C02/include/x16/joystk.a02

;Joystick Constants and Functions
;for Commander X16 Computer

JYSTKS  EQU 2       ;Number of Joysticks

.JYDATA  EQU $02BC   ;Joystick 0 Data

.GETJOY  EQU $FF06   ;Kernal GETJOY Routine

;Joystick Bit Masks
JOYUP   EQU $08     ;Up    
JOYDN   EQU $04     ;Down  
JOYLF   EQU $02     ;Left  
JOYRT   EQU $01     ;Right 
JOYB0   EQU $80     ;Button

;Read Joystick
JOYSTK: CMP #JYSTKS     ;If Invalid Joystick Number
        BCS JOYSTE      ;  Return ERROR
        STA TEMP0       ;Save Joystick Number
        JSR $FF06       ;Call Kernal GETJOY Routine
        LDA TEMP0       ;Retrieve Joystick Number
        ASL             ;Multiply it by 3
        ADC TEMP0       ;(Assumes Number<128)
        TAX             ;and Copy to X-Register
        LDA $02BE,X     ;If Controller Not Present
        BNE JOYSTE      ;  Return ERROR
        LDA $02BC,X     ;Read Controller Status
        ;EOR #$FF        ;Invert Bits
        AND #$CF        ;and Mask off Select/Start
        RTS
JOYSTE: LDA #255        ;Return Error Code
        RTS