;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)
DSTPTR  EQU $06     ;Destination Pointer [Unused]
BLKPTR  EQU $08     ;Block Segment Pointer [Unused]
SYSBFP  EQU $1D     ;Stack Pointer [Unused]
;           $1E     ;Unused
STKLO   EQU $2E     ;Stack Pointer [Tape Read Work Area]
STKHI   EQU $2F
RANDOM  EQU $1F     ;Random Number
.INVFLG EQU $32     ;*Inverse Flag: $3F=Blinking, $7F=Inverse, $FF=Normal 
SRCPTR  EQU $71     ;Source Pointer [Temporary Register]
RDSEED  EQU $E3     ;Random Seed
BLKBGN  EQU $EB     ;Block Start Address [Unused]
BLKEND  EQU $ED     ;Block End Address [Unused]
BLKLEN  EQU $EF     ;Block Segment Length [Unused]
BFRLO   EQU $FA     ;Work Buffer Pointer [Unused]
BFRHI   EQU $FB
TEMP0   EQU $FC     ;Temporary Variables [Unused]
TEMP1   EQU $FD
TEMP2   EQU $FE
TEMP3   EQU $FF

;System Variables
SYSBFL  EQU 255    ;System Buffer Size [88 Bytes]
SYSBFR  EQU $0300 ;System Buffer [Keyboard Buffer]


;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