Commodore Amiga Hardware Reference Manual page 231

Joystick Controllers
The joystick controllers have four simple direction switches and one trigger button. The
direction switches are connected to pins I, 2, 3, and 4 as FORWARD, BACK, LEFT,
and RIGHT. The trigger button is connected to pin 6.
The normal state of each of the switches is open. This places a logic 1 on each of the
input lines. When a switch is closed, it is connected to ground (pin 8), placing a logic 0
on the line.
Reading the joystick input data logic states is not so simple, however, because the data
registers for the joysticks are the same as the counters that are used for the mouse or
trackball controllers. These are named JOYODAT (port 0) and JOYIDAT (port 1).
Table 8-2 shows how to interpret the data once you have read it from these registers.
The true logic state of the switch data in these registers is "1
=
switch closed."
Table 8-2: Interpreting Data from JOYODAT and JOYIDAT
Data Bit Interpretation
1 True logic state of "right" switch.
9 True logic state of "left" switch.
1 (XOR) 0 You must calculate the exclusive-or of bits 1 and 0
to obtain the logic state of the "back" switch.
9 (XOR) 8 You must calculate the exclusive-or of bits 9 and 8
to obtain the logic state of the "forward" switch.
Proportional Controllers
Each of the game controller ports can handle two variable-resistance input devices, also
known as proportional input devices. This section describes how the positions of the
proportional input devices can be determined. There are two common types of propor-
tional controllers: the "paddle" controller pair and the X-Y proportional joystick. A
paddle controller pair consists of two individual enclosures, each containing a single
resistor and fire-button and each connected to a common controller port input connec-
tor. The typical connection is as shown in figure 8-2.
220 Interface Hardware