Commodore Amiga A2000 - READING MOUSE;TRACKBALL CONTROLLERS

READING MOUSE/TRACKBALL CONTROLLERS
Pulses entering the mouse inputs are converted to separate horizontal and vertical counts.
The 8 bit wide horizontal and vertical counter registers can track mouse movement
without processor intervention.
The mouse uses quadrature inputs. For each direction, a mechanical wheel inside the
mouse will produce two pulse trains, one 90 degrees out of phase with the other (see
Figure 8-2 for details). The phase relationship determines direction.
The counters increment when the mouse is moved to the right or "down" (toward you).
The counters decrement when the mouse is moved to the left or "up" (away from you).
MOUSE QUADRATURE
V VQ : D1 D0
----------------
0 0 : 1 0
0 1 : 0 1
1 0 : 1 1
1 1 : 0 0
Case 1: Count up
________ ________ ________ ____
/ \ / \ / \ /
V ____/ \________/ \________/ \________/
________ ________ ________
/ \ / \ / \
VQ ________/ \________/ \________/ \__________
____ ____ ____ ____ ____ ____
/ \ / \ / 1 \ 0 / \ / \ /
D0 ____/ \____/ \____/ \____/ \____/ \____/
D1 ________ ________ ________ _________
\ / 1 \ 0 / \ /
\________/ \________/ \________/
Case 2: Count down
________ ________ ________ ____
/ \ / \ / \ /
V ____/ \________/ \________/ \________/
VQ ________ ________ ________ ________
\ / \ / \ /
\________/ \________/ \________/
D0 ____ ____ ____ ____ ____ ____
\ / \ / \ / \ / \ / \
\____/ \____/ \____/ \____/ \____/ \____
________ ________ ________
/ \ / \ / \
D1 ________/ \________/ \________/ \________
D2 ____
\
\____ etc.
Figure 8-2: Mouse Quadrature
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