Intel Pentium 4 Processor on 90 nm Process Thermal and Mechanical Design Guidelines

Thermal Requirements
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26 Intel
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Pentium
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4 on 90 nm Process Thermal Design Guide
Figure 7. Concept for Clocks under Thermal Monitor Control
PROCHOT#
Resultant
internal clock
N
ormal cloc
k
Internal clock
Duty cycle
control
3.4.3 Bi-Directional PROCHOT#
The Pentium 4 processor on 90 nm process implements a bi-directional PROCHOT# capability to
allow system designs to protect various components from over-temperature situations. The
PROCHOT# signal is bi-directional in that it can either signal when the processor has reached its
maximum operating temperature or be driven from an external source to activate the TCC. The
ability to activate the TCC via PROCHOT# can provide a means for thermal protection of system
components.
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) and activating 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# only as a
backup in case of system cooling failure.
3.4.4 Operation and Configuration
To maintain compatibility with previous generations of processors, which have no integrated
thermal logic, the thermal control circuit portion of Thermal Monitor is disabled by default.
During the boot process, the BIOS must enable the thermal control circuit; or a software driver
may do this after the operating system has booted. Thermal Monitor must be enabled to ensure
proper processor operation.
The thermal control circuit feature can be configured and monitored in a number of ways. OEMs
are expected to enable the thermal control circuit while using various registers and outputs to
monitor the processor thermal status. The thermal control circuit is enabled by the BIOS setting a
bit in an MSR (Model Specific Register). Enabling the thermal control circuit allows the
processor to attempt to maintain a safe operating temperature without the need for special
software drivers or interrupt handling routines. When the thermal control circuit has been