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Datasheet

Thermal Specifications and Design Considerations

The PROCHOT# signal is asserted when a high temperature situation is detected,

regardless of whether Thermal Monitor or Thermal Monitor 2 is enabled.

Note that the Thermal Monitor 2 TCC cannot be activated via the on demand mode. The

Thermal Monitor TCC, however, can be activated through the use of the on demand

mode.

5.2.3

On-Demand Mode

The processor 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 Thermal Monitor feature. On-Demand mode is

intended as a means to reduce system level power consumption. Systems using the

Pentium 4 processor 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 immediately reduces 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 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.

Figure 15.

Thermal Monitor 2 Frequency and Voltage Ordering

VID

Frequency

Temperature

TM2

MAX

TM2

VID

TM2

PROCHOT#

641 Datasheet(PDF) 81 Page - Intel Corporation