;Apple 1 program initialization code for c02 programs

        SUBROUTINE  _APPLE2

;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)

;Zero Page Variables (*=System Variable)
DSTLO   EQU $06     ;Destination Pointer
DSTHI   EQU $07
BLKLO   EQU $08     ;Block Segment Pointer (block.a02)
BLKHI   EQU $09
STKLO   EQU $1D     ;Stack Pointer (stack.a02)
STKHI   EQU $1E
RANDOM  EQU $1F     ;Random Number
INVFLG  EQU $32     ;*Inverse Flag: $3F=Blinking, $7F=Inverse, $FF=Normal 
SRCLO   EQU $71     ;Source Pointer
SRCHI   EQU $72
RDSEED  EQU $E3     ;Random Seed
BLKSLO  EQU $EB     ;Block Start Address
BLKSHI  EQU $ED
BLKELO  EQU $ED     ;Block End Address
BLKEHI  EQU $EE
BLKLEN  EQU $EF     ;Block Segment Length    
BFRLO   EQU $FA     ;Work Buffer Pointer
BFRHI   EQU $FB
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
PRBYTE  EQU $FDDA   ;Print Accumulator as Hexadecimal Number
PRHEX   EQU $FDE3   ;Print Low Nybble of Accumulator as Hex Digit
EXIT    EQU $03D0   ;Return to Monitor - Jump Vector to DOS warm start

        ORG $0C00   ;Safe Area for Machine Language

START:  JSR NEWLIN  ;Start On New Line
        JMP MAIN    ;Execute Program

;Poll Keyboard for Raw Character
POLKEY: INC RDSEED  ;Cycle Random Seed
        LDA #0      ;Clear Accumulator
        BIT .KBD     ;Check Keyboard Strobe Bit
        BPL POLKER  ;If Key Pressed  
        LDA .KBD     ;  Load Key Value
        STA .AKD     ;  Clear Strobe
POLKER: RTS

;Get ASCII Character from Keyboard
GETKEY: JSR POLKEY  ;Poll Keyboard
        AND #$7F    ;Strip High Bit
        RTS

;Wait for ASCII Character from Keyboard
GETCHR: JSR GETKEY  ;Get Modified Key Code
        BEQ GETCHR  ;Loop if No Key	
        RTS

;Delete Previous Character
DELCHR: LDX #2      ;Two Characters Total
        LDA #$88    ;Load Backspace Character
        JSR $F94C   ;Monitor Routine PRBLAX
        LDA #DELKEY ;Load Backspace Character
                    ;and Fall into PRCHR

;Print Character to Screen
PUTCHR: ORA #$80    ;Set High Bit
        CMP #$E0    ;
        BCC PRCHRX  ;If Lower Case 
        AND #$1F    ;  Convert to Inverse
PRCHRX: JMP $FDF0   ;Execute Monitor Routine COUT1

;Advance Character to Next line
NEWLIN   EQU $FD8E  ;Monitor Routine CROUT

        INCLUDE "../include/putstr.a02" ;PUTSTR routine