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Chapter 4 System Support
Compaq Deskpro 4000N and 4000S Personal Computers
First Edition - September 1997
4-30
Configuration Byte 26h, Auxiliary Peripheral Configuration
Default Value = 00h
Bit Function
7,6 I/O Delay Select
00 = 420 ns (default)
01 = 300 ns
10 = 2600 ns
11 = 540 ns
5 Alternative A20 Switching
0 = Disable port 92 mode
1 = Enable port 92 mode
4 Bi-directional Print Port Mode
0 = Disabled
1 = Enabled
3 Graphics Type
0 = Color
1 = Monochrome
2 Hard Drive Primary/Secondary Address Select:
0 = Primary
1 = Secondary
1 Diskette I/O Port
0 = Primary
1 = Secondary
0 Diskette I/O Port Enable
0 = Primary
1 = Secondary
Configuration Byte 27h, Speed Control/External Drive
Default Value = 00h
Bit Function
7 Boot Speed
0 = Max MHz
1 = Fast speed
6..0 Reserved
Configuration Byte 28h, Expanded and Base Memory, IRQ12 Select
Default Value = 00h
Bit Function
7 IRQ12 Select
0 = Mouse
1 = Expansion bus
6,5 Base Memory Size:
00 = 640 KB
01 = 512 KB
10 = 256 KB
11 = Invalid
4..0 Internal Compaq Memory:
00000 = None
00001 = 512 KB
00010 = 1 MB
00011 = 1.5 MB
.
.
11111 = 15.5 MB
Configuration Byte 29h, Miscellaneous Configuration Data