Commodore 1351 Benutzerhandbuch Seite 36

3)
The
right
mouse
button
is
mapped
to
what would be
the
UP
direction
on a
joystick
Software
Interface:
1
Because
the
left
and
right
buttons
appear as
joystick
lines,
reading
them
from software
is
a
simple exercise
in
polling.
Note
that
as
with
a
joystick,
the buttons
will
interfere
with the
keyboard map, and
software should
make some
effort to
distinguish
between a
point short
in
the
keyboard
matrix
(i.e.,
a key
being depressed),
and
a whole row
or
column
being
grounded
(i.e.,
a
joystick
type
of signal).
2)
The
position
information
is
not
difficult
to
handle.
Ideally
is
should
be
installed
as
part
of
the
60
Hz
interrupt routine (pre-
ferably at
the beginning
—
see
the section
on SID REGI-
STER
CAUTIONS).
This
strategy
is
as
follows:
1
Read
the
mouse
position
MOD
64.
2)
Determine
if
the
mouse
has
moved
by comparing
the
current position with
a saved copy
of
the previous
position.
3)
If
the
mouse
has moved,
then modify your
pointer position
appropriately.
You
should
note, that
even
if
the
mouse
is
still,
it
is
possible
for
the
POT
register
to oscillate
between
$80
and
$7F.
This
would
result
in
the
mouse
position
as
jittering
bet-
ween
two
points.
In
order
to
asertain
wether
the
mouse
has
moved
the software
should read the low order
bit
of
the
POT
register.
All
of
this
can be seen
in
the supplied
mouse
driver
code.
32
English