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49 lines
1.7 KiB
Plaintext
49 lines
1.7 KiB
Plaintext
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;Paddle Controller Constants and Functions for VIC-20
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PADDLS EQU #2 ;Maximum Numbers of Paddles
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;Read Paddle
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;Args: A = Paddle #
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;Returns: A,Y = Paddle Value
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; 0 and Carry Set if Paddle # Invalid
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; X = Paddle #
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PADDLE: LDY #0 ;Preset Result to 0
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CMP #PADDLS ;If Paddle# >= # of Paddles
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BCS PADDLZ ; Return Zero & Carry Set
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TAX ;Copy Paddle # to X Register
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LDY $9008,X ;Read Paddle
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PADDLZ: TYA ;Copy Result to Accumulator
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RTS
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BUTTNS EQU #2 ;Maximum Numbers of Paddle Buttons
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;Read Paddle Button
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;Args: A = Button #
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;Affects: 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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; X = Button #
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BUTTON: CMP #2 ;If Button# >= # of Buttons
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BCS BUTTOZ ; Return FALSE & Carry Set
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TAX ;Copy Button Number to X Register
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LDY BUTTOR,X ;Get Button Register Offset
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LDA $9102,Y ;Read Data Direction Register
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PHA ;and Save It
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LDA #$00 ;Set Port to All Inputs
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STA $9102,Y ;
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LDA $9100,Y ;Read Button Port
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AND BUTTOM,X ;and Isolate Bit
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TAX ;Save Result in X
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PLA ;Retrieve Original DDR Value
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STA $9102,Y ;Restore Data Direction Register
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TXA ;Get Result from X, Setting Flags
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BNE BUTTOZ ;If Bit Not Set
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LDA #$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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;Paddle Buttons 0 = S2 ($9111 bit 4), 1 = S3 ($9120 bit 7)
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BUTTOR: DC $11,$20 ;Paddle Button VIC Registers
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BUTTOM: DC $10,$80 ;Paddle Button Bit Masks
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