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2 System Board
Devices on the SM Bus
Devices on the SM Bus
The System Management (SM) bus is used to monitor several of the
hardware functions (such as voltage levels, temperature, fan speed, DIMM
presence and type) of the motherboard. It is controlled by the SM bus
controller located in the PIIX4 chip.
Serial EEPROM
This is the non-volatile memory which holds the default values for the CMOS
memory (in the event of battery failure).
The computer uses 4 Kbit of Serial EEPROM implemented within a single
512 ✕ 8-bit ROM chip. Serial EEPROM is ROM in which one byte at a time
can be returned to its unprogrammed state by the application of appropriate
electrical signals. In effect, it can be made to behave like very slow, non-
volatile RAM. It is used for storing the tatoo string, the serial number, and
the parameter settings for the Setup program.
When installing a new system board, the Serial EEPROM will have a blank
serial number field. This will be detected automatically by the BIOS, which
will then prompt the user to enter the serial number which is printed on the
identification label on the back of the computer.
Device SM Bus Address
PIIX4 SM Bus Master 10
Serial EEPROM A8, AA, AC, AE
LM75 90
LM78 5A
SDRAM slot 1 A0
SDRAM slot 2 A2
SDRAM slot 3 A4
SDRAM slot 4 A6
PLL D2
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