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23 lines
636 B
Plaintext
23 lines
636 B
Plaintext
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;Joystick Assembly Language Module for Atari 400 & 800
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JYSTKS EQU $02 ;Number of Joysticks
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;Joystick Bit Masks
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JOYUP EQU $01 ;Bit 0 - Up
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JOYDN EQU $02 ;Bit 1 - Down
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JOYLF EQU $04 ;Bit 2 - Left
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JOYRT EQU $08 ;Bit 3 - Right
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JOYB0 EQU $10 ;Bit 4 - Button
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;Read Joystick
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JOYSTK: CMP #JYSTKS ;If Invalid Joystick#
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BCS JOYSTZ ; Return Error
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EOR #$01 ;Invert Joystick Number
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TAX ;and Copy to X Register
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LDA $DC00,X ;Read Joystick
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EOR #$FF ;Invert and
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AND #$1F ;Mask Bits
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RTS
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JOYSTZ: LDA #$FF ;Return Error
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RTS
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