mirror of
https://github.com/RevCurtisP/C02.git
synced 2024-11-28 10:51:14 +00:00
36 lines
1.2 KiB
Plaintext
36 lines
1.2 KiB
Plaintext
;Joystick Assembly Language Module for VIC-20
|
|
|
|
JYSTKS EQU $01 ;Number of Joysticks
|
|
|
|
;Joystick Bit Masks
|
|
JOYUP EQU $04 ;Bit 2 - Up
|
|
JOYDN EQU $08 ;Bit 3 - Down
|
|
JOYLF EQU $10 ;Bit 4 - Left
|
|
JOYRT EQU $01 ;Bit 1 - Right
|
|
JOYB0 EQU $20 ;Bit 5 - Button
|
|
|
|
;Read Joystick
|
|
JOYSTK: LDX #$FF ;Preset X with 255
|
|
ORA #0 ;Check Parameter
|
|
BNE JOYSTZ ;If Not Zero, Return Error
|
|
TAX ;Set X to 0
|
|
LDA $9113 ;Get DDR for Port A Status
|
|
PHA ;and Save It
|
|
LDA $9122 ;Set DDR for Port B Status
|
|
PHA ;amd Save It
|
|
STX $9113 ;Set DDR for Port A to All Inputs
|
|
STX $9122 ;Set DDR for Port B to All Inputs
|
|
LDA $9120 ;Read Port B (Right)
|
|
ASL ;Shift Bit 7 into Carry
|
|
LDA $9111 ;Read Port A
|
|
AND #$3C ;Mask Bits
|
|
ADC #0 ;Move Carry into Bit 0
|
|
EOR #$3D ;Invert Bits
|
|
TAX ;and Save in X Register
|
|
PLA ;Restore Port B DDDR
|
|
STA $9122
|
|
PLA ;Restore Port A DDDR
|
|
STA $9113
|
|
JOYSTZ: TXA ;Copy Status Back into Accumulator
|
|
RTS
|