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58 lines
2.0 KiB
Plaintext
58 lines
2.0 KiB
Plaintext
;Paddle Controller Constants and Functions for C64
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PADDLS EQU #$04 ;Maximum Numbers of Paddles
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;Read Paddle
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;Args: A = Paddle #
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;Affects: X,Y
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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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EOR #$03 ;Invert Paddle #
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TAY ;Copy Paddle # to Y
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AND #$01 ;Get Paddle Index
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TAX ;and Copy to X
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SEI ;Turn off Interrupts
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LDA $DC02 ;Save Data Direction Register A
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PHA
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LDA #$C0
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STA $DC02 ;Set Port A for Output
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LDA PADDLT,Y ;Get Bit Mask and
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STA $DC00 ;Address Pair of Paddles
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LDY #$FF ;Wait for SID to Read Paddles
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PADDLL: NOP
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DEY
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BMI PADDLL ;Y contains $7F when Done
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PLA ;Restore Data Direction Register A
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STA $DC02
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LDA $D419,X ;Read Paddle
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STY $DC00 ;Reset Port A for Button Read
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CLI ;Turn on Interrupts
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RTS
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PADDLT: DC $80,$80,$40,$40 ;Port A Bit Mask Table
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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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EOR #$03 ;Invert Button #
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TAX ;and Copy to X Register
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ROR ;Divide Button # by 2
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TAY ;and Transfer to Y Register
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LDA $DC00,Y ;Read Joystick Port
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AND BUTTOM,X ;Mask off Relevant Bit
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BNE BUTTOZ ;If Bit is 0
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LDA #$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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;Paddle Buttons 0 = S2 (bit 2), 1 = S3 (bit 3)
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BUTTOM: DC $08,$04,$08,$04 ;Paddle Button Bit Masks
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