Zenith Z-100 PC series Service Manual page 279

Page
3.32
Circuit Description
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• Color/Graphics Medium Resolution Mode - In the medium resolution
graphics mode of operation, up to 200 rows of 320 pixels each may
be defined. The character and attribute data registers are linked to­
gether into one long shift register. The NCK signals shift the data
bits as 2-bit (CO and C1) pairs to the internal RGBI circuits. The CO
and C1 bit pairs are used to select 4 of 16 predetermined colors from
either of two software selected color palettes. Refer to Table 3.12.
Table 3.12. Software Selectable Color Palettes
PALETTE 1
PALETTE 2
Cyan Green
Magenta Red
Light Gray
Brown
C1
co
CODE SELECT FOR DISPLAY POSITION
0 0 Dot takes on color of 1 of 16 preselected
background colors.
0
Select 1 st color of preselected color
palette 1 or 2 (see above).
0
Select 2nd color of preselected color
palette 1 or 2 (see above).
Select 3rd color of preselected color
palette 1 or 2 (see above).
• Color/Graphics High Resolution Mode ­ In the high resolution mode,
200 rows of 640 pixels each may be defined. Due to memory limitations
however, only a monochrome display may be generated in the high
resolution mode. The character and attribute data registers are linked
together into one long shift register. The NCK signals shift each bit
(CO) of data from the character serialization register to the RGBI logic
circuits. A logic 1 gives you a pixel of foreground color determined
by the color select register 309; bits 0, 1, 2, and 3. A logic 0 blanks
the pixel.
• RGBI Logic Circuits - In the alphanumeric mode of operation, the
entire attribute data byte is used to describe the displayed character.
1