mirror of
https://github.com/RevCurtisP/C02.git
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90 lines
3.3 KiB
NASM
90 lines
3.3 KiB
NASM
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; Program initialization code for C02 programs
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; Template for System Specific Code
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;System Specific ASCII Key Mappings
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DELKEY EQU $7F ;Delete/Backspace Key ($08=Backspace, $7F=Delete)
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ESCKEY EQU $1B ;Escape/Stop Key ($03=Ctrl-C, $1B=Escape)
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RTNKEY EQU $0D ;Return/Enter Key ($0D=Carriage Return)
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NULKEY EQU $00 ;No Key was Pressed ($00=Null)
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;Zero Page Locations
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strlo EQU $00 ;String Pointer (stdio.asm and string.asm)
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strhi EQU $01
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strlo EQU $02 ;Source String Pointer (string.asm)
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strhi EQU $04
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rdseed EQU $0E ;Pseudo-Random Seed
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random EQU $0F ;Pseudo-Random Number Storage
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temp0 EQU $10 ;Temporary Storage
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temp1 EQU $11 ;
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ORG $0200 ;Program Start Address
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start: NOP ;System specific initialization code
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TXS ;If an RTS is used to return to the Operating System,
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STX stksav ; the Stack Pointer should be preserved
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JMP main ;Execute Program
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;Read Character from Console
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getkey; ;Usually Drops into rdkey, but may need to call rdkey
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; then clean/convert returned value (e.g. Apple-1)
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;Poll Character from Keyboard
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plkey: INC rdseed ;Cycle the Random Seed (if not provided by system)
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NOP ;Code Read from Keyboad
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RTS
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;Wait for Character from Console
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rdkey: JSR plkey ;Usually calls plkey
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BEQ rdkey ; until a non-zero is returned
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RTS
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;Delete Previous Character
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delchr: RTS ;Code to move Cursor to left and clear that position
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;May work differently on systems that don't support this
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;Advance Cursor to Next line
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newlin: RTS ;Code to move Cursor to beginning of next line
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;May emit Carriage Return, Line Feed, or both
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;Print Character to Screen
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prchr: RTS ;Code to write ASCII character to Screen
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;Exit Program and Return to Operating System or Monitor
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exit: BRK ;Usually BRK if returning to Monitor
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LDX stksav ;If an RTS is used to return to the Operating System,
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TXS ; the Stack Pointer should be restored to original state
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RTS ; in case program exits in the middle of a Function
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;Note: The following two functions replicate calls available
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;in the Apple-1 monitor and are included for test purposes
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;They will likely be removed before the final release
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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 Nybb
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SED ;Set Decimal Flag for
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CLC ; Addition Wizardry
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ADC #$90 ;Convert to $90-$99,$00-$05
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ADC #$40 ;Convert to $30-$39,$41-$46
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CLD ;Clear Decimal Flag
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JMP prchr ;Print Hex Digit and Return
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;Alternate Code for Systems with Interrupts that don't CLD
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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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