Compaq 850 manual Configuration Byte 27h, Speed Control/External Drive

Technical Reference Guide

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

5Alternative A20 Switching 0 = Disable port 92 mode 1 = Enable port 92 mode

4Bi-directional Print Port Mode 0 = Disabled

1 = Enabled

3Graphics Type 0 = Color

1 = Monochrome

2Hard Drive Primary/Secondary Address Select: 0 = Primary

1 = Secondary

1Diskette I/O Port 0 = Primary

1 = Secondary

0Diskette 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

7IRQ12 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

Compaq Deskpro EXS and Workstation 300 Personal Computers 4-27

Featuring the Intel Pentium 4 Processor

First Edition - December 2000