TRS-80 DOS - NEWDOS/80 v2.0 for the Model I - SYS7/SYS Disassembled

SYS7/SYS

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NEWDOS/80 v2.0 SYS7/SYS Disassembly - SYSTEM, HIMEM, PDRIVE, AUTO, ATTRIB, PROT, DUMP, PURGE, TIME and DATE (Model I)

SYS7/SYS holds ten library commands. It loads into the overlay area at 4D00H-51E7H (1,256 bytes in five load records, transfer address 4D00H). SYS1 calls it with LD A,E9H / RST 28H (function 7) and the sub-function from its command table in Register C; the SYS0 dispatcher (4BC2H) loads SYS7 when 4317H does not already hold its number (09H). SYSTEM, PDRIVE and PURGE are only started here: SYS7 reads the drive and checks the diskette password, and passes the rest of the command line to SYS17, SYS16 or SYS3.

The page shows every byte of the file once, in address order.

Sub-Functions of Code E9H

Parameters and Passwords

DUMP

Variables and Work Areas

4D00H - Function Dispatcher

SYS7 is entered by the SYS0 RST 28H dispatcher (4BC2H) with Register A = the RST 28H code. Only function 7 (E9H) exists; Register C is the sub-function from SYS1's command table (4F58H), and Register Pair HL points to the rest of the command line. Sub-functions: 1 SYSTEM, 2 HIMEM, 3 PDRIVE, 4 AUTO, 5 ATTRIB, 6 PROT, 7 DUMP, 8 the second half of DUMP (reached only through the 49D3H chain at 5137H), 9 PURGE, 0AH TIME, 0BH DATE. Anything else returns error 2AH.

4D32H - Error 2AH, and the TIME and DATE Commands

4D32H is reached from the dispatcher for a code that is not E9H, and falls through for sub-function 0BH (DATE). TIME and DATE without a parameter display the clock or date as HH:MM:SS or MM/DD/YY (with the SYS0 routine at 44ACH); with a parameter they set it (4DA7H).

4D4CH - Unreferenced Error Exit

Nothing in SYS7 or in the other overlays reaches 4D4CH.

4D50H - Error Exits and the End of the Command

4D50H returns error 20H (from 4EA2H). 4D54H accepts the end of the line or a separator (comma or spaces; NZ, with HL past it) and otherwise gives error 34H; 4D58H accepts only the end of the line. 4D5EH is the common error exit through SYS0 4409H, which displays the error.

4D61H - SYSTEM, PDRIVE and PURGE Commands

These three only read [password]:d or d and check the diskette password (4E89H), then pass the rest of the line to another overlay with Register B = the drive: SYSTEM to SYS17 function 1 (code 33H), PDRIVE to SYS16 function 1 (code 32H), PURGE to SYS3 function 7 sub-function 6 (code E5H, C = 06H).

4D76H - HIMEM Command

Without a parameter HIMEM displays the address in 4049H (HIMEM) as four hexadecimal digits. With one it stores the value, which may be decimal or hexadecimal with a trailing H (4F9EH), must be 7000H or higher, and is lowered to the top of memory found at reset (43A9H) if it is above it.

4DA7H - TIME and DATE: Set the Clock or Date

Three fields of two decimal digits, separated by the character stored at 4DCBH (: or /), are stored downward from DE: hours, minutes, seconds at 4043H-4041H, or month, day, year at 4046H-4044H. The values are not range-checked. Interrupts are off while the fields are stored, so the clock does not change in between. A field that is not two digits, or a wrong separator, gives error 2FH; anything but the end of the line after the third field gives error 34H (already stored).

4DD4H - AUTO Command

Stores the rest of the command line, up to and including its carriage return, in bytes E0H-FFH of the GAT of drive 0 (the command run at reset). At most 31 characters; longer text gives error 2FH and nothing is written. AUTO without text stores only the carriage return (no AUTO command).

4DF3H - ATTRIB Command

SYS1 has opened the file (FCB at DE) and left the command line pointer on the stack. The file must have been opened with full access (the update password, or any password when option AA is off), otherwise error 19H. Its FPDE is read and changed by the keywords in the table at 504DH, separated by commas or spaces; then the directory sector is written back. Keywords: INV and VIS (invisible bit), PROT=level (508CH), ACC=password, UPD=password, ASE=Y/N, ASC=Y/N, UDF=Y/N and LRL=n.

4E10H - ATTRIB LRL=

LRL=n sets the record length (FPDE byte 4) to n, 1-256 (256 is stored as 0). Other values give error 2FH.

4E23H - ATTRIB UDF=, ASE= and ASC=

Each changes one bit of FPDE byte 1: UDF (bit 5, the file has been updated) is set by Y and cleared by N; ASE (bit 7, no extension) and ASC (bit 6, no space release at CLOSE) are cleared by Y and set by N. Anything but Y or N gives error 2FH.

4E4DH - ATTRIB INV, VIS and PROT=

INV sets and VIS clears bit 3 of FPDE byte 0 (invisible). PROT=level stores the access level (LOCK 7, EXEC 6, READ 5, WRITE 4, RENAME or NAME 2, KILL 1, FULL 0; table 508CH) in bits 0-2 of byte 0. 4E5BH then continues with the next keyword, or at the end of the line writes the directory sector.

4E71H - ATTRIB ACC= and UPD=

ACC=password stores the password's code at FPDE bytes 18-19 (access password), UPD=password at bytes 16-17 (update password). A blank password gives the code 4296H.

4E89H - Read a Drive and Check the Diskette Password

Used by PROT, SYSTEM, PDRIVE and PURGE. The text is password:d, :d or d. The drive is selected (47ECH, error 08H if there is no diskette) and its GAT read into 4200H. If a password was given and it is not the diskette's password (GAT CEH-CFH), the result is error 37H, but only when option AA (436CH bit 7) is on. Returns with HL after the drive number.

4EC5H - PROT Command

PROT [password]:d,keyword,... changes the diskette's GAT: PW=password (new diskette password), NAME=name and DATE=date (8 characters each), and applies LOCK, UNLOCK and RUF to all its files (4F09H). The keywords are in the table at 50C0H.

4ED1H - PROT DATE= and NAME=

Copies up to 8 characters, up to a comma, space or the end of the line, to GAT bytes D8H-DFH (DATE=) or D0H-D7H (NAME=), padded with spaces.

4EEFH - PROT RUF, UNLOCK and LOCK

These only set a bit in the operand at 4F13H; the files are changed after the last keyword (4F12H). Bit 2 RUF, bit 0 UNLOCK, bit 1 LOCK.

4F02H - PROT PW=

PW=password stores the new password's code in GAT bytes CEH-CFH. A later LOCK uses the new code.

4F09H - PROT: Next Keyword, Then Change the Files

After the last keyword the GAT is written back. Then, if LOCK, UNLOCK or RUF was given, every FDE sector of the directory (8 plus the extra sectors counted in HIT byte 1FH) is read and each FPDE in use is changed: RUF clears the updated bit (byte 1 bit 5) of every file; LOCK sets both password codes of every file that is neither a system file nor invisible to the diskette password, UNLOCK sets them to the blank code 4296H. Each sector is written back.

4F6BH - A Separator Must Follow

Steps HL over a comma or spaces; any other character (or the end of the line) gives error 34H.

4F71H - Find a Keyword

4F71H searches a table of keyword entries (the name, 00H, and a two-byte handler address) and jumps to the handler of the keyword at HL, with HL past the keyword. 4F7DH does the search for any table with D bytes after each name and returns BC pointing to them. No match gives error 34H. The text only has to start with the keyword.

4F93H - Read an Optional Number

4F93H: at the end of the line RETURN with DE unchanged; after a separator read a number. 4F99H: a separator and a number must follow. 4F9EH reads a number: decimal, or hexadecimal with a trailing H (A-F and H after decimal digits restart the reading as hexadecimal). Returns DE = the value; no digit, a missing H or a value over FFFFH gives error 2FH.

4FF5H - Read a Password and Encode It

4FFEH copies a name of up to 8 characters (a letter, then letters and digits) to 51E8H-51EFH, padded with spaces, and leaves HL after it. If the text does not start with a letter nothing is taken and the name is blank. 501CH then encodes the 8 characters into a 16-bit code in DE with the same algorithm as SYS2 5155H (a blank name gives 4296H). The buffer is left blank.

504DH - ATTRIB Keyword Table

Searched by 4F71H: the keyword, 00H, and the handler address.

508CH - Access Level Table

Searched by 4E68H for PROT=: the name, 00H, and the level for FPDE byte 0 bits 0-2.

50C0H - PROT Keyword Table

Searched by 4F71H: the keyword, 00H, and the handler address.

50EDH - DUMP Command

DUMP filespec,start,end[,entry[,load]] writes memory start-end to the file (opened by SYS1 in the FCB at 4480H) in load module format. Numbers are decimal or hexadecimal with H. The entry address defaults to 402DH (DOS READY); the load address, where the data will be loaded, defaults to start. With entry = FFFFH the file is written without records instead (only the load address as two bytes, then the data) and no load address is read. The file's sector buffer is set to 4D61H, inside SYS7 itself (over the code for SYSTEM to ATTRIB, which DUMP does not need). Before the dump one sector is written at sector (count + 4) / 252 of the file, so that all the space the file needs is allocated at once; the 49D3H chain then brings DUMP back as sub-function 8.

5142H - DUMP, Sub-Function 8: Write the Data

Entered through 49D3H with DE = the FCB and the values pushed at 5116H-511DH on the stack. The file is rewound and the bytes are sent one at a time through the ROM output routine at 001BH with DE = the FCB (SYS0 4ADBH writes them to the file). Load module records are type 01H, a length byte (the data length plus 2; 00H means 256), the two-byte load address (51B4H translates it) and up to 254 data bytes; the last record is the transfer record 02H 02H and the entry address. Finally the file is rewound again and closed through SYS0 4428H.

51ACH - DUMP: Write a Record Header and an Address

51ACH writes Register B (the type) and Register C (the length). 51B4H writes the address in DE as two bytes, translated when it lies between start and end: DE - start + load. 51D3H writes the byte in Register A through ROM 001BH with the FCB in DE' and ends DUMP with the error on a write error.

51DCH - Unused Bytes