2 System Board

Chip-Set

 

described on page 37.

 

RTC

The real-time clock (RTC) is 146818A-compatible. With an accuracy of

 

20 ppm (parts per million). The configuration RAM is implemented as 256

 

bytes of CMOS memory.

 

Serial EEPROM

This is the non-volatile memory which holds the default values for the CMOS

 

memory (in the event of battery failure, or the user pressing

in Setup).

General Purpose I/O There are several general purpose I/O pins. Some of these are used on the HP Vectra to sense the current settings of system board switches (page 31 and page 39).

Description

GPIO number

 

 

Reserved (HP security from Little Ben IRQ)

GPIO10

 

 

Ratio of processor frequency to processor local bus frequency (as per SW-4)

GPIO11

 

 

Auto soft lock

GPIO12

 

 

Backplane identification BPID0 (always =0); (see BPID1, below)

GPIO13

 

 

Host bus frequency selection, as indicated by SW-1

GPIO14

 

 

Host bus frequency selection, as indicated by SW-2

GPIO15

 

 

Serial EEPROM clear (as per SW-6)

GPIO16

 

 

Ratio of processor frequency to processor local bus frequency (as per SW-3)

GPIO17

 

 

Backplane identification BPID1 (desktop=1, minitower=0)

GPIO20

 

 

Serial EEPROM data out

GPIO21

 

 

Serial EEPROM data in

GPIO22

 

 

Serial EEPROM clock

GPIO23

 

 

Serial EEPROM chip select

GPIO24

 

 

Reserved (for fax or general purpose light)

GPIO25

 

 

27