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C02/include/header.a02
2018-01-28 13:30:49 -05:00

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; Program initialization code for C02 programs
; Template for System Specific Code
;System Specific ASCII Key Mappings
DELKEY EQU $7F ;Delete/Backspace Key ($08=Backspace, $7F=Delete)
ESCKEY EQU $1B ;Escape/Stop Key ($03=Ctrl-C, $1B=Escape)
RTNKEY EQU $0D ;Return/Enter Key ($0D=Carriage Return)
NULKEY EQU $00 ;No Key was Pressed ($00=Null)
;Zero Page Locations
SRCLO EQU $00 ;Source String Pointer (stdio.asm)
SRCHI EQU $01
DSTLO EQU $02 ;Destination String Pointer (string.asm)
DSTHI EQU $03
STKSAV EQU $0D ;Stack Pointer Storage
RDSEED EQU $0E ;Pseudo-RANDOM Seed
RANDOM EQU $0F ;Pseudo-RANDOM Number Storage
TEMP0 EQU $10 ;Temporary Storage
TEMP1 EQU $11
TEMP2 EQU $12
BLKSLO EQU $20 ;Block Start Address
BLKSHI EQU $21
BLKELO EQU $22 ;Block End Address
BLKEHI EQU $23
ORG $0200 ;Program Start Address
START: NOP ;System specific initialization code
TXS ;If an RTS is used to return to the Operating System,
STX STKSAV ; the Stack Pointer should be preserved
JMP MAIN ;Execute Program
;Poll Character from Keyboard
PLKEY: INC RDSEED ;Cycle the Random Seed (if not provided by system)
NOP ;Code Read from Keyboad
RTS
;Read Character from Console
GETKEY; ;Usually Drops into RDKEY, but may need to call RDKEY
; then clean/convert returned value (e.g. Apple-1)
;Wait for Character from Console
RDKEY: JSR PLKEY ;Usually calls PLKEY
BEQ RDKEY ; until a non-zero is returned
RTS
;Delete Previous Character
DELCHR: RTS ;Code to move Cursor to left and clear that position
;May work differently on systems that don't support this
;Advance Cursor to Next line
NEWLIN: RTS ;Code to move Cursor to beginning of next line
;May emit Carriage Return, Line Feed, or both
;Print Character to Screen
PRCHR: RTS ;Code to write ASCII character to Screen
;Exit Program and Return to Operating System or Monitor
EXIT: BRK ;Usually BRK if returning to Monitor
LDX STKSAV ;If an RTS is used to return to the Operating System,
TXS ; the Stack Pointer should be restored to original state
RTS ; in case program exits in the middle of a Function
;Note: The following two functions replicate calls available
;in the Apple-1 monitor and are included for test purposes
;They will likely be removed before the final release
;Print Byte as Two-Digit Hex Number to Console
PRBYTE: PHA ;Save Accumulater
LSR ;Shift Hi Nybble to Low Nybble
LSR
LSR
LSR
JSR PRHEX ; and Print it
PLA ;Restore Accumulator
; and fall into PRHEX
;Print Low Nybble as Hex Digit to Console
PRHEX: AND #$0F ;Strip High Nybb
SED ;Set Decimal Flag for
CLC ; Addition Wizardry
ADC #$90 ;Convert to $90-$99,$00-$05
ADC #$40 ;Convert to $30-$39,$41-$46
CLD ;Clear Decimal Flag
JMP PRCHR ;Print Hex Digit and Return
;Alternate Code for Systems with Interrupts that don't CLD
PRHEX: AND #$0F ;Strip High Nybble
CMP #$0A ;If Low Nybble >= 10
BCC PRHEXC ;
ADC #$06 ; Convert ':' to 'A'...
PRHEXC: ADC #$30 ;Convert to ASCII Character
JMP PRCHR ;Print Hex Digit and Return
;Functions to set String Pointers
;Used by memory, stdio, stdlin, string, and stringx libraries
;Initialize Destination String Pointer and Index
SETDST: STX DSTLO ;Save Destination String Pointer
STY DSTHI
RTS
;Initialize Source String Pointer and Index
SETSRC: STX SRCLO ;Save Source String Pointer
STY SRCHI
LDY #$00 ;Initialize Index Into String
RTS