DOSPLUS 3.5 for the Model III - SYS13/SYS Disassembled

SYS13/SYS

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DOSPLUS 3.5 SYS13/SYS Disassembly - The Library Commands DO, FORMS and RS232 (Model III)

SYS13/SYS is the fifth of the high overlays: it loads at 5200H and holds three library commands, routines 3 to 5 of its table at 5200H with the request codes C3H to C5H: DO, FORMS and RS232. CMNDI@ takes the codes from SYS1/SYS's table of the library commands and passes them to the overlay request handler, which loads SYS13/SYS and calls the routine with Register Pair HL at the rest of the command line. No file of the diskette requests routine 2 (C2H). The file is a load module of 5 blocks, 1152 bytes, from 5200H to 567FH, with the transfer address 5200H and no gaps; the work area after the file starts at 5680H.

The Parts of SYS13/SYS

DO

DO (520AH) takes the file and the parameters HIGH and BREAK through EVAL@ with its block at 5582H; all three field blocks are the one at 5680H, and a missing field or a field without a name (a drive or a device) is error 2FH. HIGH, by default HMEM$ as it is, becomes HMEM$ (4411H). BREAK, by default Y, clears bit 0 of SFLAG1$ (4297H), so that the BREAK key works, and BREAK=N sets it. Unless bit 6 of SFLAG1$ shows that a DO already took its memory, DO sets that bit and takes the 288 bytes below HMEM$: HMEM$ is lowered by 0120H, and the file control block starts at the new HMEM$ plus 1, followed by its 256 byte buffer; its address goes to DODCB$ (42A9H). FSPEC@ puts the file into that block, FEXT@ gives it the extension TXT when it has none, OPEN@ opens it, and bit 5 of SFLAG1$ is set: a DO file is running.

FORMS

FORMS (5285H) works on the control block of @PR (device 2, from LOCDCB%): +03H the page length (PAGE), +07H the lines used on a page (LINES), +06H the width (WIDTH). Without parameters it shows $02 @PR Page=n,Lines=n,Width=n (52FCH), the name taken from @PR's entry of SYS0/SYS's DCB table (44C5H). With parameters, PARAM@ takes PAGE, LINES, WIDTH, TOP and CODE through the table at 559EH into words at 5680H (CODE into an operand of FORMS); an unknown parameter is error 2EH and a value above 255 error 2DH. The three values go back into the control block; then CODE sends its high byte and then its low byte to the printer through the ROM's 003BH, each only when it is not 00H, and TOP sends a form feed (0CH).

RS232

RS232 (533DH) keeps the settings of the RS-232 interface in the ROM's RS-232 initialisation control block at 41F5H: 41F8H the baud rate byte (bits 7-4 the sending rate, bits 3-0 the receiving rate, each an index into the 16 rates at 5562H), 41F9H the control byte and 41FAH the wait switch (00H no wait). Without parameters it shows $03 @RS Baud=n,Word=n,Stops=n,Parity=x and the marks ,Wait ,BRK ,DTR ,RTS (5348H); the baud rate shown is the receiving one. In both cases the interface is then set up by the ROM's RS-232 initialisation at 005AH (54ECH), which takes its values from 41F8H-41FAH.

With parameters (53EEH) PARAM@ takes BAUD, WORD, STOPS, EVEN, ODD, PARITY, DTR, RTS, BREAK and WAIT through the table at 55C7H, each value into the operand of an instruction further on: BAUD's operand is first set to 0000H and the other nine to 80H in their low byte, the mark of a parameter not given. BAUD must be one of the 16 rates and sets both halves of the baud rate byte; WORD (5-8) sets bits 6-5 of the control byte (00 for 5 bits, 10 for 6, 01 for 7, 11 for 8), STOPS (1 or 2) bit 4, PARITY=N bit 3 (no parity), EVEN bit 7 (even parity); DTR=N sets bit 1, RTS=N bit 0 and BREAK=N bit 2, and each of them given as Y clears its bit. A rate not in the table, a word length outside 5-8, STOPS 3 or more, or EVEN and ODD with the same value is error 2DH; an unknown parameter is error 2EH. WAIT stores its low byte into 41FAH when it is given.

Differences from the Manual

CODE sends the high byte of its value first and the low byte second (FORMS (CODE=0F1BH) sends 0FH, then 1BH); the manual says the last byte given, 1BH, is sent first. Only EVEN decides the parity sense: ODD=N alone gives odd parity, where the manual says ODD=N is the same as EVEN=Y, and ODD=Y with EVEN=Y, or ODD=N with EVEN=N, is refused. STOPS=0 is not refused: 0 less 1 gives FFH, so every bit of the control byte is set. RS232 also takes a parameter WAIT, which the manual does not list (on the Model I it has no effect; on the Model III it is the ROM's wait switch). DO's BREAK sets the BREAK key flag of SFLAG1$ itself, for the system, and DO without BREAK turns the BREAK key on even after BREAK OFF; SYS13/SYS does not keep the old setting. The entry 5552H that posts error 2CH (Illegal filespec) is reached by nothing.

The bits DOSPLUS gives the control lines: the DTR parameter sets or clears bit 1 of the control byte and RTS bit 0, and the display follows the same bits. The ports page of this site gives bit 0 as DTR and bit 1 as RTS; the page follows the bytes.

Differences from the Model I

The code is the Model I SYS13/SYS with the Model III addresses of SYS0/SYS (HMEM$ 4411H, SFLAG1$ 4297H, DODCB$ 42A9H, FEXT@ 444BH, PARAM@ 4454H, LOCDCB% 44A0H, the names of @PR and @RS in the DCB table 44C5H and 44D0H) except in RS232. Index Register IX points to 41F5H, the ROM's RS-232 initialisation control block, so the baud rate byte is IX+03H (41F8H) and the control byte IX+04H (41F9H) where the Model I has IX+00H (4305H) and IX+01H (4306H). The display shows ,Wait when IX+05H (41FAH) is not 00H (ten bytes more at 53DCH-53E5H), and the end of RS232 stores WAIT into 41FAH and jumps to the ROM's 005AH instead of writing to ports E8H, E9H and EAH itself (54E4H-54EEH, three bytes less). So the code from 53E6H to 54E3H is ten bytes higher than on the Model I, and the code and data from 54EFH on seven bytes higher.

5200H - The Routine Table

Data: SYS13/SYS's table of routines 2-5, one word each, used by SYS0/SYS's overlay request handler (its 49D3H-49E6H) for the request codes C2H-C5H. CMNDI@ takes the codes of the library commands from SYS1/SYS's table: DO C3H (51C7H), FORMS C4H (51CCH), RS232 C5H (51D8H). No file of the diskette requests C2H.

5208H - Routine 2

Nothing to do when SYS0/SYS's record locator brings SYS13/SYS back.

520AH - DO

Routine 3, entered from CMNDI@ through the overlay request handler with Register Pair HL at the rest of the command line. EVAL@ takes the file and the parameters HIGH (the top of memory, by default HMEM$ as it is) and BREAK (by default Y) with the block at 5582H; a missing field, or a field that is a drive or a device, is error 2FH. HMEM$ is set to HIGH, and BREAK=N sets bit 0 of SFLAG1$ (the BREAK key is disabled) while BREAK=Y clears it. The first DO (bit 6 of SFLAG1$ clear) sets that bit and takes 288 bytes below HMEM$: HMEM$ is lowered by 0120H and the file control block starts at the new HMEM$ plus 1, followed by its 256 byte buffer; the address goes to DODCB$ (42A9H). A DO while that memory is taken uses the same block. The file is opened (default extension TXT) and bit 5 of SFLAG1$ is set: a DO file is running. Register B is not loaded before OPEN@.

5285H - FORMS

Routine 4, entered from CMNDI@ through the overlay request handler with Register Pair HL at the rest of the command line. Index Register IX gets the control block of @PR (device 2) from LOCDCB%: +03H the page length (PAGE), +07H the lines used on a page (LINES), +06H the width (WIDTH). Without parameters the settings are shown (52FCH). Otherwise the three values are copied as words into 5680H-5685H (Index Register IY), PARAM@ takes PAGE, LINES, WIDTH, TOP and CODE with the table at 559EH (an unknown parameter is error 2EH), a value above 255 is error 2DH, and the values go back into the control block. CODE then sends its high byte and then its low byte to the printer, each only when it is not 00H, and TOP sends a form feed (0CH).

52FCH - Show the Settings of @PR

One line on the display: $02 @PR Page=n,Lines=n,Width=n, the name taken from @PR's entry of the DCB table (44C5H), the numbers in decimal from +03H, +07H and +06H of the control block at Index Register IX.

5338H - Show a Byte in Decimal

Shows the number in Register E (0-255) on the display in decimal without leading zeros.

533DH - RS232

Routine 5, entered from CMNDI@ through the overlay request handler with Register Pair HL at the rest of the command line. Index Register IX points to 41F5H, the ROM's RS-232 initialisation control block: +03H (41F8H) the baud rate byte (bits 7-4 the sending rate, bits 3-0 the receiving rate, both an index into the table at 5562H), +04H (41F9H) the control byte, +05H (41FAH) the wait switch (00H no wait). Without parameters the settings are shown and the interface is set up again (53EBH); with parameters they are changed first (53EEH). Either way the ROM's RS-232 initialisation at 005AH sets up the interface from them.

5348H - Show the RS-232 Settings

One line on the display: $03 @RS Baud=n,Word=n,Stops=n,Parity=None, Even or Odd, then ,Wait when the wait switch is not 00H, ,BRK when a break is sent (bit 2 clear), ,DTR when bit 1 is clear and ,RTS when bit 0 is clear; then the interface is set up by the ROM (54ECH).

53EEH - Change the RS-232 Settings

PARAM@ takes BAUD, WORD, STOPS, EVEN, ODD, PARITY, DTR, RTS, BREAK and WAIT with the table at 55C7H (an unknown parameter is error 2EH). Each value goes into the operand of an LD DE,0000H (EVEN's into that of an LD BC,0000H) below; BAUD's operand is first set to 0000H and the other nine to 80H in their low byte, the mark of a parameter not given. Each parameter given then changes its bits of the control byte, and a wrong value is error 2DH.

5412H - BAUD

The value must be one of the 16 rates of the table at 5562H (else error 2DH); its index n (0-15) is stored as nnH, the same rate for sending and receiving, into the baud rate byte. 0 or no BAUD keeps the byte as it is.

543DH - WORD

The control byte is built in Register L from its old value. WORD must be 5, 6, 7 or 8 (else error 2DH) and sets bits 6-5: 00 for 5, 10 for 6, 01 for 7, 11 for 8.

5463H - STOPS

STOPS 1 clears bit 4 and STOPS 2 sets it; a value of 3 or more is error 2DH. STOPS=0 is not refused: 0 less 1 is FFH, so every bit of the control byte is set (8 bits, two stop bits, no parity, even, no break, DTR and RTS off).

5480H - PARITY

PARITY=Y (or PARITY alone) clears bit 3, parity used; PARITY=N sets it, no parity.

5491H - EVEN and ODD

Bit 7 is set for even parity and cleared for odd. EVEN and ODD with the same value (both given as Y, or both as N) are error 2DH. Otherwise bit 6 of EVEN's value decides alone: EVEN=Y gives even, EVEN=N or no EVEN gives odd, so ODD=N alone gives odd parity, where the manual says it is the same as EVEN=Y.

54ABH - DTR, RTS and BREAK

Each switch given as Y (or alone) clears its bit and as N sets it: DTR bit 1, RTS bit 0, BREAK bit 2. WAIT is taken into the operand at 54E2H and stored into the wait switch (41FAH) when it is given (54E4H).

54E4H - WAIT and the Interface

WAIT given stores its low byte into the wait switch at 41FAH (00H no wait); then the ROM's RS-232 initialisation at 005AH sets up the interface from 41F8H-41FAH and returns to CMNDI@.

54EFH - Show a Number in Decimal

Shows the number in Register Pair DE (0-65535) on the display in decimal without leading zeros: 5504H puts the digits at 5680H, and DSPLY@ shows them.

54F9H - The End of the Line

Tests the character at Register Pair HL: a control code (below 20H) or a semicolon is the end of the line, returned with the C FLAG and Register Pair HL unchanged; any other character is returned in Register A with the NC FLAG and Register Pair HL past it.

5504H - Decimal Digits

Puts the number in Register Pair DE (0-65535) at Register Pair HL as decimal digits without leading zeros (at least one digit), ended by 03H, and returns Register Pair HL at the digits and Register Pair DE at the 03H. The number is turned into six BCD digits at 5680H-5682H (sixteen doublings by ADC and DAA), and the digits into ASCII at 5683H-5688H by RLD; the digits after the leading zeros are then copied to Register Pair HL, which may be 5680H itself.

5552H - The Error Exits

Four entries, each loading its error code into Register A: 5552H 2CH Illegal filespec (entered by nothing), 5555H 2FH I/o field not found, 5558H 2DH Invalid data provided, 555BH 2EH Invalid parameter. Each LD A,n after the first is the operand of an LD BC,nn entered from the entry above it. 555DH posts the error in Register A by ERROR@ with bit 6 set (no frame), and ERROR@ ends with ABORT@.

5562H - The Baud Rates

Data: the 16 baud rates RS232 accepts, one word each, in the order of their index 0-15, the value of each half of the baud rate byte.

5582H - DO's Evaluation Block

Data: the block that Index Register IX points to for EVAL@ (5217H): EVAL@'s flags, the addresses of the source, destination and wildmask blocks (all three 5680H, so the one field given lands there), and the parameter table. Each entry of the table is the name (6 characters), the address its value is stored to and a type byte.

559EH - FORMS's Parameter Table

Data: the table for PARAM@ (52BDH), eight bytes an entry: the name, then the address its value is stored to. The values of PAGE, LINES, WIDTH and TOP go into the work area at 5680H, CODE's into an operand of FORMS.

55C7H - RS232's Parameter Table

Data: the table for PARAM@ (5409H), eight bytes an entry: the name, then the address its value is stored to, each the operand of an LD DE,0000H (EVEN's of an LD BC,0000H) in RS232. The first entry that starts with an abbreviation is taken, so B is BAUD and BR is BREAK.

5618H - The Texts

Data: DO's default extension and the parts of the lines of FORMS and RS232, each ended by 03H for DSPLY@.

5680H - The Work Area

Not in the file: SYS13/SYS uses the memory after its last byte (567FH) for the field of DO's EVAL@ block, the values of FORMS, the digits of a number, and the values of HIGH and BREAK.