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Datasheet 87
System Management Feature Specifications
THRMALERT# signal (see Section 6.1.1 for more details). At power up, the appropriate alarm
register values need to be programmed into the thermal sensing device via the SMBus. It is
recommended that the upper thermal reference threshold byte (provided in the processor
information ROM) be used for setting the upper threshold value in the alarm register.
When polling the thermal sensing device on the processor to read the processor temperatures, it is
recommended that the polling frequency be every 0.5 to 1 second.
6.6 Thermal Sensing Device Supported SMBus
Transactions
The thermal sensing device responds to five of the SMBus packet types: write byte, read byte, send
byte, receive byte, and alert response address (ARA). The send byte packet is used for sending one-
shot commands only. The receive byte packet accesses the register commanded by the last read
byte packet. If a receive byte packet was preceded by a write byte or send byte packet more
recently than a read byte packet, then the behavior is undefined. Table 6-8 through Table 6-12
diagram the five packet types. In these tables, ‘S’ represents the SMBus start bit, ‘P’ represents a
stop bit, ‘Ack’ represents an acknowledge, and ‘///’ represents a negative acknowledge. The shaded
bits are transmitted by the thermal sensor and the unshaded bits are transmitted by the SMBus host
controller. Table 6-13 shows the encoding of the command byte.
Table 6-8. Write Byte SMBus Packet
S Address Write Ack Command Ack Data Ack P
17 bits 1 18 bits18 bits11
Table 6-9. Read Byte SMBus Packet
S Address Write Ack Command Ack S Address Read Ack Data /// P
17 bits 1 18 bits1 1 7 bits 1 1 8 bits 1 1
Table 6-10. Send Byte SMBus Packet
S Address Write Ack Command Ack P
17 bits 1 18 bits1
Table 6-11. Receive Byte SMBus Packet
S Address Read Ack Data /// P
17 bits 1 1 8 bits 1 1
Table 6-12. ARA SMBus Packet
S ARA Read Ack Address /// P
1 0001 100 1 1 1001 1011 1 1