.
NOTE: 2F is a / which is also 1 character below a 0.

35AC

INC (HL)

Increase whatever is held in (HL). On the first iteration, this change the character at the screen location to a 0.

35AD

SUB 0AH

A = A - 10. If A is < 10, then the CARRY FLAG will be set and if A is > 10, the NOT CARRY FLAG will be set.

35AF

JR NC,35ACH

Loop back 2 instructions if A > 10 [V!!!].

35B1

ADD A,3AH

If we are here, then A was less than 10, so we need to increase A by 3A (Binary: 0011 1010) to point to the ASCII number of the remainder.

35B3

INC HL

Bump HL to point to the next location on the video screen. On the first iteration, this will be the 2nd digit of the HOUR.

35B4

LD (HL),A

Put the ASCII value of the remainder onto the screen. On the first iteration, this will be the 2nd digit of the HOUR put into 4220H.

35B5

INC HL

Bump HL to point to the next location on the video screen. On the first iteration, this will be the 3rd character.

35B6

DEC B

Decrement B to the next unit. On the first iteration, this will move from 3 to 2.

35B7

RET Z

If we have processed all passes in the loop, RETURN.

35B8

LD (HL),C

If we are here, then the routine has not yet looped 3 times, so put a : onto the screen.

35B9

INC HL

Bump HL to point to the next location on the video screen.

35BA

JR 35A8H

JUMP back to 35A8H to continue the loop.

35BCH - Put the DATE 8 characters from the end of the first line. We enter this routine with HL pointing to the screen location and we just jump into the prior routine with a different pointer to the DATE and a change in the delimeter to a /.

35BC

LD DE,421CH

Load DE with 421CH.
NOTE: 421CH holds the current MONTH.

35BF

LD C,2FH

Load C with a /.

35C1

JR 35A6H

Jump into the above routine to convert the Month, Day, and Year.

35C3 - Maskable Interrupt Handler.

35C3

PUSH AF

Save AF to the STACK.

35C4

IN A,(E0H)

Poll Port E0H which is the MASKABLE INTERRUPT LATCH and put the results into A.

35C6

RRA

Rotate the contents of A one bit to the right, with the contents of the carry bit being moved to bit 7 and the contents of bit 0 being moved to the carry bit. If Bit 0 is low then NC will be set.

35C7

JP NC,3363H

If Bit 0 is low then JUMP to 3363H.

35CA

RRA

Rotate the contents of A one bit to the right, with the contents of the carry bit being moved to bit 7 and the contents of bit 0 being moved to the carry bit. If Bit 0 is low then NC will be set.

35CB

JP NC,3363H

If Bit 0 is low then JUMP to 3363H.

35CE

PUSH BC

Save all the registers.

35CF

PUSH DE

35D0

PUSH HL

35D1

PUSH IX

35D3

PUSH IY

35D5

RRA

Rotate the contents of A one bit to the right, with the contents of the carry bit being moved to bit 7 and the contents of bit 0 being moved to the carry bit. If Bit 0 is low then NC will be set.

35D6

PUSH AF

Save the contents of Register Pair AF to the STACK.

35D7

CALL NC,4046H

If Bit 0 is low then GOSUB to 4046H.
NOTE: 4046H is Interrupt Vector 2 and contains a JUMP to 35A9H. It is commonly used by the clock.

35DA

POP AF

RESTORE the last item in the STACK to Register Pair AF

35DB

RRA

Rotate the contents of A one bit to the right, with the contents of the carry bit being moved to bit 7 and the contents of bit 0 being moved to the carry bit. If Bit 0 is low then NC will be set.

35DC

PUSH AF

Save the contents of Register Pair AF to the STACK.

35DD

CALL NC,403DH

If Bit 0 is low then GOSUB to 403DH.
NOTE: 403DH is Interrupt Vector 3 and contains a JUMP to 35FAH.

35E0

POP AF

RESTORE the last item in the STACK to Register Pair AF

35E1

RRA

Rotate the contents of A one bit to the right, with the contents of the carry bit being moved to bit 7 and the contents of bit 0 being moved to the carry bit. If Bit 0 is low then NC will be set.

35E2

PUSH AF

Save the contents of Register Pair AF to the STACK.

35E3

CALL NC,4206H

If Bit 0 is low then GOSUB to 4206H.
NOTE: 403DH is Interrupt Vector 4 and contains a JUMP to 35FAH.

35E6

POP AF

RESTORE the last item in the STACK to Register Pair AF

35E7

RRA

Rotate the contents of A one bit to the right, with the contents of the carry bit being moved to bit 7 and the contents of bit 0 being moved to the carry bit. If Bit 0 is low then NC will be set.

35E8

PUSH AF

Save the contents of Register Pair AF to the STACK.

35E9

CALL NC,4209H

If Bit 0 is low then GOSUB to 4209H.
NOTE: 4209H is Interrupt Vector 5 and contains a JUMP to 35FAH.

35EC

POP AF

RESTORE the last item in the STACK to Register Pair AF

35ED

RRA

Rotate the contents of A one bit to the right, with the contents of the carry bit being moved to bit 7 and the contents of bit 0 being moved to the carry bit. If Bit 0 is low then NC will be set.

35EE

PUSH AF

Save the contents of Register Pair AF to the STACK.

35EF

CALL NC,4040H

If Bit 0 is low then JUMP to 4040H.
NOTE: 4209H is Interrupt Vector 6 and contains a JUMP to 35FAH.

35F2

POP AF

RESTORE the last item in the STACK to Register Pair AF

35F3

RRA

Rotate the contents of A one bit to the right, with the contents of the carry bit being moved to bit 7 and the contents of bit 0 being moved to the carry bit. If Bit 0 is low then NC will be set.

35F4

CALL NC,4043H

If Bit 0 (which was BIT 7) is low then JUMP to 4043H.
NOTE: 4043H is Interrupt Vector 7 and contains a JUMP to 35FAH.

35F7

POP IY

RESTORE the last item in the STACK to Register Pair IY

35F9

POP IX

RESTORE the last item in the STACK to Register Pair IX

35FB

POP HL

RESTORE the last item in the STACK to Register Pair HL

35FC

POP DE

RESTORE the last item in the STACK to Register Pair DE

35FD

POP BC

RESTORE the last item in the STACK to Register Pair BC

35FE

POP AF

RESTORE the last item in the STACK to Register Pair AF

35FF

Enable Interrupts.

3600

RET

RETURN.

3601 - RS-232 Initialization Routine. I'm [guessing] that IX is set to 41F5H

3601

Disable Interrupts so they don't interrupt this routine.

3602

IN A,(0EAH)

Poll Port EAH into A.
NOTE: Port EAH is the RS-232 UART Control Register/Status Register. Input:

Bit 3: Parity error (1=True)
Bit 4: Framing Error (1=True)
Bit 5: Overrun (1=True)
Bit 6: Data Sent (1=True)
Bit 7: Data Ready (1=True)

3604

INC A

INCrement Register A by 1 which means that any test for Z was really to see if Register A held FFH to identify if the RS-232 exists.

3605

JR Z,362DH

If the RS-232 does NOT exist, JUMP down to 362DH.

3607

OUT (E8H),A

Output A to port E8H which is the RS-232 Status Register & Master Reset. Outputting ANYTHING to Port E8H resets the RS-232.

3609

LD A,(IX+03H)

Load the BAUD RATE CODE into A.
NOTE: 41F8H holds the baud rate code.

360C

OUT (E9H),A

Output A to Port E9H.
NOTE: Port E9H is the RS-232 Baud Rate Selects and Sense Switches. Outputting to Port E9H will set the Baud Rate as follows:

Bits 0-3 - Select the Receive Rate
Bits 4-7 - Select the Transmit Rate

360E

LD A,(IX+04H)

Load the CONFIURATION CODE into A.
NOTE: 41F9 holds the RS-232 Configuration Code.

3611

OR A

Set the flags.

3612

JR Z,362DH

If the CONFIGURATION CODE in A is 0, then JUMP down to 362DH.

3614

OUT (0EAH),A

Output the CONFIGURATION CODE to Port EAH.
NOTE: Port EAH is the RS-232 UART Control Register/Status Register. For output:

Bit 0: Data Terminal Ready
Bit 1: Request to End
Bit 2: Break
Bit 3: Parity Enable
Bit 4: Stop Bits
Bit 5: Select
Bit 6: Word Length
Bit 7: Parity (0=Odd, 1=Even)

3616

CALL 3635H

GOSUB to 3635H [to CLEAR OPTIONS].

3619

LD A,(IX+05H)

Load the WAIT SWITCH into A.
NOTE: 41FAH holds the RS-232 Wait Switch.

361C

OR A

Set the flags.

361D

JR Z,3621H

If the WAIT SWITCH was ZERO, skip the next instruction and pick up at 3621H.

361F

LD A,02H

LET Register A = 02H (Binary: 0000 0010).

3621

OR 04H

OR Register A against 04H (Binary: 00000100) to turn on Bit 2.

3623

LD (41E9H),A

Put the contents of Register A into memory location 41E9H.
NOTE: 41E9H is the RS-232 Input DCB: Bit 2 is DRIVER ON or OFF.

3626

LD (41F1H),A

Put the contents of Register A into memory location 41F1H.
NOTE: 41F1H is the RS-232 Output DCB: Bit 2 is DRIVER ON or OFF.

3629

IN A,(E8H)

Poll Port E8H and put the result into A.
NOTE: Port E8H is the RS-232 Status Register & Master Reset. Input:

Bit 4: Ring Indicator
Bit 5: Carrier Detect
Bit 6: Data Set Ready
Bit 7: Clear to Send

362B

Enable Interrupts.

362C

RET

RETURN.

362D - This will zero out a bunch of RS-232 Related Ports and Memory Addresses. We wind up here if there is no RS-232 or the RS-232 CONFIGURATION CODE is 0.

362D

LD BC,04E8H

LET Register B = 04H and LET Register C = E8H. This saves a byte over the actual Model III Code which has those as 2 different instructions.

3630

OUT (C),A

Send Register A to the current port. On the first iteration, this is E8H (the RS-232 Status Register & Master Reset).

3632

INC C

INCrement Register C by 1 (to advance to the next port).

3633

DJNZ 3630H

JUMP back to 3630H until all 4 RS-232 ports have been reset.

3635

LD HL,41E8H

Load HL with 41E8H.
NOTE: 41E8 is the Input Buffer of the RS-232 Input DCB.

3638

XOR A

Clear A and all flags.

3639

LD B,03H

Load B with 3 as a counter. 3 is for 3 bytes - 41E8H, 41E9H, and 41EAH.

363B

LD (HL),00H

Load (HL) with 00H.

363C

INC HL

Bump HL.

363D

DJNZ 3649H

Loop back to 3649H until 3 bytes have been zeroed.

363F

LD HL,41F0H

Load HL with 41F0H.
NOTE: 41F0H is the 1 characer output buffer for the RS-232 Output DCB.

3642

LD B,03H

Load B with 3 as a counter. 3 is for 3 bytes - 41F0H, 41F1H, and 41F2H.

3644

LD (HL),00H

Load (HL) with 00H.

3645

INC HL

Bump HL.

3646

DJNZ 3644H

Loop back to 3644H until 3 bytes have been zeroed.

3648

JR 3629H

JUMP to 3629H.

364AH - RS-232 Input Routine.

364A

LD HL,41E8H

LET Register Pair HL = 41E8H.
NOTE: 41E8 is the Input Buffer of the RS-232 Input DCB.

364D

XOR A

Clear A and all flags.

364E

LD (HL),A

Put the contents of Register A into the memory location pointed to by (HL)

364F

INC HL

INCrement Register Pair HL by 1 to 41E9H.
NOTE: 41E9H is the RS-232 Input DCB:

Bit 2: Driver On/Off
Bit 1: Wait/No Wait

3650

BIT 2,(HL)

Test Bit 2 of 41E9H to see if the RS-232 is active.
NOTE: Bit 2 of 41E9 contains the DRIVER ON/OFF.

3652

RET Z

If the Driver is OFF, RETURN.

3653

DEC HL

DECrement Register Pair HL by 1. This will put HL back to 41E8H.

3654

CALL 3667H

GOSUB to 3667H to check the RS-232 Port for DATA READY and if so, takes in a character from the RS-232.

3657

JR Z,3665H

If the Z FLAG is set (meaning a byte was read from the RS-232 Port), JUMP to 3665H to put it into (HL) and RETURN.

3659

INC HL

INCrement Register Pair HL by 1. On the initial pass of this loop, this will put HL back to 41E9H.

365A

BIT 1,(HL)

Test Bit 1 of 41E9H to see if the RS-232 is active.
NOTE: Bit 1 of 41E9 contains the WAIT/NO WAIT.

365C

RET Z

If Bit 1 is ZERO, RETURN.

365D

CALL 028DH

GOSUB to 028DH to check for a BREAK key.

3660

JR Z,3653H

Loop back to 3653H until we get either a [???? whatever 3667H does ??????] or a BREAK key.

3662

JP 4203H

JUMP to 4203H

3665 - A JUMP here puts the character held in Register A (which was read from the RS-232C) and puts it in the memory location pointed to by HL; and then RETURN.

3665

LD (HL),A

Put the contents of Register A into the memory location pointed to by (HL)

3666

RET

RETURN.

3667 - RS-232 Input Routine - This checks for DATA READY and if so, takes in a character from the RS-232. Exits with NC set if DATA NOT READY.

3667

IN A,(EAH)

Poll Port EAH into A.
NOTE: Port EAH is the RS-232 UART Control Register/Status Register. Input:

Bit 3: Parity error (1=True)
Bit 4: Framing Error (1=True)
Bit 5: Overrun (1=True)
Bit 6: Data Sent (1=True)
Bit 7: Data Ready (1=True)

3669

OR A

Set the FLAGS for Register A

366A

RLCA

Rotate the bits in A left (with Bit 7 going into both the CARRY and Bit 0). By doing this, Bit 7 (DATA READY) is in the carry so NC = No.

366B

RET NC

If DATA READY wasn't set, RETURN.

366C

XOR A

Clear A and all flags.

366D

IN A,(EBH)

Poll Port EBH to A.
NOTE: Port EBH is the RS-232C Data Register. It contains the data received from the RS-232C.

366F

RET

RETURN.

3670 - RS-232 Input Routine - This SUBOUTINE Reads a Byte from the RS-232 until a 00H is read.

3670

CALL 3667H

GOSUB to 3667H to check the RS-232 for DATA READY and get a Byte into A.

3673

JR NZ,3670H

If the Byte from the RS-232 is not ZERO, then JUMP back to the prior instruction and read another byte.

3675

RET

RETURN.

3676 - RS-232 Output Routine.

3676

LD HL,41F1H

LET Register Pair HL = 41F1H.
NOTE: 41F1H is part of the RS-232 Output DCB:

Bit 2: Driver ON/OFF
Bit 1: Wait/No Wait

3679

BIT 2,(HL)

Test Bit 2 of 41F1H to see if the RS-232 is active.

367B

RET Z

If the RS-232 is NOT active, RETURN.

367C

IN A,(EAH)

If the RS-232 IS active, then Poll Port EAH into A.
NOTE: Port EAH is the RS-232 UART Control Register/Status Register. Input:

Bit 3: Parity error (1=True)
Bit 4: Framing Error (1=True)
Bit 5: Overrun (1=True)
Bit 6: Data Sent (1=True)
Bit 7: Data Ready (1=True)

367E

BIT 6,A

Test Bit 6 of Port EAH to see READY TO SEND.

3680

JR NZ,368DH

If READY TO SEND then skip forward to 368DH.

3682

BIT 1,(HL)

Test Bit 1 of 41F1H to see if the RS-232 is active.
NOTE: 41F1H Hholds DRIVER ON/OFF in BIT 2, and WAIT/NO WAIT in BIT 1.

3684

RET Z

If RS-232 is NOT active, RETURN.

3685

CALL 028DH

GOSUB to 028DH to check for a BREAK key.

3688

JR Z,367CH

JUMP to 367CH to poll again if there was NO BREAK.

368A

JP 4203H

JUMP to 4203H if the BREAK key was pressed.
NOTE: 4203H JUMPS to 022EH and is the break vector for tape and RS-232.

368D - Inside RS-232 Output Routine - If the RS-232 Returned READY TO SEND, then we are here to do the send..

368D

DEC HL

DECrement Register Pair HL by 1.

368E

LD A,(HL)

Load Register A with the memory contents pointed to by Register Pair HL.

368F

OR A

Set the FLAGS for Register A

3690

JR NZ,3693H

If A is NOT ZERO, then JUMP to 3693H

3692

LD A,C

LET Register A = Register C.

3693

OUT (EBH),A

Send A out of Port EBH which is the RS-232C Data Register. It contains the data to be sent to the RS-232C.

3695

LD (HL),00H

Put a 00H into the memory location pointed to by HL.
NOTE: HL is likely pointing to 41EEH, which is the Driver Address for the RS-232 Output DCB.

3697

RET

RETURN.

3698-36A9 - Message Storage Area for ROM Version

3698-36A9

Message Storage

U 1(24) 4-Jan-86

36AAH - Initial Vectors and DCBs for RAM 4000H-404BH.

36AA

C3 96 1C C3 78 1D C3 90 1C C3 D9 25 C9 00 00 C9 00 00 C3 18 30 01 24 30 00 01 07 00 00 07 73 04 00 3C 00 B0 00 06 C2 03 43 01 00 FF 00 C3 00 50 C7 00 00 AF C9 00 00 00 00 00 00 00 00 C3 00 36 C3 00 36 C3 00 36 C3 29 35 C7 00

36F5H - UNUSED.

36F5

00 00 00 00

36F9H - Initial Vectors and DCBs for RAM 41E5H-4224H.

36F9H-3728H

01 1E 30 00 00 00 60 1B 02 21 30 00 00 00 08 00 02 1B 30 55 6C FF 00 00 00 96 DC 05 00 00 C3 2E 02 C3 00 36 C3 00 36 3F 32 03 32 38 03 3C 04 00

3729H-3738H

00 1E 00 00 00 00 00 00 00 00 00 00 00 00 00

3739 - This is jumped to from the middle of the tokenize routine. It checks for items inside quotes.

3739

CP 22H

If the character in register A is not an end of the BASIC line character, then test the character against 22H to see if it is a ".

373B

JR NZ,3747H

If the character in register A is not a ", then JUMP forward a few instructions to 3789H.

373D

LD A,(409FH)

Load A with the memory contents of 409FH.
NOTE: 409FH is the DATA FLAG.

3740

XOR 01H

XOR A against 1 (Binary: 0000 0001).
NOTE: XOR is an exclusive OR, meaning that if the 2 things are the SAME the result is 0, and if the 2 things are DIFFERENT, the result is 1.

3742

LD (409FH),A

Load memory location 409FH with a the XOR'd results.
NOTE: 409FH is the DATA FLAG.

3745

LD A,22H

Load A with 22H, which is a ".

3747

CP 3AH

Compare A against 3AH (which is a :) doing A - 3AH. If A < 3AH, for UNSIGNED items, then the C FLAG is set. If A => 3AH, for UNSIGNED items, then the C FLAG is reset. If A = 3AH then the Z flag is set.

3749

JP NZ,06AAH

If A is 3AH then JUMP to 06AAH.
NOTE: 06AAH is in the middle of the KEYBOARD DRIVER ENTRY ROUTINE.

374C

LD A,(409FH)

Otherwise, Load A with the memory contents of 409FH.
NOTE: 409FH is the DATA FLAG.

374F

RRA

Rotate the contents of A one bit to the right, with the contents of the carry bit being moved to bit 7 and the contents of bit 0 being moved to the carry bit. If Bit 0 is low then NC will be set.

3740

JP C,06A8H

If Bit 7 of the DATA FLAG was set, then JUMP to 06A8H.
NOTE: 06A8H is in the middle of the KEYBOARD DRIVER ENTRY ROUTINE.

3743

RLA

Rotate A left one bit, with the contents of BIT 7 being put into the CARRY FLAG and the CARRY FLAG are put into BIT 0. This puts the read data into the CARRY FLAG.

3744

JP 06A3H

JUMP to 06A8H.
NOTE: 06A8H is the REM processor in the middle of the KEYBOARD DRIVER ENTRY ROUTINE.

3757 - I/O Re-Router.

3757

LD (IX+05H),00H

Put a 00H at the memory location pointed to by (IX+5), which is the first character of the source.

375B

INC (IX+04H)

INCrement the memory location pointed to by (IX+4), which is the second character of the destination.

375E

LD A,(IX+04H)

Load A with the character at the memory location pointed to by (IX+4) which is the second character of the destination.

3761

CP (IX+03H)

Compare A with the character at the memory location pointed to by (IX+3) which is the first character of the destination.

3764

RET NZ

IF the character at (IX+04H) is the same as the character at (IX+03H) then RETURN

3765

LD (IX+04H),01H

Put a 00H the memory location pointed to by (IX+4), which is the second character of the destination.

3769

RET

RETURN.

376A - This subroutine is called by the print routine when a 01H or LINE FEED or CARRIAGE RETURN is the current character.

376A

LD A,C

LET Register A = Register C.

376B

CP E0H

Compare A against E0H (Binary:1110 0000). Results:

If A=E0H it sets the ZERO FLAG
If A<E0H then the CARRY FLAG will be set
if A>=E0H then the NO CARRY FLAG will be set.

376D

JP NC,0043H

If A>=E0H then JUMP back to 0043H (which USED to be the KBLINE routine, but now just JUMPs to 0434H which is the routine which prints the character held in C).

3770

CP C0H

If we are here then A>=E0H, so lets further test to see if A is "C0H" or higher. Results:

If A=C0H it sets the ZERO FLAG
If A<C0H then the CARRY FLAG will be set
if A>=C0H then the NO CARRY FLAG will be set.

3772

JR C,377EH

If A<C0H then JUMP to 377EH

3774

SUB 0C0H

If we are here then A<E0H, but A=>C0H (i.e., betweem 160 and 191), so SUBTRACT C0H (Decimal: 64; or 1 character below "A") to Register A.

3776

LD B,00H

LET Register B = 00H

3778

LD C,A

LET Register C = Register A.

3779

LD HL,(4220H)

LET Register Pair HL the memory contents of 4220H and 4221H.
NOTE: 4220H-4221H is the destination device nName for ROUTE Routine. 2 Bytes

377C

ADD HL,BC

LET HL = HL + BC

377D

LD C,(HL)

LET Register C = the contents of the memory location pointed to by Register Pair HL.

377E

JP 0063H

JUMP to 0063H (which jumps to 041FH which is inside the PRINTER ROUTINE; C holds the printable character to be printed as determined by the PRINTER CHARACTER TABLE).

3781H Print Screen Routine. Used to be 01D9H-01F7H

3781

LD HL,3C00H

Load HL with the memory location for the beginning of the video RAM.

3784

LD A,(HL)

Put the character at the screen location stored in HL into A.

3785

RLCA

Rotate the bits in A left (with Bit 7 going into both the CARRY and Bit 0). This will double as a test of Bit 7 since that is now sitting in the CARRY.

3786

LD A,2EH

Overwrite the current character held in Register A with a ., so that all graphic characters are printed as .'s.

3788

JR C,378BH

If Bit 7 of A was HIGH, then A is a graphics character, so skip 1 instruction

378A

LD A,(HL)

Load Register A with the memory contents pointed to by Register Pair HL.

378B

CALL 003BH

Call the PRINT CHARACTER routine at 003B (which sends the character in the A register to the printer).

378E

INC HL

Bump HL to the next character on the screen.

378F

BIT 6,H

Check the 6th Bit in H to see if we are at the end of the line (meaning that H is now 64; 1 character beyond the 63 maximum per lime).

3791

JP NZ,0214H

If we are at 64, then JUMP to 0214H for a new line.

3794

LD A,L

Test of end of line by loading A with L.

3795

AND 03FH

AND the contents of A with 3FH (Binary: 00111111) to turn off Bits 7 and 6, making the maximum number A can be 3FH (Decimal: 63).

3797

CALL Z,0214H

If that AND turned A to ZERO, then we are at the end of a line, so GOSUB to 0214H for a new line.

379A

JR 3784H

Loop back to 3784H for the next character.

379C - This is part of the warm reset routine from 3015H and fires right after interrupt mode is set to 1, non maskable interrupts are turned off, and the stack pointer is reset to 407DH.

379C

SCF

Set the CARRY FLAG.

379D

DB EDH

Define Byte EDH

379E

INC A

INCrement Register A by 1. I presume this means Register A = 1.

379F

JR C,37B9H

If the CARRY FLAG is still set even after the INC, then JUMP to 37B9H.

37A1

OUT (32H),A

OUTput the value held in Register A to Port 32H.

37A3

OUT (30H),A

OUTput the value held in Register A to Port 30H.

37A5

OUT (38H),A

OUTput the value held in Register A to Port 38H.

37A7

OUT (39H),A

OUTput the value held in Register A to Port 39H.

37A9

OUT (33H),A

OUTput the value held in Register A to Port 33H.

37AB

INC A

INCrement Register A by 1.

37AC

DB EDH

Define Byte EDH

37AD

ADD HL,SP

LET HL = HL + SP (SP sould be 407DH). Unless I am missing something Register Pair HL would be 00H at this point.

37AE

INC (HL)

INCrement the value held in the memory location pointed to by Register Pair HL.

37AF

LD A,82H

LET Register A = 82H

37B1

DB EDH

Define Byte EDH

37B2

ADD HL,SP

LET HL = HL + SP

37B3

LD (HL),3EH

Put 3EH (>) into the memory location pointed to by Register Pair HL.

37B5

RET P

Return if the Register Pair HL is still positive.

37B6

DB EDH

Define Byte EDH

37B7

ADD HL,SP

LET HL = HL + SP

37B8

LD A,(D03EH)

Z-80 TRICK. This command would be meaningless, and hopefully fill A with a 0.

37B9

LD A,D0H

If jumped to from 379F then LET Register A = D0H.

37BB

OUT (0F0H),A

Output the byte stored in Register A to Port F0H which is the FDC Status Register. Output Commands:

00H - restore
80H - read sector
A0H - write normal sector
A1H - write read protect sector
C0H - read address
D0H - reset; puts FDC in mode 1
E0H - read track
F0H - write track

37BD

PUSH BC

Save the value in Register Pair BC to the STACK.

37BE

POP BC

RESTORE the last item in the STACK to Register Pair BC

37BF

PUSH BC

Save the value in Register Pair BC to the STACK.

37C0

POP BC

RESTORE the last item in the STACK to Register Pair BC

37C1

RET

RETURN.

37C2H - This SUBROUTINE is called inside the HARD DRIVE routine once the READY status is set. On entry A is either 10H (Binary: 0001 0000; Bit 4 on) or 20H (Binary: 0010 0000; Bit 5 on).

37C2

OUT (CFH),A

OUTput A to Port CFH.
NOTE: Port CCH is Register 7 for WD1010 Winchester Disk Controller Chip and is the Hard Disk Error Command Register when used for OUTput. 70H is "Seek with a 35 milisecond stepping rate". 16H is "Restore with a 3 milisecond stepping rate"

37C4

CPL

Complement the value in register A. If Register A was 10H then Register A = 1110 1111. If Register A was 20H then Register A = 1101 1111.

37C5

RLCA

Rotate the bits in A left (with Bit 7 going into both the CARRY and Bit 0). This will double as a test of Bit 7 since that is now sitting in the CARRY.

37C6

IN A,(CFH)

Poll Port CFH and put the result into A.
NOTE: Port CFH is Register 7 for WD1010 Winchester Disk Controller Chip and is the Hard Disk Error Status Register when used for INPut.

37C8

JR C,37C5H

If the CARRY FLAG is set, JUMP to 37C5H

37CA

BIT 0,A

Check BIT 0 of Register A.
NOTE: Bit 0 is LOW on Port CFH if there is no error.

37CC

RET Z

If the ZERO flag is set, RETURN.

37CD - This is inside the HARD DRIVE routine once the READY status is set. If we are here, we got an error on the read despite the drive being READY.

37CD

LD A,1CH

LET Register A = 1CH (Binary: 0001 1100).

37CF

OUT (0C1H),A

OUTput a 1CH (Binary: 0001 1100) to Port C1H.
NOTE: Port C1H is the hard drive controller board control register. Sending Bit 3 high means ENABLE CONTROLLER and Bit 4 high means RESET CONTROLLER.

37D1

LD A,0CH

LET Register A = 0CH (Binary: 0000 1100).

37D3

OUT (0C1H),A

OUTput a 0CH (Binary: 0000 1100) to Port C1H.
NOTE: Port C1H is the hard drive controller board control register. Sending Bit 3 high means ENABLE CONTROLLER .

37D5

JR 37BDH

JUMP to 37BDH to do 2 pushes and 2 pops a delay and then RETURNs.

37D7H - I don't see that this is ever called or executed.

37D7

LD C,A

LET Register C = Register A.

37D8

LD B,B

LET Register B = Register B.

37D9

LD B,H

LET Register B = Register H.

37DA

EX AF,AF'

EXchange the values of AF and AF'

37DB

DEC D

DECrement Register D by 1.

37DC

NOP

37DD

DJNZ 37F1H

JUMP to 37F1H and keep doing that until B = 0.

37DF

NOP

37E0

DEC BC

DECrement Register Pair BC by 1.

37E1

NOP

37E2

NOP

37E3

NOP

37E4

NOP

37E5

NOP

37E6

NOP

37E7

NOP

37E8H - Hidden 2 Byte Code - Printer Input/Output.

37E8

N/A

The equivalent of testing port F8H for status. If you PEEK this location, you will get the PRINTER STATUS (63 = Printer ON; 143 = Printer Off) rather than what may actually be contained at this ROM location. Thanks to George Philips for this info!

37E9

N/A

The equivalent of sending a byte to port F8H. If you POKE this location, you are sending a byte to the PRINTER. Thanks to George Philips for this info!

37EAH - BASIC TIMES (DATE$+" "+TIME$)

37EA

RST 10H

Call the EXAMINE NEXT SYMBOL routine at RST 10H which loads the next character from the string pointed to by the HL register into the A-register and clears the CARRY FLAG if it is alphabetic, or sets it if is alphanumeric.

Blanks and control codes 09H and 0BH are ignored causing the following character to be loaded and tested.

The HL register will be incremented before loading any character therfore on the first call the HL register should contain the string address minus one.

The string must be terminated by a byte of zeros.

37EB

PUSH HL

Save HL (the current position) to the STACK.

37EC

LD A,11H

Load A with 11H (Decimal: 17).
NOTE: This is to set up for a 17 Byte String.

37EE

CALL 2857H

GOSUB to 2857H to create the string.

37F1

LD HL,(40D4H)

Load HL with the memory contents of (40D4H).
NOTE: 40D4 is the string pointer.

37F4

CALL 35BCH

GOSUB to 35BCH.
NOTE: 35BCH populates the DATE$ and puts it on the screen.

37F7

LD (HL),20H

Load the memory location pointed to by HL with a SPACE.

37F9

INC HL

Increment HL to move 1 character over.

37FA

CALL 35A1H

GOSUB to 35A1H.
NOTE: 35A1H populates the TIME$ and puts it on the screen.

37FD

JP 2884H

JUMP to 2884H, which is in the middle of the STRING routine.

Model III ROM Explained - Part 4 (Durda ROM)

Introduction

3000 - Jump Table.

303C-303F - Frank Durda IV's Initials

3040-3047 - No Location Jumps Here. This may have been a Frank Durda Embedded Serial Number of 98 36 C3 7D 30 C3 6A 37.

3048 - This subroutine is called by the print routine when a LINE FEED or CARRIAGE RETURN is the current character.

304B - Part of the Network 4 Controller Boot - GOSUB'ed by 3076H and 30ECH

304B - Part of the Network 4 Controller Boot - This was JUMPed to from 30EAH. This routine appears to process the CASS? answer, but beyond just H and L.

309C - This subroutine will display the message held in HL and then JUMP to the KBWAIT (Wait for Keypress) Routine.

30A2 - This is a VECTOR JUMP from 3015H - It resets all the ports, sets the interrupt to jump to 4046H, moved 76 bytes from 36AAH to 4000H, and reads disk sectors into 4000H+ until the interrupt fires.

313B - This routine will clear the stack, check the floppy drive status register after a read, and JUMP to 4300H to continue to DOS if successful, and jump to 310BH if errors were found.

314E - Hard Drive Routine - This routine is jumped from 3107H if the last disk read did not produce any of CRC ERROR, SEEK ERROR, and NOT READY.

319DH - This SUBROUTINE is called by 3543H and 355D.

31A5H - This SUBROUTINE is called by 3245H and 352CH. it writes 14 .46 volt pulses to tape, 14 .00 volt pulses to tape, waits for 78H loops, and RETURNS.

31BDH - This SUBROUTINE resets the cassette, sets the NMI, turns on interrupts, and RETURNs. It is ALSO a VECTOR jump from 400CH.

31D1 - Turn On The Cassette - Part 1. This will remove the return address, save DE and BC, restore the return address, and than blank the "**"

31E8 - Turn On The Cassette - Actually Set the Bit Mask and Output the Command

31F3 - Reset the Cassette Port. This routine OUTputs a 0 to the Cassette Port FFH

31F7 - Check to see if we have a PRINT # command and, if so, get the port number, validate that the next character is a , and return.

3203 - Vector for a SLOW cassette read. Frank saved 2 bytes by putting the memory addresses into BC and then using 1 byte instructions to maipulate the memory address.

321E - Cassette - Keep reading tape looking for a timing mark or BREAK.

322C - Cassette - Wait for the timing mark to pass and the next data to show up. Put that data into Bit 0 of D.

323FH - Vector for a SLOW cassette write. On entry A is the byte to output.

3256H - "Write a 0 Bit" by simply waiting the appropriate amount of time and doing nothing.

325C - SLOW tape header write

3272 - SLOW tape header read

3299 - FAST tape header write.

32B2 - Restore all registers from the STACK, and Fill C with A, and JUMP to cassette write.

32B8 - Save all registers to the STACK, and Fill C with A, GOSBUB to write out the START BIT ...

32BF - Call 3335H to Output a Bit 8 Times

32CAH - Read the start bit, read 8 bits, check for error, and flash the star

32D8H - FAST tape header read.

334EH - READ a BIT

3363 - This is a Port E0H Masked Jump. If the MASKABLE INTERRUPT is xxxxxxx1, it jumps here.

337AH - Check for a Data Error.

338CH - Keyboard Routine - VECTORed from 3024H.

33C5H - Inside Keyboard Routine - JUMPed to from the XOR commands above

33F2 - Inside Keyboard Routine

3404 - Inside Keyboard Routine

3440 - Inside Keyboard Routine

3446 - Inside Keyboard Routine

3468 - Inside Keyboard Routine

346C - Inside Keyboard Routine

348D - Inside Keyboard Routine

34AA - Inside Keyboard Routine

34B6 - Inside Keyboard Routine

34C1 - Inside Keyboard Routine

34CFH - Inside Keyboard Routine - I'm not convinced that the code here did anything.

34E5 - Network 4 BOOT Routine - Jumped here if the keypress was not a 3.

3518 - This SUBROUTINE is called during WARM BOOT. It handles setting up the Port 84H Settings (as explained in this section).

3523H - This SUBROUTINE tests the active CPU SPEED and sets Z accordingly (Z=2mhz, NZ=4mhz)

3529 - Deal with the cursor.

3555H - Update the heartbeat and deal with the time, including rollover to the next day, month, and year.

3593 - Check to see if the clock is on and exit back out if it is off OR the heartbeat shows that the clock was just updated. Pass through otherwise.

35A1 - Put the Clock 10 characters from the end of the first line. We enter this routine with HL pointing to the screen location 10 characters from the end of the first line.

35BCH - Put the DATE 8 characters from the end of the first line. We enter this routine with HL pointing to the screen location and we just jump into the prior routine with a different pointer to the DATE and a change in the delimeter to a /.

35C3 - Maskable Interrupt Handler.

3601 - RS-232 Initialization Routine. I'm [guessing] that IX is set to 41F5H

362D - This will zero out a bunch of RS-232 Related Ports and Memory Addresses. We wind up here if there is no RS-232 or the RS-232 CONFIGURATION CODE is 0.

364AH - RS-232 Input Routine.

3665 - A JUMP here puts the character held in Register A (which was read from the RS-232C) and puts it in the memory location pointed to by HL; and then RETURN.

3667 - RS-232 Input Routine - This checks for DATA READY and if so, takes in a character from the RS-232. Exits with NC set if DATA NOT READY.

3670 - RS-232 Input Routine - This SUBOUTINE Reads a Byte from the RS-232 until a 00H is read.

3676 - RS-232 Output Routine.

368D - Inside RS-232 Output Routine - If the RS-232 Returned READY TO SEND, then we are here to do the send..

3698-36A9 - Message Storage Area for ROM Version

36AAH - Initial Vectors and DCBs for RAM 4000H-404BH.

36F5H - UNUSED.

36F9H - Initial Vectors and DCBs for RAM 41E5H-4224H.

3739 - This is jumped to from the middle of the tokenize routine. It checks for items inside quotes.

3757 - I/O Re-Router.

376A - This subroutine is called by the print routine when a 01H or LINE FEED or CARRIAGE RETURN is the current character.

3781H Print Screen Routine. Used to be 01D9H-01F7H

379C - This is part of the warm reset routine from 3015H and fires right after interrupt mode is set to 1, non maskable interrupts are turned off, and the stack pointer is reset to 407DH.

37C2H - This SUBROUTINE is called inside the HARD DRIVE routine once the READY status is set. On entry A is either 10H (Binary: 0001 0000; Bit 4 on) or 20H (Binary: 0010 0000; Bit 5 on).

37D7H - I don't see that this is ever called or executed.

37E8H - Hidden 2 Byte Code - Printer Input/Output.

37EAH - BASIC TIMES (DATE$+" "+TIME$)

321E - Cassette - Keep reading tape looking for a timing mark or `BREAK`.