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21 lines
663 B
Plaintext
21 lines
663 B
Plaintext
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;Lightpen Assembly Language Module for C64
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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 $D41A ;Check Paddle 1 (Magnum Light Phaser)
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BPL LGTPET ;If Trigger Pulled, Set X tp $FF
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LDA $DC01 ;Read Joystick Switches
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EOR #$FF ;Invert and
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AND #$1F ;Mask Bits
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BEQ LGTPEP ;If Trigger Pulled
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LGTPET: DEX ; Set X to TRUE ($FF)
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LGTPEP: LDY $D014 ;Read Y Position into Y
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LDA $D013 ;Read X Position into A
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RTS
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