Zenith Z-100 PC series Service Manual page 266

Page
3.19
Circuit Description
• Mode Select Registers - The mode select registers are also write-only
registers. One is a 6-bit register at port address 30B; the other is
an B-bit register at 30A. Both can be written to using 1/0 OUT com ­
mands. The output register at 30B functions according to the logic
of Table 3.B.
Table 3.B. Mode Select Port 308 Logic
MODE
o
BITS
2
3
4 5
40 x 25ALPHAB& W
40
x
25 ALPHA COLOR
80 x 25ALPHAB& W
80 x 25 ALPHA COLOR
320
x
200 B & W GRAPHICS
320 x 200 COLOR GRAPHICS
640 x 200 B & W GRAPHICS
o
o
1
1
o
o
o
o
o
o
o
1
1
0
1
0
1
0
1
o
o
o
o
o
o
1
1
1
X
X
X
Bits
0-80 x 25 ALPHA SELECT
1 - SELECT 320
x
200 GRAPHICS
2 ­ SELECT B & W MODE
3- ENABLE VIDEO
4-640
x
200B&W
5- ENABLE BLINK ATTRIBUTE
x -
Does Not Care