Routines |
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SAVE_ETC | 0605 | POP AF | Drop the address - SCAN_LOOP. | |
0606 | LD A,($5C74) | Reduce T-ADDR-lo by +E0, giving +00 for SAVE, +01 for LOAD, +02 for VERIFY and +03 for MERGE. | ||
0609 | SUB $E0 | |||
060B | LD ($5C74),A | |||
060E | CALL CLASS_0A | Pass the parameters of the 'name' to the calculator stack. | ||
0611 | CALL SYNTAX_Z | Jump forward if checking syntax. | ||
0614 | JR Z,SA_DATA | |||
0616 | LD BC,$0011 | Allow seventeen locations for the header of a SAVE (T-ADDR-lo=+00) but thirty four for the other commands. | ||
0619 | LD A,($5C74) | |||
061C | AND A | |||
061D | JR Z,SA_SPACE | |||
061F | LD C,$22 | |||
SA_SPACE | 0621 | RST $30 | The required amount of space is made in the work space. | |
0622 | PUSH DE | Copy the start address to the IX register pair. | ||
0623 | POP IX | |||
0625 | LD B,$0B | A program name can have up to ten characters but first enter eleven space characters into the prepared area. | ||
0627 | LD A," " | |||
SA_BLANK | 0629 | LD (DE),A | ||
062A | INC DE | |||
062B | DJNZ SA_BLANK | |||
062D | LD (IX+$01),$FF | A null name is +FF only. | ||
0631 | CALL STK_FETCH | The parameters of the name are fetched and its length is tested. | ||
0634 | LD HL,$FFF6 | This is '-10'. | ||
0637 | DEC BC | In effect jump forward if the length of the name is not too long (i.e. no more than ten characters). | ||
0638 | ADD HL,BC | |||
0639 | INC BC | |||
063A | JR NC,SA_NAME | |||
063C | LD A,($5C74) | But allow for the LOADing, VERIFYing and MERGEing of programs (T-ADDR-lo>+00) with 'null' names or extra long names. | ||
063F | AND A | |||
0640 | JR NZ,SA_NULL | |||
Report F - Invalid file name.
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0642 | RST $08 | Call the error handling routine. | ||
0643 | DEFB $0E | |||
Continue to handle the name of the program.
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SA_NULL | 0644 | LD A,B | Jump forward if the name has a 'null' length. | |
0645 | OR C | |||
0646 | JR Z,SA_DATA | |||
0648 | LD BC,$000A | But truncate longer names. | ||
The name is now transferred to the work space (second location onwards).
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SA_NAME | 064B | PUSH IX | Copy the start address to the HL register pair. | |
064D | POP HL | |||
064E | INC HL | Step to the second location. | ||
064F | EX DE,HL | Switch the pointers over and copy the name. | ||
0650 | LDIR | |||
The many different parameters, if any, that follow the command are now considered. Start by handling 'xxx "name" DATA'.
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SA_DATA | 0652 | RST $18 | Is the present code the token 'DATA'? | |
0653 | CP $E4 | |||
0655 | JR NZ,SA_SCR | Jump if not. | ||
0657 | LD A,($5C74) | However it is not possible to have 'MERGE name DATA' (T-ADDR-lo=+03). | ||
065A | CP $03 | |||
065C | JP Z,REPORT_C | |||
065F | RST $20 | Advance CH-ADD. | ||
0660 | CALL LOOK_VARS | Look in the variables area for the array. | ||
0663 | SET 7,C | Set bit 7 of the array's name. | ||
0665 | JR NC,SA_V_OLD | Jump if handling an existing array. | ||
0667 | LD HL,$0000 | Signal 'using a new array'. | ||
066A | LD A,($5C74) | Consider the value in T-ADDR-lo and give an error if trying to SAVE or VERIFY a new array. | ||
066D | DEC A | |||
066E | JR Z,SA_V_NEW | |||
Report 2 - Variable not found.
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0670 | RST $08 | Call the error handling routine. | ||
0671 | DEFB $01 | |||
Continue with the handling of an existing array.
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SA_V_OLD | 0672 | JP NZ,REPORT_C | Note: this fails to exclude simple strings. | |
0675 | CALL SYNTAX_Z | Jump forward if checking syntax. | ||
0678 | JR Z,SA_DATA_1 | |||
067A | INC HL | Point to the 'low length' of the variable. | ||
067B | LD A,(HL) | The low length byte goes into the work space, followed by the high length byte. | ||
067C | LD (IX+$0B),A | |||
067F | INC HL | |||
0680 | LD A,(HL) | |||
0681 | LD (IX+$0C),A | |||
0684 | INC HL | Step past the length bytes. | ||
The next part is common to both 'old' and 'new' arrays. Note: syntax path error.
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SA_V_NEW | 0685 | LD (IX+$0E),C | Copy the array's name. | |
0688 | LD A,$01 | Assume an array of numbers. | ||
068A | BIT 6,C | Jump if it is so. | ||
068C | JR Z,SA_V_TYPE | |||
068E | INC A | It is an array of characters. | ||
SA_V_TYPE | 068F | LD (IX+$00),A | Save the 'type' in the first location of the header area. | |
The last part of the statement is examined before joining the other pathways.
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SA_DATA_1 | 0692 | EX DE,HL | Save the pointer in DE. | |
0693 | RST $20 | Is the next character a ')'? | ||
0694 | CP ")" | |||
0696 | JR NZ,SA_V_OLD | Give report C if it is not. | ||
0698 | RST $20 | Advance CH-ADD. | ||
0699 | CALL CHECK_END | Move on to the next statement if checking syntax. | ||
069C | EX DE,HL | Return the pointer to the HL register pair before jumping forward. (The pointer indicates the start of an existing array's contents.) | ||
069D | JP SA_ALL | |||
Now consider 'SCREEN$'.
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SA_SCR | 06A0 | CP $AA | Is the present code the token SCREEN$? | |
06A2 | JR NZ,SA_CODE | Jump if not. | ||
06A4 | LD A,($5C74) | However it is not possible to have 'MERGE name SCREEN$' (T-ADDR-lo=+03). | ||
06A7 | CP $03 | |||
06A9 | JP Z,REPORT_C | |||
06AC | RST $20 | Advance CH-ADD. | ||
06AD | CALL CHECK_END | Move on to the next statement if checking syntax. | ||
06B0 | LD (IX+$0B),$00 | The display area and the attribute area occupy +1B00 locations and these locations start at +4000; these details are passed to the header area in the work space. | ||
06B4 | LD (IX+$0C),$1B | |||
06B8 | LD HL,$4000 | |||
06BB | LD (IX+$0D),L | |||
06BE | LD (IX+$0E),H | |||
06C1 | JR SA_TYPE_3 | Jump forward. | ||
Now consider 'CODE'.
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SA_CODE | 06C3 | CP $AF | Is the present code the token 'CODE'? | |
06C5 | JR NZ,SA_LINE | Jump if not. | ||
06C7 | LD A,($5C74) | However it is not possible to have 'MERGE name CODE' (T-ADDR-lo=+03). | ||
06CA | CP $03 | |||
06CC | JP Z,REPORT_C | |||
06CF | RST $20 | Advance CH-ADD. | ||
06D0 | CALL PR_ST_END | Jump forward if the statement has not finished. | ||
06D3 | JR NZ,SA_CODE_1 | |||
06D5 | LD A,($5C74) | However it is not possible to have 'SAVE name CODE' (T-ADDR-lo=+00) by itself. | ||
06D8 | AND A | |||
06D9 | JP Z,REPORT_C | |||
06DC | CALL USE_ZERO | Put a zero on the calculator stack - for the 'start'. | ||
06DF | JR SA_CODE_2 | Jump forward. | ||
Look for a 'starting address'.
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SA_CODE_1 | 06E1 | CALL CLASS_06 | Fetch the first number. | |
06E4 | RST $18 | Is the present character a comma? | ||
06E5 | CP "," | |||
06E7 | JR Z,SA_CODE_3 | Jump if it is - the number was a 'starting address'. | ||
06E9 | LD A,($5C74) | However refuse 'SAVE name CODE' that does not have a 'start' and a 'length' (T-ADDR-lo=+00). | ||
06EC | AND A | |||
06ED | JP Z,REPORT_C | |||
SA_CODE_2 | 06F0 | CALL USE_ZERO | Put a zero on the calculator stack - for the 'length'. | |
06F3 | JR SA_CODE_4 | Jump forward. | ||
Fetch the 'length' as it was specified.
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SA_CODE_3 | 06F5 | RST $20 | Advance CH-ADD. | |
06F6 | CALL CLASS_06 | Fetch the 'length'. | ||
The parameters are now stored in the header area of the work space.
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SA_CODE_4 | 06F9 | CALL CHECK_END | But move on to the next statement now if checking syntax. | |
06FC | CALL FIND_INT2 | Compress the 'length' into the BC register pair and store it. | ||
06FF | LD (IX+$0B),C | |||
0702 | LD (IX+$0C),B | |||
0705 | CALL FIND_INT2 | Compress the 'starting address' into the BC register pair and store it. | ||
0708 | LD (IX+$0D),C | |||
070B | LD (IX+$0E),B | |||
070E | LD H,B | Transfer the 'pointer' to the HL register pair as usual. | ||
070F | LD L,C | |||
'SCREEN$' and 'CODE' are both of type 3.
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SA_TYPE_3 | 0710 | LD (IX+$00),$03 | Enter the 'type' number. | |
0714 | JR SA_ALL | Rejoin the other pathways. | ||
Now consider 'LINE' and 'no further parameters'.
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SA_LINE | 0716 | CP $CA | Is the present code the token 'LINE'? | |
0718 | JR Z,SA_LINE_1 | Jump if it is. | ||
071A | CALL CHECK_END | Move on to the next statement if checking syntax. | ||
071D | LD (IX+$0E),$80 | When there are no further parameters, +80 is entered. | ||
0721 | JR SA_TYPE_0 | Jump forward. | ||
Fetch the 'line number' that must follow 'LINE'.
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SA_LINE_1 | 0723 | LD A,($5C74) | However only allow 'SAVE name LINE number' (T-ADDR-lo=+00). | |
0726 | AND A | |||
0727 | JP NZ,REPORT_C | |||
072A | RST $20 | Advance CH-ADD. | ||
072B | CALL CLASS_06 | Pass the number to the calculator stack. | ||
072E | CALL CHECK_END | Move on to the next statement if checking syntax. | ||
0731 | CALL FIND_INT2 | Compress the 'line number' into the BC register pair and store it. | ||
0734 | LD (IX+$0D),C | |||
0737 | LD (IX+$0E),B | |||
'LINE' and 'no further parameters' are both of type 0.
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SA_TYPE_0 | 073A | LD (IX+$00),$00 | Enter the 'type' number. | |
The parameters that describe the program, and its variables, are found and stored in the header area of the work space.
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073E | LD HL,($5C59) | The pointer to the end of the variables area (E-LINE). | ||
0741 | LD DE,($5C53) | The pointer to the start of the BASIC program (PROG). | ||
0745 | SCF | Now perform the subtraction to find the length of the 'program + variables'; store the result. | ||
0746 | SBC HL,DE | |||
0748 | LD (IX+$0B),L | |||
074B | LD (IX+$0C),H | |||
074E | LD HL,($5C4B) | Repeat the operation but this time storing the length of the 'program' only (VARS-PROG). | ||
0751 | SBC HL,DE | |||
0753 | LD (IX+$0F),L | |||
0756 | LD (IX+$10),H | |||
0759 | EX DE,HL | Transfer the 'pointer' to the HL register pair as usual. | ||
In all cases the header information has now been prepared.
The routine continues with the first task being to separate SAVE from LOAD, VERIFY and MERGE.
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SA_ALL | 075A | LD A,($5C74) | Jump forward when handling a SAVE command (T-ADDR-lo=+00). | |
075D | AND A | |||
075E | JP Z,SA_CONTRL | |||
In the case of a LOAD, VERIFY or MERGE command the first seventeen bytes of the 'header area' in the work space hold the prepared information, as detailed above; and it is now time to fetch a 'header' from the tape.
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0761 | PUSH HL | Save the 'destination' pointer. | ||
0762 | LD BC,$0011 | Form in the IX register pair the base address of the 'second header area'. | ||
0765 | ADD IX,BC | |||
Now enter a loop, leaving it only when a 'header' has been LOADed.
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LD_LOOK_H | 0767 | PUSH IX | Make a copy of the base address. | |
0769 | LD DE,$0011 | LOAD seventeen bytes. | ||
076C | XOR A | Signal 'header'. | ||
076D | SCF | Signal 'LOAD'. | ||
076E | CALL LD_BYTES | Now look for a header. | ||
0771 | POP IX | Retrieve the base address. | ||
0773 | JR NC,LD_LOOK_H | Go round the loop until successful. | ||
The new 'header' is now displayed on the screen but the routine will only proceed if the 'new' header matches the 'old' header.
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0775 | LD A,$FE | Ensure that channel 'S' is open. | ||
0777 | CALL CHAN_OPEN | |||
077A | LD (IY+$52),$03 | Set the scroll counter (SCR-CT). | ||
077E | LD C,$80 | Signal 'names do not match'. | ||
0780 | LD A,(IX+$00) | Compare the 'new' type against the 'old' type. | ||
0783 | CP (IX-$11) | |||
0786 | JR NZ,LD_TYPE | Jump if the 'types' do not match. | ||
0788 | LD C,$F6 | But if they do, signal 'ten characters are to match'. | ||
LD_TYPE | 078A | CP $04 | Clearly the 'header' is nonsense if 'type 4 or more'. | |
078C | JR NC,LD_LOOK_H | |||
The appropriate message - 'Program: ', 'Number array: ', 'Character array: ' or 'Bytes: ' is printed.
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078E | LD DE,$09C0 | The base address of the message block. | ||
0791 | PUSH BC | Save the C register whilst the appropriate message is printed. | ||
0792 | CALL PO_MSG | |||
0795 | POP BC | |||
The 'new name' is printed and as this is done the 'old' and the 'new' names are compared.
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0796 | PUSH IX | Make the DE register pair point to the 'new name' and the HL register pair to the 'old name'. | ||
0798 | POP DE | |||
0799 | LD HL,$FFF0 | |||
079C | ADD HL,DE | |||
079D | LD B,$0A | Ten characters are to be considered. | ||
079F | LD A,(HL) | Jump forward if the match is to be against an actual name. | ||
07A0 | INC A | |||
07A1 | JR NZ,LD_NAME | |||
07A3 | LD A,C | But if the 'old name' is 'null' then signal 'ten characters already match'. | ||
07A4 | ADD A,B | |||
07A5 | LD C,A | |||
A loop is entered to print the characters of the 'new name'. The name will be accepted if the 'counter' reaches zero, at least.
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LD_NAME | 07A6 | INC DE | Consider each character of the 'new name' in turn. | |
07A7 | LD A,(DE) | |||
07A8 | CP (HL) | Match it against the appropriate character of the 'old name'. | ||
07A9 | INC HL | |||
07AA | JR NZ,LD_CH_PR | Do not count it if it does not does not match. | ||
07AC | INC C | |||
LD_CH_PR | 07AD | RST $10 | Print the 'new' character. | |
07AE | DJNZ LD_NAME | Loop for ten characters. | ||
07B0 | BIT 7,C | Accept the name only if the counter has reached zero. | ||
07B2 | JR NZ,LD_LOOK_H | |||
07B4 | LD A,$0D | Follow the 'new name' with a 'carriage return'. | ||
07B6 | RST $10 | |||
The correct header has been found and the time has come to consider the three commands LOAD, VERIFY, and MERGE separately.
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07B7 | POP HL | Fetch the pointer. | ||
07B8 | LD A,(IX+$00) | 'SCREEN$' and 'CODE' are handled with VERIFY. | ||
07BB | CP $03 | |||
07BD | JR Z,VR_CONTRL | |||
07BF | LD A,($5C74) | Jump forward if using a LOAD command (T-ADDR-lo=+01). | ||
07C2 | DEC A | |||
07C3 | JP Z,LD_CONTRL | |||
07C6 | CP $02 | Jump forward if using a MERGE command; continue into VR_CONTRL with a VERIFY command. | ||
07C8 | JP Z,ME_CONTRL |
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