Commodore 128 Programmer's Reference Manual page 235

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THE POWER BEHIND COMMODORE 128 GRAPHICS 225
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different due to the way they are stored in the character ROM. Notice in Appendix D
that the screen code for an at-sign (@) is 0. The @ is numbered 0 because it is the first
character to be stored in the character ROM. The letter "A" is the second character
ROM; therefore its code is 1. The letter "B" is the third character in the character
ROM, etc. The screen code is actually an index from the starting location of the
character ROM, beginning with zero.
If you want to POKE a character directly into screen memory, use the screen code
rather than the ASCII character string (CHR$) code. The same holds true for the
machine language monitor. For example:
POKE 1024,1
places the letter A in the HOME position on the VIC screen. From the monitor, placing
the value 1 in location $0400 (decimal 1024) also displays the letter A in the HOME
position on the VIC screen.
COLOR DATA
In standard character mode, color information comes from color RAM, in the address
range 55296 ($D800) through 56295 ($DBE7). This memory determines the color of the
characters in each of the 1,000 screen locations. The background color of the screen is
determined by the background color register 0 which is location 53281.
The color RAM and the screen RAM locations correspond on a one-to-one basis.
Screen location 1024 pertains to color RAM location 55296; screen location 1025
corresponds to color location 55297, etc. Figure 8-13 is the color RAM memory map.
The map shows how color RAM corresponds to the locations in screen RAM and the
placement on your video display.
COLOR MEMORY MAP
COLUMN
10 20
30
55335
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1 1
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55296
55336
55376
55416
55456
55496
55536
55576
55616
55656
55696
55736
55776
55816
55856
55896
55936
55976
56016
56056
56096
56136
56176
56216
56256
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Figure 8-13. Color Memory Map
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56295