mirror of
https://github.com/RevCurtisP/C02.git
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120 lines
3.8 KiB
NASM
120 lines
3.8 KiB
NASM
; c02 Program Initialization Code for Unexpanded VIC-20
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;ASCII Control Codes Equivalents
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CR EQU $0D ;Carriage Return
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LF EQU $11 ;Line Feed (Cursor Down)
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DEL EQU $14 ;Delete
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HT EQU $1D ;Horizontal Tab (Cursor Right)
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VT EQU $91 ;Vertical Tab (Cursor Up)
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FF EQU $93 ;Form Feed (Clear Screen)
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BS EQU $9D ;Backspace (Cursor Left)
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;PETSCII Key Mappings
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DELKEY EQU $14 ;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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strlo EQU $FB ;String Pointer (stdio.asm)
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strhi EQU $FC ;Free Byte for User Programs
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usrzp3 EQU $FD ;Free Byte for User Programs
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usrzp4 EQU $FE ;Free Byte for User Programs
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;Other RAM Locations
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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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user2 EQU $0312 ;Free Byte for User Programs
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user3 EQU $0313 ;Free Byte for User Programs
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user4 EQU $0334 ;Free Byte for User Programs
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user5 EQU $0335 ;Free Byte for User Programs
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user6 EQU $0336 ;Free Byte for User Programs
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user7 EQU $0337 ;Free Byte for User Programs
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user8 EQU $0338 ;Free Byte for User Programs
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user9 EQU $0339 ;Free Byte for User Programs
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user10 EQU $033A ;Free Byte for User Programs
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user11 EQU $033B ;Free Byte for User Programs
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tbffr EQU $033C ;Cassette I/O Buffer
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user12 EQU $03FC ;Free Byte for User Programs
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user13 EQU $03FD ;Free Byte for User Programs
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user14 EQU $03FE ;Free Byte for User Programs
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user15 EQU $03FF ;Free Byte for User Programs
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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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;Kernal Routines
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chrin EQU $FFCF ;Input Character to Channel
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chrout EQU $FFD2 ;Output Character to Channel
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getin EQU $FFE4 ;Read Character from Keyboard Buffer
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;Machine Language Basic Stub
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ORG $1001 ;Start
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basic: DC $0C, $10 ; Pointer to Next Line (4108)
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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 $34, $31, $31 ,$30 ; "4110"
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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 user15 ;and Save for Exit
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JMP main ;Execute Program
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exit: LDX user15 ;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 getin ;Read Character from Keyboard Buffer
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;Get Character from Keyboard
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getkey:
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;Wait for Character from Keyboard
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rdkey: JSR plkey ;Poll Keyboard
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BEQ getkey ;If No Key, Loop
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RTS
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;Delete Previous Character
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delchr: RTS
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;Advance Character to Next line
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newlin: LDA #$0D ;Load C/R into Accumulator
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;Print Character to Console
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prchr EQU chrout ;
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;Delete Previous Character
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delchr: LDA #$9D ;Load Cursor Left into Accumulator
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JSR prchr ; and Print it
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LDA #$14 ;Load Delete into Accumulater
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JMP prchr ; and Print it
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;Advance Character to Next line
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newlin: LDA #$0D ;Load C/R into Accumulator
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JMP prchr ; and Print it
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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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exit: RTS ;Return to Monitor
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