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22 lines
721 B
Plaintext
22 lines
721 B
Plaintext
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;Lightpen Assembly Language Module for Atari 400 & 800
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LGTPNS EQU #$FF ;Light Pen Status (Supported)
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;Read Light Pen
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;Returns: A = X Position / 2
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; Y = Y Position
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; X = Trigger Status ($FF = Pressed)
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LGTPEN: LDX #0 ;Initialize X to FALSE (0)
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LDA $0284 ;Check Joystick Button
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EOR #$FF ;Invert and
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AND #$01 ;Mask Bits
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BEQ LGTPET ;If Trigger Pulled, Set X to $FF
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LDA $0278 ;Read Joystick Switches
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EOR #$FF ;Invert and
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AND #$0F ;Mask Bits
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BEQ LGTPEP ;If Trigger Pulled
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LGTPET: DEX ; Set X to TRUE ($FF)
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LGTPEP: LDY $0234 ;Read Y Position into Y
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LDA $0235 ;Read X Position into A
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RTS
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