mirror of
https://github.com/RevCurtisP/C02.git
synced 2024-11-22 16:34:15 +00:00
90 lines
3.3 KiB
NASM
90 lines
3.3 KiB
NASM
; 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
|
|
strlo EQU $00 ;String Pointer (stdio.asm and string.asm)
|
|
strhi EQU $01
|
|
strlo EQU $02 ;Source String Pointer (string.asm)
|
|
strhi EQU $04
|
|
|
|
rdseed EQU $0E ;Pseudo-Random Seed
|
|
random EQU $0F ;Pseudo-Random Number Storage
|
|
temp0 EQU $10 ;Temporary Storage
|
|
temp1 EQU $11 ;
|
|
|
|
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
|
|
|
|
;Read Character from Console
|
|
getkey; ;Usually Drops into rdkey, but may need to call rdkey
|
|
; then clean/convert returned value (e.g. Apple-1)
|
|
|
|
;Poll Character from Keyboard
|
|
plkey: INC rdseed ;Cycle the Random Seed (if not provided by system)
|
|
NOP ;Code Read from Keyboad
|
|
RTS
|
|
|
|
;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
|
|
|