LGA775 Socket Heatsink Loading
32
Thermal and Mechanical Design Guidelines
4.2.1
PROCHOT# Signal
The primary function of the PROCHOT# signal is to provide an external indication that
the processor has exceeded its maximum operating temperature. While PROCHOT# is
asserted, the TCC will be active. Assertion of the PROCHOT# signal is independent of
any register settings within the processor. It is asserted any time the processor die
temperature reaches the trip point.
PROCHOT# can be configured via BIOS as an output or bi-directional signal. As an
output, PROCHOT# will go active when the processor temperature of either core
exceeds its maximum operating temperature. This indicates the TCC has been
activated. As an input, assertion of PROCHOT# will activate the TCC for both cores.
The TCC will remain active until the system de-asserts PROCHOT#
The temperature at which the PROCHOT# signal goes active is individually calibrated
during manufacturing. The power dissipation of each processor affects the set point
temperature. The temperature where PROCHOT# goes active roughly parallels the
thermal profile. Once configured, the processor temperature at which the PROCHOT#
signal is asserted is not re-configurable.
One application is the thermal protection of voltage regulators (VR). System
designers can create a circuit to monitor the VR temperature and activate the TCC
when the temperature limit of the VR is reached. By asserting PROCHOT# (pulled-
low) or FORCEPR#, which activates the TCC, the VR can cool down as a result of
reduced processor power consumption. Bi-directional PROCHOT# can allow VR
thermal designs to target maximum sustained current instead of maximum current.
Systems should still provide proper cooling for the VR, and rely on bi-directional
PROCHOT# signal only as a backup in case of system cooling failure.
Note:
A thermal solution designed to meet the thermal profile targets should rarely
experience activation of the TCC as indicated by the PROCHOT# signal going active.
4.2.2
Thermal Control Circuit
The Thermal Control Circuit portion of the Thermal Monitor must be enabled for the
processor to operate within specifications. The Thermal Monitor’s TCC, when active,
will attempt to lower the processor temperature by reducing the processor power
consumption. In the original implementation of thermal monitor this is done by
changing the duty cycle of the internal processor clocks, resulting in a lower effective
frequency. When active, the TCC turns the processor clocks off and then back on with
a predetermined duty cycle. The duty cycle is processor specific, and is fixed for a
particular processor. The maximum time period the clocks are disabled is ~3
μ
s. This
time period is frequency dependent and higher frequency processors will disable the
internal clocks for a shorter time period. Figure 8 illustrates the relationship between
the internal processor clocks and PROCHOT#.
Performance counter registers, status bits in model specific registers (MSRs), and the
PROCHOT# output pin are available to monitor the Thermal Monitor behavior.
Summary of Contents for QX68000 Core 2 Extreme
Page 30: ...LGA775 Socket Heatsink Loading 30 Thermal and Mechanical Design Guidelines...
Page 74: ...Heatsink Clip Load Metrology 74 Thermal and Mechanical Design Guidelines...
Page 76: ...Thermal Interface Management 76 Thermal and Mechanical Design Guidelines...
Page 96: ...Case Temperature Reference Metrology 96 Thermal and Mechanical Design Guidelines...
Page 108: ...Legacy Fan Speed Control 108 Thermal and Mechanical Design Guidelines...
Page 112: ...BTX System Thermal Considerations 112 Thermal and Mechanical Design Guidelines...
