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64-bit Intel
Xeon Processor MP with up to 8MB L3 Cache Datasheet
115
Features
2. The shaded bits are transmitted by the thermal sensor, and the bits that aren’t shaded are transmitted by the
SMBus host controller.
All of the commands in
Table 8-10
are for reading or writing registers in the SMBus thermal
sensor, except the one-shot command (OSHT) register. The one-shot command forces the
immediate start of a new conversion cycle. If a conversion is in progress when the one-shot
command is received, then the command is ignored. If the thermal sensor is in stand-by mode when
the one-shot command is received, a conversion is performed and the sensor returns to stand-by
mode. The one-shot command is not supported when the thermal sensor is in auto-convert mode.
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.
8.4.6
SMBus Thermal Sensor Registers
8.4.6.1
Thermal Value 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
Table 8-10. SMBus Thermal Sensor Command Byte Bit Assignments
Register
Command
Reset State
Function
RESERVED
00h
RESERVED
Reserved for future use
TRR
01h
0000 0000
Read processor core thermal diode
RS
02h
N/A
Read status byte (flags, busy signal)
RC
03h
00XX XXXX
Read configuration byte
RCR
04h
0000 0010
Read conversion rate byte
RESERVED
05h
RESERVED
Reserved for future use
RESERVED
06h
RESERVED
Reserved for future use
RRHL
07h
0111 1111
Read processor core thermal diode T
HIGH
limit
RRLL
08h
1100 1001
Read processor core thermal diode T
LOW
limit
WC
09h
N/A
Write configuration byte
WCR
0Ah
N/A
Write conversion rate byte
RESERVED
0Bh
RESERVED
Reserved for future use
RESERVED
0Ch
RESERVED
Reserved for future use
WRHL
0Dh
N/A
Write processor core thermal diode T
HIGH
limit
WRLL
0Eh
N/A
Write processor core thermal diode T
LOW
limit
OSHT
0Fh
N/A
One shot command (use send byte packet)
RESERVED
10h – FFh
N/A
Reserved for future use