Commodore 128 Programmer's Reference Manual page 309

PROGRAMMING THE 80-COLUMN (8563) CHIP 299
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UNDERSTANDING THE 80-COLUMN
CHARACTER DISPLAY AND
ATTRIBUTE MEMORY
As you learned earlier in this chapter, the 8563 has three areas of memory that control
the 80-column display: character definitions, character attributes and display screen
—| memory.
| In a previous section, the three main elements of programming the 80-column chip
were introduced: (1) the address and data registers $D600 and $D601 that map into the
C128 RAM memory map, (2) the 16K of independent 8563 RAM, and (3) the 37
internal registers. The 16K of independent 8563 RAM provide the main elements of
video display information: display memory, character attributes and character definitions.
The display memory is comparable to screen memory in the VIC chip. The character
attributes supply color and other information for the characters and parallel the function
of VIC color RAM. The 8563 character definitions correspond to the VIC character
ROM. Though the VIC and 8563 video memory are similar, the operations of the two
are different. This provides a frame of reference to the VIC chip characteristics, so you
can understand the comparison between the operation of both the VIC and 8563 video
processors.
All these video components are stored in the 16K of independent 8563 RAM.
Again, here is the breakdown of the locations where the three sections of video memory
are stored in the 8563 RAM:
TYPE OF MEMORY 8563 RAM LOCATION
Display Memory $0000-$07FF
Character Attributes $0800-$0FFF
Character Definitions $2000-$3FFF
All of the 8563 video display memory resides in the 16K section of independent
RAM. The 8563 character definitions in RAM require up to 32 bytes per character. If 32
bytes per character are used, the 8563 character definitions use 8K of memory per
character set, or a total of 16K. Otherwise, each character set occupies 4K of indepen
dent 8563 RAM, or a total of 8K for both character sets. The VIC chip requires a total
of 4K of character ROM to represent all the characters, since the VIC chip only requires
8 bytes to represent a character.
The rest of the section describes how the character display area, the character
attributes and the character definitions are addressed and interpreted.