Mobile Intel Pentium 4 Processor with 533 MHz Front Side Bus
68 Mobile Intel
®
Pentium
®
4 Processor with 533 MHz System Bus Datasheet
Thermal Specifications and Design Considerations
cause a noticeable performance loss, and in some cases may result in a T
C
that exceeds the
specified maximum temperature and may affect the long-term reliability of the processor. In
addition, a thermal solution that is significantly under designed may not be capable of cooling the
processor even when the TCC is active continuously. Refer to the Mobile Intel
®
Pentium
®
4
Processor Thermal Design Guidelines for Transportable Systems for information on designing a
thermal solution.
The duty cycle for the TCC, when activated by the Intel Thermal Monitor, is factory configured
and cannot be modified. The Intel Thermal Monitor does not require any additional hardware,
software drivers, or interrupt handling routines.
5.2.2 On-Demand Mode
The mobile Intel Pentium 4 processor with 533 MHz FSB provides an auxiliary mechanism that
allows system software to force the processor to reduce its power consumption. This mechanism is
referred to as "On-Demand" mode and is distinct from the Intel Thermal Monitor feature. On-
Demand mode is intended as a means to reduce system level power consumption. Systems utilizing
the mobile Intel Pentium 4 processor with 533 MHz FSB must not rely on software usage of this
mechanism to limit the processor temperature.
If bit 4 of the ACPI P_CNT Control register (located in the processor IA32_THERM_CONTROL
MSR) is written to a 1, the processor will immediately reduce its power consumption via
modulation (starting and stopping) of the internal core clock, independent of the processor
temperature. When using On-Demand mode, the duty cycle of the clock modulation is
programmable via bits 3:1 of the same ACPI P_CNT Control register. In On-Demand mode, the
duty cycle can be programmed from 12.5% on/ 87.5% off, to 87.5% on/12.5% off in 12.5%
increments. On-Demand mode may be used in conjunction with the Intel Thermal Monitor. If the
system tries to enable On-Demand mode at the same time the TCC is engaged, the factory
configured duty cycle of the TCC will override the duty cycle selected by the On-Demand mode.
5.2.3 PROCHOT# Signal Pin
An external signal, PROCHOT# (processor hot), is asserted when the processor die temperature
has reached its maximum operating temperature. If the Intel Thermal Monitor is enabled (note that
the Intel Thermal Monitor must be enabled for the processor to be operating within specification),
the TCC will be active when PROCHOT# is asserted. The processor can be configured to generate
an interrupt upon the assertion or deassertion of PROCHOT#. Refer to the Intel Architecture
Software Developer's Manuals and Intel NetBurst micro-architecture BIOS Writer’s Guide for
specific register and programming details.
The mobile Intel Pentium 4 processor with 533 MHz FSB 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