Three-Key Rollover (Small Keyboard)
Three-key rollover remembers the second and third keystrokes
when
three
keys are pressed before the first key
is
released. Three-key rollover
is
unpredic-
table
on
the PET
and
should not be depended upon,
as
correct
printing
depends
upon the keyboard position of ail three keys.
This section
is
only for those
readers who are interested
in
PET trivia
and
who
want
to experiment
in
three-key rollover.
The
compact
keyboard may
be
divided into odd and even rows.
as
shown in
Figure 5-1.
Figure 5-1. Odd/Even Division of
PET
Keyboard
If the three keystrokes.
KeY1. KeY2.
and
KeY3.
are not adjacent
to
each other.
then the result
is
correct and
will
be
printed
as:
(characters
of)
KeY1
KeY2 KeY3
But if the three keystrokes
are
adjacent. the resu It
is
incorrect. and the type
of error depends upon
whether
KeY1
is
in
an
odd or even column. Figure 5-2 il-
lustrates the
two
different types of errors
that
occur depending on the position of
KeY1'
To demonstrate this phenomenon. let us use three actual examples from the
keyboard.
The first example shows three non-adjacent keystrokes simultaneously
en-
tered. The diagram shows
F.
U.
N entering the buffer and then printing to the
screen
in
the correct order.
770
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