READING
THE
CONTROLLER
PORT
Mouse controllers, joysticks, proportional controllers, and light pens use the same con-
nector,
but
they sometimes have considerably different functions. Therefore, the pins
function differently depending on the type of controller used.
Mouse/Trackball
Controllers
The
inputs for the mouse or trackball are the same as those for the joystick switches in
these ways:
o
The
joystick "right" and "back" switches are the same as the pins used for
mouse or trackball horizontal motion detection.
o
The
joystick "left" and "forward" switches are the same as the pins used for
mouse
or
trackball vertical motion detection.
Pulses enter these inputs from the mouse
or
trackball and are converted into an up
count
or
a down count when motion occurs. In the following discussion only
the
mouse
action
is
described;
the
trackball activity is identical.
Direction
of
Motion
versus
Count
Imagine
that
the mouse is being moved on the table over an exact image of the screen
itself.
The
movements of the on-screen object controlled. by the mouse correspond
exactly
to
the movements the user makes with the mouse itself (all directions of move-
ment are exactly the same).
The
counter counts up when the mouse
is
moved
to
the
right or "down" (toward you).
The
counter counts down when the mouse
is
moved
to
the left
or
"up"
(away from you).
The
coordinates X,Y indicate the controlled object's position on the screen.
The
coordi-
nates X=O,
y=o
are
at
the upper left-hand corner of the screen, and the coordinates
X=Xmax,
Y=Ymax
are
at
the lower right-hand corner.
Interface Hardware 217
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