Commodore Amiga A2000 - GAME PORT INTERFACE TO DIGITAL JOYSTICKS

GAME PORT INTERFACE TO DIGITAL JOYSTICKS
A joystick is a device with four normally opened switches arranged 90
degree apart. The JOY[0/1]DAT registers become encoded switch input
port as follows:
Forward: bit9 xor bit#8
Left: bit9
Back: bit1 xor bit0
Right: bit1
Data is encoded to facilitate the mouse/trackball operating mode.
NOTE: The right and left direction inputs are also designed to be
right and left buttons, respectively, for use with proportional
input. In this case, the forward and back inputs are not used,
while right and left become button inputs rather than joystick inputs.
The JOY[0/1]DAT registers are always valid and may be read at any time.
CONNECTOR PIN USAGE FOR DIGITAL JOYSTICK INPUTS
PIN MNEMONIC DESCRIPTION HARDWARE REGISTER/NOTES
--- -------- ----------- -----------------------
1 FORWARD* Forward joystick switch JOY[0/1]DAT<9 xor 8>
2 BACK* Back joystick switch JOY[0/1]DAT(1 xor 0>
3 LEFT* Left joystick switch JOY[0/1]DAT<9>
4 RIGHT* Right joystick switch JOY[0/1]DAT<1>
5 Unused
6 FIRE* Left mouse button See Fire Button.
7 +5V 125ma max, 200ma surge Total both ports.
8 Ground
9 Unused
GAME PORT INTERFACE TO FIRE BUTTONS
The fire button are normally opened switches routed to the 8520
adapter PRA0 a follow:
PRA0 bit 7 - Fire* left controller port
PRA0 bit 6 - Fire* right controller port
Before reading this register, the corresponding bits of the data
direction register must be cleared to define input mode:
DDRA0<7:6> cleared as appropriate
NOTE: Do not disturb the settings of other bits in DDRA0 (Use of ROM
kernel call is recommended).
Fire buttons are always valid and may be read at any time.
- Appendix E 307 -