;Lightpen Assembly Language Module for Atari 400 & 800

LGTPNS  EQU #$FF        ;Light Pen Status (Supported)

;Read Light Pen
;Returns: A = X Position / 2
;         Y = Y Position
;         X = Trigger Status ($FF = Pressed)
LGTPEN: LDX #0      ;Initialize X to FALSE (0)
        LDA $0284   ;Check Joystick Button
        EOR #$FF    ;Invert and
        AND #$01    ;Mask Bits
        BEQ LGTPET  ;If Trigger Pulled, Set X to $FF
        LDA $0278   ;Read Joystick Switches
        EOR #$FF    ;Invert and
        AND #$0F    ;Mask Bits
        BEQ LGTPEP  ;If Trigger Pulled
LGTPET: DEX         ;  Set X to TRUE ($FF)
LGTPEP: LDY $0234   ;Read Y Position into Y
        LDA $0235   ;Read X Position into A
        RTS