Intel XeonTM Processor MP
102
Datasheet
Note:
Writing to a read-command register or reading from a write-command register will produce invalid
results.
The default command after reset is to a reserved value (00h). After reset, “Receive Byte” SMBus
packets will return invalid data until another command is sent to the thermal sensor.
7.4.6
SMBus Thermal Sensor Registers
7.4.6.1
Thermal Reference Registers
Once the SMBus thermal sensor reads the processor thermal diode, it performs an analog to digital
conversion and stores the results in the Thermal Reference Register (TRR). The supported range is
+127 to 0 decimal and is expressed as an eight-bit number representing temperature in degrees
Celsius. This eight-bit value consists of seven bits of data and a sign bit (MSB) where the sign is
always positive (sign = 0) and is shown in
Table 45. The values shown are also used to program the
Thermal Limit Registers.
The value of these registers should be treated as saturating values. Values above 127 are
represented at 127 decimal, and values of zero and below may be represented as 0 to -127 decimal.
If the device returns a value where the sign bit is set (1) and the data is 000_0000 through
111_1110, the temperature should be interpreted as 0
° Celsius.
7.4.6.2
Thermal Limit Registers
The SMBus thermal sensor has four Thermal Limit Registers; RRHL is used to read the high limit,
RRLL is read for the low limit, WRHL is used to write the high limit, and the WRLL to write the
low limit. These registers allow the user to define high and low limits for the processor core
thermal diode reading. The encoding for these registers is the same as for the Thermal Reference
Register shown in
Table 45. If the processor thermal diode reading equals or exceeds one of these
limits, then the alarm bit (RHIGH or RLOW) in the Thermal Sensor Status Register is triggered.
7.4.6.3
Status Register
The Status Register shown in
Table 46 indicates which (if any) thermal value thresholds for the
processor core thermal diode have been exceeded. It also indicates if a conversion is in progress or
if an open circuit has been detected in the processor core thermal diode connection. Once set, alarm
bits stay set until they are cleared by a Status Register read. A successful read to the Status Register
Table45. Thermal ReferenceRegisterValues
Temperature
(°C)
Register Value
(binary)
+127
0 111 1111
+126
0 111 1110
+100
0 110 0100
+50
0 011 0010
+25
0 001 1001
+1
0 000 0001
0
0 000 0000