Chapter 4 System Support
Configuration Bytes 19h-1Ch, Hard Drive Types
Byte 19h contains the hard drive type for drive 1 of the primary controller if byte 12h bits <7..4>
hold 1111b. Byte 1Ah contains the hard drive type for drive 2 of the primary controller if byte 12h
bits <3..0> hold 1111b. Bytes1Bh and 1Ch contain the hard drive types for hard drives 1 and 2 of
the secondary controller.
Configuration Byte 1Dh, Enhanced IDE Hard Drive Support
Default Value = F0h
Bit Function
7 EIDE - Drive C (83h)
6 EIDE - Drive D (82h)
5 EIDE - Drive E (81h)
4 EIDE - Drive F (80h)
3..0 Reserved
Values for bits <7..4> :
0 = Disable
1 = Enable for auto-configure
Configuration Byte 1Fh, Power Management Functions
Default Value = 00h
Bit Function
7..4 Reserved
3 Slow Processor Clock for Low Power Mode
0 = Processor runs at full speed
1 = Processor runs at slow speed
2 Reserved
1 Monitor Off Mode
0 = Turn monitor power off after 45 minutes in
standby
1 = Leave monitor power on
0 Energy Saver Mode Indicator (Blinking LED)
0 = Disable
1 = Enable
Configuration Byte 24h, System Board Identification
Default Value = 7Eh
Configuration memory location 24h holds the system board ID.
Configuration Byte 25h, System Architecture Data
Default Value = 0Bh
Bit Function
7..4 Reserved
3 Unmapping of ROM:
0 = Allowed
1 = Not allowed
2 Reserved
1,0 Diagnostic Status Byte Address
00 = Memory locations 80C00000h-80C00004h
01 = I/O ports 878h-87Ch
11 = neither place
Compaq Deskpro and Evo Personal Computers
Featuring Intel Celeron and Pentium III Processors
Fifth Edition – March 2002
4-28
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