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34 lines
1.1 KiB
Plaintext
34 lines
1.1 KiB
Plaintext
;Paddle Controller Constants and Functions for Atari 400 & 800
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PADDLS EQU #$08 ;Maximum Numbers of Paddles
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;Read Paddle
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;Args: A = Paddle #
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;Affects: X
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;Returns: A = Paddle Value
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; 0 and Carry Set if Paddle # Invalid
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PADDLE: CMP #PADDLS ;If Invalid Paddle #
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BCS BUTTOZ ; Return 0 & Carry Set
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TAX ;Copy Paddle # to X
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LDA $0270,X ;Read Paddle Shadow Register
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RTS
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BUTTNS EQU #$04 ;Maximum Numbers of Paddle Buttons
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;Read Paddle Button
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;Args: A = Button #
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;Affects: X,Y
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;Returns: A = $FF if Paddle Button Pressed
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; $00 if Paddle Button Not Pressed
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; Carry Set if Button Number Invalid
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BUTTON: CMP #BUTTNS ;If Button# >= # of Buttons
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BCS BUTTOZ ; Return FALSE & Carry Set
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TAX ;and Copy to X Register
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LDA $027C,Y ;Read Button Shadow Register
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AND #$01 ;Mask off Relevant Bit
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BNE BUTTOZ ;If Bit is 0
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LDA #$FF ; Return TRUE
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RTS ;Else
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BUTTOZ: LDA #$00 ; Return FALSE
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RTS
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