;Apple 1 program initialization code for c02 programs

;System Specific ASCII Key Mappings
DELKEY  EQU $08     ;Delete/Backspace Key (Left Arrow)
ESCKEY  EQU $1B     ;Escape/Stop Key      (Escape)
RTNKEY  EQU $0D     ;Return/Enter Key     (Return)

;Standard Library Variables
DSTLO   EQU $06     ;Destination String Pointer (string.a02)
DSTHI   EQU $07
BLKLO   EQU $08     ;Block Segment Pointer (block.a02)
BLKHI   EQU $09
PTRLO   EQU $1D     ;System Pointer (pointer.a02)
PTRHI   EQU $1E
RANDOM  EQU $1F     ;Random Number
RDSEED  EQU $4E     ;O/S Random Number Low Byte 
;       EQU $4F     ;O/S Random Number High Byte
SRCLO   EQU $71     ;Source String Pointer (stdio.a02)
SRCHI   EQU $72
;           $E3     ;Unused
BLKSLO  EQU $EB     ;Block Start Address
BLKSHI  EQU $ED
BLKELO  EQU $ED     ;Block End Address
BLKEHI  EQU $EE
BLKLEN  EQU $EF     ;Block Segment Length    
TEMP0   EQU $FC     ;Temporary Storage
TEMP1   EQU $FD
TEMP2   EQU $FE
TEMP3   EQU $FF

;I/O Locations
KBD     EQU $C000   ;Keyboard Data
AKD     EQU $C010   ;Keyboard Strobe Register

;Monitor Routines
RDKEY   EQU $FD0C   ;Waits for keypress and return in A
KEYIN   EQU $FD1B   ;Waits for keypress and cycle random-number generator
RDCHAR  EQU $FD35   ;Read keyboard (processing escapes)
GETLIN  EQU $FD6A   ;Get Line from Keyboard into Input Buffer
CROUT   EQU $FD8E   ;Performs a carriage return
PRBYTE  EQU $FDDA   ;Print Accumulator as Hexadecimal Number
PRHEX   EQU $FDE3   ;Print Low Nybble of Accumulator as Hex Digit
COUT    EQU $FDED   ;Print Character in Accumulator
BELL    EQU $FF3A   ;Ring Bell through COUT
MONZ    EQU $FF69   ;Enter monitor (<Control-C>, <Return> leaves the monitor)

ECHO    EQU COUT    ;Print Character
EXIT    EQU MONZ    ;Return to Monitor

        ORG $0C00   ;Safe Area for Machine Language

START:  JMP MAIN    ;Execute Program


;Subroutine Poll Keyboard
PLKEY:  LDA #0      ;Clear Accumulator
        BIT KBD     ;Check Keyboard Strobe Bit
        BPL PLKEYR  ;If Key Pressed  
        LDA KBD     ;  Load Key Value
        STA AKD     ;  Clear Strobe
PLKEYR: RTS

;Read Keyboard
GETKEY  EQU KEYIN   ;Alias to Monitor Routine

PRCHR   EQU ECHO    ;Alias to Monitor Routine

;Delete Previous Character
DELCHR: LDX #2      ;Two Characters Total
        LDA #$88    ;Load Backspace Character
        JSR PRBLNX  ;Print Accumulator and X-1 Blanks
        LDA #$88    ;Load Backspace Character
        JMP PRCHR   ;and Print it

;Advance Character to Next line
NEWLIN   EQU CROUT  ;Alias to Monitor Routine

;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

;Retrieve Source String Pointer
GETSRC: LDX SRCLO
        LDY SRCHI
        RTS