Commodore Amiga - Page 284

00
GAME PORT INTERFACE TO DIGITAL JOYSTICKS
A joystick is a device with four normally opened switches arranged 90
degrees apart. The JOY[O/l]DAT registers become encoded switch input
ports as follows:
Forward:
Left:
Back:
Right:
bit#9 xor bit#8
bit#9
bit#l xor bit#O
bit#l
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
inputs. In this case, the forward and back inputs are not used,
while right and left become button inputs rather than joystick inputs.
The JOY[O/l]DAT registers are always valid and may be read at any time.
CONNECTOR PIN USAGE FOR DIGITAL JOYSTICK INPUTS
PIN
MNEMONIC
DESCRIPTION
1
FORWARD' Forward joystick switch
2
BACK'
Back joystick switch
3
LEFT' Left joystick switch
4
RIGHT'
Right joystick switch
5 Unused
6
FIRE' Left mouse button
7
+5V
12Sma max, 200ma surge
8
Ground
9
Unused
GAME PORT INTERFACE TO FIRE BUTTONS
HARDWARE REGISTERjNOTES
JOY[0/1]DAT<9 xor 8>
JOY[O/l]DAT(l
xor 0>
JOY [0/1] DAT<9>
JOY [0/1] DAT<l>
See Fire Button ..
Total both ports.
The fire buttons are normally opened switches routed to the 8520
adapter PBAO as follows:
PRAO bit 7 = Fire' left controller port
PBAO 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:
DDBAO<7:6> cleared as appropriate
NOTE: Do not disturb the settings of other bits in DDBAO (Use of ROM
kernel calls is recommended).
Fire buttons are always valid and may be read at any time.
CONNECTOR PIN USAGE FOR FIRE BUTl'ON INPUTS
PIN
MNEMONIC
DESCRIPTION
1
-x-
2
-x-
3
-x-
4
-x-
5
-x-
6
FIRE'
Left mouse button/fire button
7
-x-
8
-x-
9
-x-
GAME PORT INTERFACE TO PROPORTIONAL CONTROLLERS
Resistive ~tentiometer) element linear taper proportional
controllers are supported up to 528k Ohms max (470k +/- 10%
recommended). The JOY[O/l]DAT registers contain digital
translation values for y in the high byte and x in the low byte.
A higher count value indicates a higher external resistance.
The Amiga performs an integrating analog-to-digital conversion
as follows:
1. POT[O/l]DAT registers are reset and the analog input capacitors
are discharged for the first 7 (261 lines) or 8 (262 lines)
horizontal lines.
2. Once per horizontal line, each analog input is conpared to an
internal reference.
3. Any counter whose analog input exceeds the reference stops
incrementing. The counter is stopped for the duration of the
vertical frame.
4. Any counter whose analog input is less than the reference
continues to increment.
NOTE: The POTY and POTX inputs are designated as "right mouse button"
and "unused mouse button" respectively. An opened switch
corresponds to high resistance, a closed switch to a low
resistance. The buttons are also available in POTGO and
POTINP registers. It is recommended that ROM kernel calls
be used for future hardware conpatibility.
The POT[O/l]DAT registers are typically read during video blanking,
but MAY be available prior to that.