196
The
VIC
20
User
Guide
FINDING
A
CHARACTER'S
DEFINITION
IN
CHARACTER
MEMORY
•
Character definitions are stored in character memory by screen code.
The screen code is, in effect, a subscript for the character memory array.
Like screen and color memory, the character memory "array"
is
not a
BASIC variable,
but
simply a way to visualize the character memory area.
As mentioned earlier, the eight bytes
that
define a character are stored
in adjacent locations in color memory with the top row first and the bottom
row last. Here
is
how the first
few
bytes
of
Commodore's built-in character
memory, which starts
at
location 32368, are used.
Location
32768
32769
32770
32771
32772
32773
32774
32775
32776
32777
32783
32784
32785
Contents
Top row
of
"@"
Second row
of"@"
Third row of "@"
Fourth row of "@"
Fifth row of "@"
Sixth row
of
"@"
Seventh row
of"@"
Bottom row of "@"
Top row
of
"A"
Second row
of
"A"
Bottom row of
"A"
Top row
of
"B"
Second row
of"B"
This layout
of
character memory uses the following formula
to
find the
definition
of
a particular row for a given character:
Location = start
of
character memory + row + 8
...
screen code
EXPLORING
CHARACTER
MEMORY
The following program lets you choose a character and magnify it on
the screen. The program also displays other
information-such
as where the
character resides in character memory and the decimal values
of
the
rows-
that will help you become more familiar with how characters are designed.
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