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100 lines
3.5 KiB
Plaintext
100 lines
3.5 KiB
Plaintext
;c02 Program Initialization Code for VIC-20 with 3K Expansion
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;System Specific ASCII Key Mappings
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DELKEY EQU $7F ;Delete/Backspace Key (Delete)
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ESCKEY EQU $03 ;Escape/Stop Key (RUN/STOP)
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RTNKEY EQU $0D ;Return/Enter Key (RETURN)
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;Zero Page Locations
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SRCLO EQU $22 ;Source Pointer LSB [Temporary Pointers]
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SRCHI EQU $23 ;Source Pointer MSB [Temporary Pointers]
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DSTLO EQU $25 ;Destination Pointer LSB [Temporary Pointers]
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DSTHI EQU $24 ;Destination Pointer MSB [Temporary Pointers]
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RDSEED EQU $A2 ;Random Seed [Software Jiffy Clock (Low Byte)]
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BLKLO EQU $FD ;Block Pointer LSB [Unused Byte]
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BLKHI EQU $FE ;Block Pointer MSB [Unused Byte]
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STKLO EQU $FD ;Stack Pointer LSB [Unused Byte]
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STKHI EQU $FE ;Stack Pointer MSB [Unused Byte]
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USER0 EQU $0310 ;Free Byte for User Programs
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USER1 EQU $0311 ;Free Byte for User Programs
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STKSAV EQU $0312 ;Machine Stack Storage [Unused Byte]
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STKSLO EQU $0313 ;Stack Start LSB [Unused Byte]
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STKSHI EQU $0334 ;Stack Start MSB [Unused Byte]
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STKELO EQU $0335 ;Stack End LSB [Unused Byte]
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STKEHI EQU $0336 ;Stack End MSB [Unused Byte]
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BLKSLO EQU $0337 ;Block Start LSB [Unused Byte]
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BLKSHI EQU $0338 ;Block Start MSB [Unused Byte]
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BLKELO EQU $0339 ;Block Start MSB [Unused Byte]
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BLKEHI EQU $033A ;Block End MSB [Unused Byte]
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BLKLEN EQU $033B ;Block Length [Unused Byte]
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TBFFR EQU $033C ;Cassette I/O Buffer
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TEMP0 EQU $03FC ;Temporary Variable [Unused Byte]
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TEMP1 EQU $03FD ;Temporary Variable [Unused Byte]
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TEMP2 EQU $03FE ;Temporary Variable [Unused Byte]
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TEMP3 EQU $03FF ;Temporary Variable [Unused Byte]
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;Video RAM and ROM
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VICSCN EQU $1E00 ;Video Screen Memory Area (Unexpanded)
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CHRROM EQU $8000 ;Character Generator ROM
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VICCLR EQU $9600 ;Color RAM (Unexpanded)
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;Machine Language Basic Stub
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ORG $0401 ;Start
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BASIC: DC $0C, $04 ; Pointer to Next Line (1036)
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DC $00, $00 ; Line Number (0)
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DC $9E ; SYS
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DC $20 ; ' '
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DC $31, $30, $33 ,$38 ; "1038"
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DC $00 ;End of Line Marker
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DC $00, $00 ;End of Basic Program
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START: TSX ;Get Stack Pointer
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STX STKSAV ;and Save for Exit
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JMP main ;Execute Program
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EXIT: LDX STKSAV ;Retrieve Saved Stack Pointer
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TXS ;and Restore It
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RTS ;Return to BASIC
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;Poll Keyboard for Character
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PLKEY EQU $FFE4 ;Aliased to Kernal GETIN Routine
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;Get Character from Keyboard
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GETKEY EQU PLKEY
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;Wait for Character from Keyboard
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RDKEY: JSR GETKEY ;Poll Keyboard
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BEQ RDKEY ;If No Key, Loop
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RTS
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;Delete Previous Character
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DELCHR: LDA #DELKEY ;Load Delete Character
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JMP PRCHR ;Print and Return
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;Advance Character to Next line
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NEWLIN: LDA #RTNKEY ;Load C/R into Accumulator
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JMP PRCHR ;Print and Return
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;Print Character to Console
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PRCHR EQU $FFD2 ;Aliased to Kernal CHROUT Routine
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;Print Byte as Two-Digit Hex Number to Console
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PRBYTE: PHA ;Save Accumulater
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LSR ;Shift Hi Nybble to Low Nybble
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LSR
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LSR
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LSR
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JSR PRHEX ; and Print it
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PLA ;Restore Accumulator
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; and fall into prhex
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;Print Low Nybble as Hex Digit to Console
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PRHEX: AND #$0F ;Strip High Nybble
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CMP #$0A ;If Low Nybble >= 10
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BCC PRHEXC ;
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ADC #$06 ; Convert ':' to 'A'...
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PRHEXC: ADC #$30 ;Convert to ASCII Character
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JMP PRCHR ;Print Hex Digit and Return
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