TRS-80 DOS - NEWDOS/80 v2.0 for the Model I - SUPERZAP/CMD Disassembled

SUPERZAP/CMD

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NEWDOS/80 v2.0 SUPERZAP/CMD Disassembly - Apparat's SUPERZAP/80 (Model I)

SUPERZAP/CMD (manual section 6.1) shows and changes 256-byte disk sectors and pages of main memory. It can show a sector of a drive (by relative sector or by track and sector), of a file, a page of memory or a page of a memory dump file made by DUMP; search them for one to four bytes; change them byte by byte; verify, zero and copy ranges of sectors; copy any string of bytes from one place on a diskette to another; and show the codes the DOS stores for a password and for a file name and type. The display and the questions identify it as APPARAT'S SUPERZAP/80.

The file has four load blocks: 5200H-52FFH (code and a zero block the stack uses), 5420H-543FH (the FCB template), 5480H-5486H and 5491H-6FFDH (the variables, the code, the tables and messages, and 254 unused zero bytes); transfer address 54C5H. 5300H-541FH (sector buffer and FCB), 5440H-547FH (the answer line) and 5487H-5490H (number text) are not in the file. The page shows every byte of the file once, in address order; each row says what every register and address it uses holds at that moment.

Menu Functions

Display Mode

Modify Mode

Messages

Disk Errors

5200H - Display Address of a Dump Page

Called by the DM and DMDB print loop at 5692H before each page. For DM the page to show is the memory page itself, so its address at 54B4H is copied to 5495H, the address of the 256 bytes the display routine shows. For DMDB (bit 3 of 5491H) the page has been read into the sector buffer at 5300H, which 5495H already holds, so nothing is changed. Returns Register A = the command flags at 5491H.

520DH - Search: Start Positions

Two entries used by the F and L search (5856H, 585DH) when the search is to start at the very beginning. 520DH sets Register L, Register H and Register C to Register E (00H): the 24-bit file position in Register C, Register H and Register L is 0, and 54C3H, the page address shown during a memory search, becomes 0000H. 5214H is the DMDB form: the page address becomes the dump's base page (the high byte at 54B3H with a low byte of Register L).

521AH - Stack Area (Zero Bytes)

No instruction in SUPERZAP reads these 230 zero bytes or jumps into them. The Stack Pointer is set to 5300H at 54C5H and 56C1H, so the stack grows down from 52FFH into this block.

5300H - Sector Buffer and FCB (not in the file)

These areas are not loaded from the file. 5300H-53FFH is the main sector buffer (the DD, DTS and DFS sector, the DMDB page, the destination sector of CDD); 5400H-541FH is the one FCB SUPERZAP uses for every disk access, filled from the template at 5420H by the LDIR at 54DEH.

5420H - FCB Template

Data loaded from the file and copied to 5400H-541FH by the LDIR at 54DEH (Register Pair HL = 5420H, Register Pair DE = 5400H, Register Pair BC = 0020H) every time the menu is shown. The layout is the NEWDOS/80 FCB: open, with NEXT and EOF counted in sectors of the whole diskette, so that 4436H and 443CH read and write any sector of a drive.

5440H - Variables

The input line buffer 5440H-547FH and the number text buffer 5487H-5490H are not in the file. The variables at 5480H-5486H and 5491H-54C4H are loaded with the values shown; the Variables section of the introduction gives each one's use in the two-line form.

54C5H - Start and the Menu

SUPERZAP's transfer address. Every function comes back here when it ends: the X key, an empty filespec, PRESS 'ENTER' TO RETURN TO MENU (658BH), an X typed as a parameter (681DH). The stack is put back at 5300H, the state flags are cleared, the FCB is set up again from its template and the menu is shown. The answer is looked up in the command table at 690DH; an empty answer is DD.

550BH - Command Found: ,P and the Flags

Register Pair DE is at the entry's flags byte and Register Pair HL at the answer character after the name. Only ,P or nothing may follow; anything else continues the search with the next entry (so DM can fail and DMDB match). ,P needs bit 0 of the flags. The flags go to 5491H (with bit 1 for ,P) and 5492H; a function with bit 3 of the second byte (RRT) is refused under DOS-CALL. Then the handler is entered with JP (HL).

5545H - DTS: Display a Track's Sector

Asks DRIVE, TRACK AND SECTOR #'S? (J restarts here). An empty answer reads the sector the variables already name. 5554H is the K re-entry, which keeps the drive and asks TRACK AND SECTOR #'S?; 5563H asks only the sector. Each answer is checked by 670FH (drive), 6732H (track) and 6751H (sector); a bad one asks the same question again. The relative sector within the drive is track x sectors per track + sector.

5584H - DD: Display a Disk Sector

Asks DRIVE AND RELATIVE-SECTOR-WITHIN-DRIVE #'S? (also the empty menu answer and J). 5593H is the K re-entry, which keeps the drive. 55A0H reads the drive's sizes again; 55A7H sets the FCB's EOF to the drive's sector count, 55ADH the sector number. With ,P the sectors are printed through the VDS loop (5BB8H); otherwise the sector is read into 5300H and the display mode starts at 56BAH. 55ADH is also where R, + and - of the display mode come back for a disk sector.

55C5H - DFS and DMDB: Open the File

55C5H is the error exit of the open: SYS0 4409H displays the DOS error (bits 7 and 6 set, so it returns) and the filespec is asked again. 55CAH asks FILESPEC? (also J for DFS and DMDB); an empty answer goes back to the menu. The file is opened with SYS0 4424H, buffer 5300H, record length 256. The FCB's bit 6 of byte 1 is set, and the file's drive becomes the current drive. DMDB goes on at 55F7H, DFS asks for the sector within the file at 5641H.

55F7H - DMDB: The Dump's Base Address

A memory dump file made by DUMP starts with the address the dump was taken from, followed by the memory bytes. The file's first sector is read, its first two bytes become the base address at 54B2H and are shown as xxxxH = DUMP'S BASE MEMORY ADDRESS. 5623H then asks DUMP MAIN MEMORY ADDRESS? (also the K command); the address is cut to its page. With ,P the pages are printed from 5668H, otherwise 617BH reads the page from the file into 5300H and the display mode starts.

5641H - DFS: The Sector Within the File

Asks RELATIVE-SECTOR-WITHIN-FILE #? (also the K command of DFS). The answer is stored at 54A2H and 55ADH reads that sector of the file (NEXT counts file sectors, because the open cleared the FCB's whole-diskette bit).

564FH - DM: Display Main Memory

Asks MAIN MEMORY ADDRESS? (also the K command of DM). The address is cut to the start of its page and stored at 54B4H. Without ,P the display mode shows that memory page directly (56BDH); with ,P BYTE COUNT? is asked and the pages are printed.

5668H - DM,P and DMDB,P: Print Pages

Asks BYTE COUNT? and prints that many bytes, one display page of 16 lines of 16 bytes at a time: each page is shown and then copied line by line to the printer by 613AH. A last part page prints only the lines it needs. Then FUNCTION COMPLETED. For DMDB each page is read from the file first.

56A9H - Sector Out of Range from the Display Keys

Reached when - is pressed at relative sector 0 (576EH) or a dump read runs past the end of its file (61BCH): SOURCE SECTOR OUT OF RANGE is displayed, ENTER is awaited and the K command is run, which asks for the position again. 56AEH is also used by SCOPY (5800H) to show FUNCTION COMPLETED and run R.

56BAH - Display Mode: Show the Page and Read a Key

56BAH points the display at the sector buffer 5300H, 56BDH at the address in Register Pair DE (a DM memory page). 56C1H is the display mode loop, entered after every command: the stack is reset, the 256 bytes and the position are shown (5FB2H). After a search match the matched byte is marked with a blinking thin cursor until a key is pressed; otherwise a key is awaited. Keys of 20H and above are shown down column 6. M (MOD, not for DMDB), X (menu), E (EXIT), S (SCOPY), F (find), L (load module find, DFS only) are handled here; ; is taken as + and = as -, then 5716H clears the screen and 571BH handles J, K, R, + and -. Any other key shows the page again.

571BH - Display Mode: J, K, R, + and -

J restarts the function with all its questions (not DM, where J only shows the page again). K restarts keeping the first answer: DM asks the address, DFS the file sector, DMDB the dump address, DTS the track and sector, DD the relative sector. For a disk sector R reads the same sector again, + the next and - the previous one (- at sector 0 gives SOURCE SECTOR OUT OF RANGE); for DM and DMDB they change the page number at 54B5H. Any other key shows the page again.

5795H - SCOPY: Copy the Shown Sector to Another

DD and DTS only, typed as S then COPY. The source location is shown with IS TO BE COPIED TO and the destination drive and sector are asked (an empty or bad answer goes back to the menu). The destination is read into 4200H only to find its status, which is reported (SECTOR NOT READABLE, SECTOR READ PROTECTED, SECTOR NOT READ PROTECTED); then SHALL IT BE READ PROTECTED??? decides how the buffer at 5300H is written there. Afterwards FUNCTION COMPLETED and R, which shows the destination sector.

5803H - Display Mode: Match the Rest of a Command

Called with the text to match right after the CALL (COPY, XIT, OD, each ended by 00H). Each key (shown down column 6) must equal the next character; a wrong key shows the page again (56C1H resets the stack). After the 00H the routine continues at the instruction after the text.

5814H - EXIT

E in the display mode must be followed by XIT. 581BH is also the handler of the menu's EXIT: the screen is cleared and SUPERZAP leaves through 402DH to DOS READY.

5821H - Search: F and L

The display mode search for one to four bytes. L (DFS only) must be followed by a comma; F followed by ENTER goes on from the last match with the same bytes. After F or L: a comma starts at the beginning of the drive, file, memory or dump, two hexadecimal digits xx start at byte xx of the page shown; then a comma and up to four bytes aa,bb,cc,dd in hexadecimal, or ENTER to use the bytes of the last search. Each key is shown down column 6 and any wrong key shows the page again. The position is a 24-bit value in Register C (high), Register H and Register L (low): a byte position within the drive or file, or a memory address. For DMDB it is a position in the dump file, 2 more than the address minus the base.

58BFH - Search: The Compare Loop

Each pass starts one byte further on: the byte at the search position is read (593CH) and the position moved on; for a disk the sector and offset of that byte are kept at 54A2H and 54C2H, for memory the page at 54C3H. If it equals the first search byte, the following bytes are read and compared. Holding the up-arrow key stops the search and shows the page reached. A match sets bit 4 of 5493H, so the display marks the byte at 54AEH; then R shows the page.

593CH - Search: Read the Byte at the Position

Returns the byte at the position (Register C low, Register L, Register H) in Register B and moves the position on by one. DM reads memory: Register L is the address high byte and Register H must stay 00H (past FFFFH the search ends). The others read the file or drive with 5990H; an L search drops the load record headers, so only the bytes of load blocks are returned: 54BFH counts the bytes left in the current block.

5990H - Search: Read a Byte of the Drive or File

Positions the FCB at the byte Register C of sector Register Pair HL with SYS0 444EH and reads it with ROM 0013H. Error 06H (the sector is read protected) still leaves the data in the buffer, so the byte is taken from there. Error 1CH or 1DH (the end) gives NO MATCH; any other error is displayed and the menu shown.

59B4H - Search: No Match

The search reached the end. The search position goes back to the start (the first byte; for DMDB byte 2 of the file and page address 54B2H, the address of the base address variable), NO MATCH is shown after clearing the screen and K is run, which asks for the position again.

59E0H - CDD: Copy Disk Data

Copies any string of bytes from one place on a diskette to another. After the heading COPY DISK DATA (after seven asterisks) and SURE YOU WANT TO DO THIS??? the source drive, relative sector and byte offset are asked, then the destination's, then BYTE COUNT?. The source values move to 549AH (drive), 54A4H (sector), 54AFH (offset) and 54AAH (drive size); the destination stays in 5499H, 54A2H, 54AEH and 54A8H. 6111H decides whether the copy must run backwards because the ranges overlap. Source sectors are read into 4200H, destination sectors into 5300H; each destination sector is written back when it is full, keeping its read protection status.

5AACH - CDD: Source and Destination Sectors

5AACH reads the source sector at 54A4H on drive 549AH into 4200H (checked against 54AAH) and steps 54A4H on (back for a backward copy). 5AD2H writes 5300H to the destination sector at 54A2H with the status its read found, and steps 54A2H. 5AEFH writes and then reads the next destination sector with 5AF2H, which checks it against 54A8H and keeps its status in the operand at 5AD6H, because source reads change 5494H in the meantime. All keep Register Pair HL, Register Pair DE and Register Pair BC.

5B16H - Read and Write a Sector With a Range Check

5B16H sets the FCB from Register Pair HL (sector), Register Pair BC (buffer) and Register A (drive), checks the sector against Register Pair DE (SOURCE SECTOR OUT OF RANGE; not done for DFS and DMDB, where the DOS checks the file) and reads it with 6457H. 5B29H writes the buffer at 5300H to the sector at 54A2H on drive 5499H after checking it against 54A8H (DESTINATION SECTOR OUT OF RANGE). 5B42H only sets the FCB.

5B4DH - CDS, ZDS and VDS

CDS asks COPY DISK SECTORS??? (after seven asterisks) and SURE?, the source drive and sector (moved to 549AH, 54A4H, 54AAH), the destination (5499H, 54A2H, 54A8H) and SECTOR COUNT?; an overlapping copy on one drive runs from the last sector down. ZDS (5B9EH) asks ZERO DISK SECTORS??? (after seven asterisks) and SURE?, VDS (5BA6H) PAUSE WHEN SECTOR READ PROTECTED??? (Y sets bit 5 of 5493H); both then ask the drive and sector and SECTOR COUNT? (5BB3H). 5BB8H is also the ,P path of DD, DTS and DFS.

5BBBH - The Sector Loop of VDS, ZDS, CDS and ,P

For each sector: read it (CDS reads the source; the others the sector at 54A2H). A skipped error sector goes on to the next one. With ,P the sector is shown and printed. VDS stops when the up-arrow key is held and pauses at a read protected sector if asked. ZDS zeroes the buffer and writes it back, CDS writes the buffer to the destination; both keep the status the read found, so read protection is kept (ZDS) or copied (CDS). Then both sector numbers move on (or back) and the count at 54ACH is counted down; at 0 FUNCTION COMPLETED.

5C5AH - MODxx: The Modify Mode

M in the display mode (not DMDB) must be followed by OD and two hexadecimal digits xx, the byte where the cursor starts. Register L is the cursor's byte offset in the page and bit 0 of Register B the digit (0 the high digit, 1 the low one); bit 1 of Register B is set when the cursor has run past the last byte, and a hexadecimal digit typed then is refused. After every key the page is shown again with a blinking block on the digit. Hexadecimal digits change the byte at once (in memory for DM, in the buffer for a sector); space and right arrow move one digit on, left arrow one back, shift right and shift left two bytes, down arrow and up arrow 16 bytes (one line), all inside the page. ENTER ends (5D01H), Q cancels a sector change (5D34H), ZTxx and RTxx,jk fill a range (5D45H); anything else gives INVALID MODIFICATION MODE CHAR.

5D01H - Modify Mode: ENTER and Q

For DM, ENTER only ends the modify mode (the memory is already changed): MODIFICATION COMPLETED. For a sector the screen asks REPLY 'Y' IF OK TO WRITE MODIFIED SECTOR TO DISK: Y writes the buffer to the sector at 54A2H, keeping its read protection, and shows MODIFICATION COMPLETED; any other key goes back to the modify mode. Q (sectors only) shows MODIFICATION CANCELLED; after ENTER, R reads the sector again, which drops the changes.

5D45H - Modify Mode: ZTxx and RTxx,jk

Z or R, then T, two digits xx (the last byte of the range) and for R a comma and two digits jk (the new value), then ENTER; the keys are shown down column 6. Every byte from the cursor to byte xx becomes 00H (ZT) or jk (RT); when the cursor is on a low digit, the first byte keeps its high digit. The fill value is put into the operand at 5D9CH. The cursor ends on the high digit of the byte after xx. A wrong key, or xx before the cursor, gives INVALID MODIFICATION MODE CHAR.

5DBCH - Blink a Cursor and Wait for a Key

Register A is the cursor character (95H for a match, BFH for the modify mode), Register C the byte offset in the page, bit 0 of Register B the digit. The digit's place on the display is 3C08H + row x 64 + group x 5 + byte x 2 + digit, where the row is the offset's high four bits, the group (two bytes each) bits 3-1 and the byte in the group bit 0. The cursor character and the digit take turns, each for up to 256 keyboard scans, until a key is pressed; the digit is put back and the key returned in Register A.

5DF7H - Keys of the Display Mode Commands

5DF7H waits for a key and shows it; 5DFAH shows the key in Register A if it is 20H or above; 5DFDH shows it in any case. The echo goes down column 6 of the display (54B0H, from 3C06H); when it would go below the last row the key becomes 00H, which no command accepts. 5E19H reads two hexadecimal digits into Register Pair DE (5E1CH with the first key already in Register A) and returns the CARRY FLAG for a key that is not a digit. 5E2EH and 5E33H read a byte the same way and then the key after it; 5E37H reads that key: the Z FLAG for ENTER, the NZ FLAG for a comma, the CARRY FLAG for anything else. Register Pair HL and Register Pair BC are kept.

5E49H - DPWE: Display Password Encode

Asks PASSWORD?, pads the answer to 8 characters with spaces and encodes it the way the DOS stores a password code in a directory entry (the same steps as SYS2's encoding routine): Register Pair DE starts at FFFFH and every character, from the last to the first, is mixed into it. The code is shown as four hexadecimal digits, low byte first, as it is in the directory entry, and then FUNCTION COMPLETED.

5EA0H - DNTH: Display Name/Type Hash Code

Asks FILE NAME? (up to 8 characters) and FILE TYPE? (up to 3), both padded with spaces, at 5440H-5447H and 5448H-544AH. The 11 characters are XORed together with a left rotation after each; a result of 00H becomes 01H. This is the byte the directory's hash index sector holds for the file. It is written over 5440H (the address the dispatcher left on the stack) and shown as two hexadecimal digits, then FUNCTION COMPLETED.

5EDFH - RRT: Read Raw Track

Not in the menu. Asks the drive and relative sector, reads that sector so that the head is on its track, and then reads the whole track with the controller's READ TRACK command (E4H) into memory from 7000H, interrupts off. The result is shown as MAIN MEMORY RANGE 7000H- xxxxH (the last byte stored). Read errors 03H-07H of the sector read are ignored; a controller status with any of bits 7-3 set is reported as DOS error (bit number + 1). Refused under DOS-CALL (550BH).

5F85H - Controller Helpers

5F85H-5FA1H is a wait loop no instruction calls: it reads the controller status until it is not busy (returning Register A = 00H), sending FORCE INTERRUPT when the drive is not ready and selecting the drive again otherwise. 5FA2H writes the select latch value at 4309H to 37E1H. 5FA9H waits a short moment (A counts 6 down) and returns the controller status at 37ECH in Register A.

5FB2H - Show the Page

5FB2H also starts the key echo at 3C06H; 5FB8H (used by the printing at 613AH) only shows. The screen is cleared and the 256 bytes at 5495H are written straight into the display memory as 16 rows of 16 bytes: columns 4-5 the offset within the page (columns 2-5 the address for DM and DMDB), column 6 the echo column, columns 8-47 the bytes in eight groups of two, columns 48-63 the bytes as characters (21H-5FH, or 21H-7FH with option AI; others as a period). At the left of rows 0-2 DRV and the drive in decimal and hexadecimal are shown; for a disk sector DRS (relative sector within the drive) at row 4, TRK at row 8 and TRS (sector within the track) at row 12; for DFS the drive sector DRS (found through the file's extents) and FRS (the file sector) at row 12. DM shows nothing there, DMDB only MD. The status character at 5494H is shown at row 15, column 1. Register Pair BC is kept.

60ECH - Show a Label and a Number

Writes the three characters at Register Pair BC at the display address Register Pair DE, Register Pair HL in decimal (without leading zeros) one row below, and in hexadecimal with H two rows below.

6111H - Copy Direction

Called by CDS and CDD with Register Pair DE = the number of sectors the copy spans, Register B = the source offset and Register C = the destination offset. On the same drive (5499H = 549AH) bit 7 of 5493H is set, so the copy runs backwards, when the destination starts after the source and no later than the source's end, or in the same sector at a higher offset.

613AH - Print the Page

Shows the page (5FB8H) and sends the first Register C rows of the display to the printer, 64 characters each (codes below 20H as 40H-5FH). After each row the keyboard is checked: H ends with FUNCTION TERMINATED BY OPERATOR, P waits for ENTER. Two carriage returns end the page and the output goes back to the display.

617BH - DMDB: Read a Page From the Dump

The page at 54B4H is found in the file (61BFH): file byte = address - base + 2. Bytes of the page below the dump's base are filled with FFH (the page shown then starts at the base's page). The bytes are read one at a time with ROM 0013H through the FCB into 5300H; at the end of the file the rest is filled with FFH and PARTIAL BLOCK DUE TO EOF is shown. A page that starts after the end gives SOURCE SECTOR OUT OF RANGE; other errors are displayed and the menu shown.

61EAH - Hexadecimal Digits and Keyboard

61EAH writes Register Pair DE as four hexadecimal digits at Register Pair HL, 61EFH writes Register A as two; Register Pair HL ends after them. 6205H scans the keyboard with ROM 002BH (Register A = 00H if no key), 620BH waits for a key with ROM 0049H; both keep Register Pair DE and turn a lower case letter into upper case (6210H).

6219H - Messages and Questions

6219H (called by no instruction) clears the screen and shows a message with three carriage returns. 6224H shows the message at Register Pair HL and asks SURE YOU WANT TO DO THIS??? (Y OR N); N goes back to the menu. 6231H asks the question at Register Pair HL until exactly one character, Y or N, is typed: Z for N, NZ for Y. 6242H switches to the display first; 6245H shows a message and a carriage return; 6248H outputs one carriage return, 624AH Register B of them. 6252H (called by no instruction) switches to the display and goes into 6255H.

6255H - Display a Message

Messages are byte strings ended by 03H. Bytes below 60H are output as they are, except 08H, which means that the next word gets no space before it. Bytes 60H-96H are words from the list after 696BH (word number = byte - 5FH), bytes 97H-DDH words from the list after 6A23H (byte - 96H); each word ends with a byte that has bit 7 set. A word gets a space before it when it follows another word, unless its first byte is 08H. Register Pair HL returns at the 03H; Register Pair BC is kept.

62A7H - Output Characters

62A7H clears the screen (1CH home, 1FH clear to the end of the frame). 62AEH and 62B2H (called by no instruction) output 0EH and 0FH, the cursor on and off codes. 62B6H outputs 1CH. 62BAH outputs Register B characters from Register Pair HL; 62C2H (called by no instruction) one character from Register Pair HL; 62C6H a space. 62C8H outputs Register A to the display or the printer and keeps the column count at 5483H: a printable character uses a column and a full line is ended; 08H gives one back; 1CH-1FH start the line again; 0AH-0DH end the line (an empty line gets a space first), count the printed lines and, if BREAK is held, wait until ENTER. All registers are kept.

6327H - Tab and Line Input

6327H (called by no instruction) outputs spaces up to column Register B of the line. 6339H asks a question and reads up to Register B characters into 5440H, 633CH into Register Pair DE. 6345H shows a message and waits until ENTER alone is typed. 634EH shows a question and reads up to 64 characters into 5440H. The lines are read with ROM 0040H and turned into upper case; they return Register Pair HL = the line, Register B = the characters typed, Register A = the first character and the Z FLAG for an empty line.

636AH - Output Device Selection

6374H sends the output to the display, 6379H to the printer. Both first end a line that is not empty, put the JR displacement at 63ECH (22H skips the printer code, 00H runs it) and take the line width from 5485H (64) or 5486H (132). 636AH (called by no instruction) also clears the echo flag 5480H; 639FH and 63A8H (called by no instruction) set and clear its bit 6; 63AFH returns the Z FLAG at the top of a printed page. Register A is kept.

63B5H - After a Carriage Return

On the printer the lines left on the page at 5482H are counted down; at 0 six more carriage returns are printed if 5481H is not 00H, and the count starts again at 60. Then the columns left are set to the line width. 63DDH (called by no instruction) prints carriage returns until the top of a page, at most Register C of them.

63E8H - Send a Character

6427H saves Register Pair HL, Register Pair DE, Register Pair BC, Index Register IX and Index Register IY and goes on at 63EBH. The JR there has the displacement set by 638CH: 22H goes to the display code at 640FH, 00H runs the printer code at 63EDH first. The printer gets codes 0AH-0DH and 20H and above through ROM 003BH; codes above option AX (4370H) become a period, other control codes are dropped. Printed output also goes to the display when bit 6 of 5480H is set. The display code (ROM 0033H) leaves out the carriage return after a line of exactly 64 characters, because the display has already moved to the next line.

644CH - Read and Write a Sector

644CH reads with bit 6 of 5493H set (no retry question). 6457H reads the sector at the FCB's NEXT with SYS0 4436H; 6474H writes it with SYS0 443CH (write with verify), setting FCB bit 0 for a read protected write when 5494H is P and refusing a sector that was not read (E). 6497H prepares both: bit 7 of 5491H = write, FCB byte 1 bit 7 cleared, the byte within the sector 00H, and the sector number copied to 54A6H; it puts the return address in the JP at 64B9H, so a retry (64B3H) runs the DOS call again. A read sets 5494H to P (error 06H) or a space. The registers are kept; Z = done, NZ = skipped.

6497H - Prepare the FCB for a Read or Write

Called by 6457H and 6474H with Register A = 00H (read) or 80H (write). The return address goes into the JP at 64B9H and the caller's Register Pair HL and Register Pair DE stay on the stack for 6471H. Returns (through that JP) with Register Pair DE = 5400H and Register Pair HL = the sector at NEXT.

64BCH - Disk Errors

Entered with the flags of a DOS call. Z (no error) returns Register A = 00H. Error 06H (read protected) returns the Z FLAG. Otherwise the screen is cleared, the location shown (65D0H), and SOURCE SECTOR READ ERROR, DESTINATION SECTOR WRITE ERROR or DESTINATION SECTOR VERIFY ERROR (a write with a code below 09H, which comes from the verify read); then the error's text from the table at 6BEDH, or for DFS and DMDB the DOS message (4409H), or SYSTEM ERROR CODE n. VDS, ZDS and CDS ask R (retry, CARRY FLAG), S (skip, NZ FLAG) or X (end); CDD and RRT go back to the menu; a display function shows BUFFER MAY CONTAIN SOME OR ALL OF SECTOR DATA and the display mode. With bit 6 of 5493H the routine returns NZ. A read error sets 5494H to E.

6573H - Ending a Function

6573H (called by no instruction) shows the message at Register Pair DE as below. 6576H and 6578H display a DOS error (Register A, 01H at 6576H) through SYS0 4409H. 657FH switches to the display and shows the message at Register Pair HL; 6582H shows PRESS 'ENTER' TO RETURN TO MENU and goes back to the menu after ENTER. The entries from 658EH load their message and go there; 6598H, 65A0H and 65A5H (parameter errors) return the CARRY FLAG instead.

65D0H - Show the Location of a Sector

Displays DRIVE d, dH and then, for a file (DFS, DMDB), FRS n, nH; otherwise DRS n, nH TRACK t, tH SECTOR s, sH, from the sector at 54A6H and the sectors per track at 549BH. 660DH shows the label at Register Pair HL and the number in Register Pair DE in decimal and hexadecimal (with a 0 before a hexadecimal number that starts with a letter). 6649H outputs Register A as two hexadecimal digits; 665BH outputs Register Pair DE as four with H and two spaces.

6665H - Hexadecimal Without Leading Zeros

6665H writes Register Pair DE at Register Pair HL: four digits when Register D is not 00H, two when Register E is 10H or more, otherwise one. 6670H writes Register A with one or two digits, 6674H always two, 667DH one. Register Pair HL ends after the digits.

668AH - Copy, Compare and Character Tests

668AH copies Register B bytes from Register Pair HL to Register Pair DE. 6691H-66D4H, called by no instruction, are compares of register pairs (6691H HL with DE, 6697H HL with BC and then DE with HL, 66A2H DE with BC and then BC with HL, 66ADH BC with DE), a compare of Register B bytes at Register Pair DE and Register Pair HL (66B3H) and letter tests (66BBH, 66C3H, 66CBH). 66D5H returns the CARRY FLAG when Register A is a decimal digit (it is also the end of 66C3H and 66CBH).

66DCH - The Count and Offset Questions

66DCH asks SECTOR COUNT?, 66E1H BYTE COUNT?, both until 677BH accepts a count from 1 to 65535 (stored at 54ACH). 66EFH asks BYTE OFFSET WITHIN SECTOR? until 66FBH accepts a value below 256 (stored at 54AEH). An X as the answer goes back to the menu (681BH).

670FH - Parameters: Drive, Track, Sector, Address, Count

Each takes one parameter from the answer at Register Pair HL (67EDH), checks it, stores it and returns the NO CARRY FLAG with the Z FLAG for the last parameter or the NZ FLAG when more follow; a bad value displays its BAD/ILLEGAL message and returns the CARRY FLAG. 670FH: the drive, stored at 5406H and 5499H, then 67B5H checks the diskette. 6732H: the track, below 430DH, to 549EH. 6751H: the sector, below 549BH, to 54A0H. 6770H: a memory address in Register Pair DE. 677BH: a count from 1 up, to 54ACH. 678FH shows a message and asks DRIVE AND RELATIVE-SECTOR-WITHIN-DRIVE #'S? (6792H only asks); 679EH takes the relative sector to 54A2H.

67B5H - Check the Drive and Read Its Sizes

Checks the drive at 5406H with SYS0 445EH (an error is displayed through 4409H and the menu shown) and copies the drive's sizes: 549BH sectors per track (430EH), 549CH granules per lump (430FH), 54A8H = tracks (430DH) x sectors per track. All registers are kept.

67E5H - Take a Number From the Answer

67E5H takes the last parameter (TOO MANY PARAMETERS if more follow). 67EDH takes one: ENTER gives TOO FEW PARAMETERS, a comma MISSING IMBEDDED PARAMETER (both with the CARRY FLAG). A number is decimal, or hexadecimal when it ends in H (a digit A-H after the decimal digits starts the hexadecimal reading). It must be followed by ENTER (Z FLAG) or a comma (NZ FLAG, Register Pair HL after it); X goes back to the menu; anything else returns the CARRY FLAG. The value is in Register Pair DE.

687BH - Multiply and Divide

687BH multiplies Register L by Register A, 687DH Register Pair HL by Register A; the product is in Register Pair HL, Register Pair DE and Register Pair BC are kept. 6896H divides Register Pair HL by Register A: the quotient in Register Pair HL, the remainder in Register A.

68A6H - Decimal Numbers

68AFH writes Register Pair DE as five decimal digits at 5487H-548BH (68D1H), replaces leading zeros by spaces and returns Register Pair HL = the first digit shown, Register B = the digits from there, Register Pair DE = the caller's Register Pair HL. 68A6H takes Register A and 68A7H Register E as the number; 68ABH (called by no instruction) the word at Register Pair HL; 68C5H (called by no instruction) outputs the five digits; 68D0H (called by no instruction) takes the number in Register Pair HL.

68F6H - Powers of Ten and Display Labels

Data. 68F6H holds minus 10000, 1000, 100 and 10 for the decimal conversion at 68D1H. 68FEH-690CH are the three-letter labels the display shows at the left (60ECH).

690DH - Command Table

Data, searched by 54EDH. Each entry is the command name, the flags byte (bit 7 set, which ends the name; the rest goes to 5491H), the second flags byte (to 5492H) and the handler address. A 00H in place of a name ends the table.

696BH - Word List 1

Data, read by the message routine 6255H. 696BH is a byte with bit 7 set that the search for word 1 passes over; then each word ends with a byte with bit 7 set, and a 00H ends the list. Message bytes 60H-96H stand for these words in order.

6A23H - Word List 2

Data, read by the message routine 6255H. 6A23H is a byte with bit 7 set that the search for word 1 passes over; then each word ends with a byte with bit 7 set, and a 00H ends the list. Message bytes 97H-DDH stand for these words in order.

6BEDH - Disk Error Table

Data, searched by 64FAH. Each group is the error codes it covers, 00H, and the message (ended by 03H); a 00H in place of the first code ends the table. Codes not in the table are reported by the DOS (DFS, DMDB) or as SYSTEM ERROR CODE n.

6C2DH - Messages

Data, displayed by 6255H: bytes below 60H as they are (08H: no space before the next word), 60H-DDH words from the two lists, 03H the end. Each row gives the text as it is displayed and the instructions that use it.

6F00H - Unused Bytes

The end of the file: 254 zero bytes that no instruction reads.