Table 8-2: Determining the Direction of the Mouse
Previous Current Direction
Count Count
200 100 Up (Left)
100 200 Down (Right)
200 45 Down *
45 200 Up **
NOTES FOR Table 8-1:
* Because 200-45 = 155, which is more than 127, the true count must be 255 - ( 200-45)
= 100; the direction is down.
** 45-200 = -155. Because the absolute value of -155 exceeds 127, the true count must
be 255 + (-155) = 100; the direction is up.
MOUSE BUTTONS
There are two buttons on the standard Amiga mouse. However, the control circuitry and
software support up to three buttons.
o The left button on the Amiga mouse is connected to, CIAAPRA ($BFE001). The button
for port 1 is connected to bit 6, port 2 is connected to bit 7. See the 8520 Appendix for
more information. A logic state of 1 means "switch open." A logic state of 0 means "switch
closed."
o Button 2 (right button on Amiga mouse) is connected to pin 9 of the controller ports,
one of the proportional pins. See "DIGITAL INPUT/OUTPUT ON THE CONTROLLER PORT"
for details.
o Button 3, when used, is connected to pin 5, the other proportional controller input.
READING DIGITAL JOYSTICK CONTROLLERS
Digital joysticks contain four directional switches. Each switch can be individually activated
by the control stick. When the stick is pressed diagonally, two adjacent switches are
activated. The total number of possible directions from a digital joystick is 8. All digital
joysticks have at least one fire button.
- 226 Interface Hardware -
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