ALTERNATE CHARACTER SET
Another
PET
feature
is
its dual character
set.
made up of a "standard" and
an
"alternate" character set.
For
most keyboards the Standard Charaeter
Set
eonsists of capital,
or
upper-case alphabetic characters,
and
graphie charac-
ters. The Alternate Character
Set
is
upper case alphabetic characters,
shifted lower-case alphabetics
and
about half of the graphie eharacters.
On
the CBM, standard and alternate character sets are reversed. The difference
between the
two
character sets occurs
in
shifted mode:
Standard Character
Set
Alternate Character
Set
Unshifted Upper-case alphabeties Upper-case alphabeties
mode
Shifted
Graphies
Lower-ease alphabeties
mode some graphies
The Alternate Character Set
is
put into effect by POKEing a special value
into a specified location
in
memory. The contents of memory address
59468
determines which character set
is
in
operation. When memory location 59468
contains the value 12 or 13, the Standard Character Set
is
in
use.
If
location 59468
contains any value from 0 to
11,
or 14 to 255, the Alternate Character Set
is
in
effect:
Contents of Memory Location 59468
0.1.2.3.4.5.6.7.8.9.10.11
12.13
14.15
...
255
Charaeter Set in Operation
alternate
standard
alternate
For the purpose of simplicity, we
will
always
use
value
12
to designate the
Standard Character Set and value 14 for the Alternate Character
Set.
Figure 5-10
is
a flowchart of the Standard/Alternate Character Set decision.
273
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