Clock Control And Low Power States - Intel Pentium II Developer's Manual

ELECTRICAL SPECIFICATIONS
7.2.

CLOCK CONTROL AND LOW POWER STATES

The Pentium II processor allows the use of AutoHALT, Stop-Grant, Sleep and Deep Sleep
states to reduce power consumption by stopping the clock to internal sections of the
processor, depending on each particular state. See Figure 7-2 for a visual representation of
the Pentium II processor low power states.
2. Auto HALT Power Down State
BCLK running.
Snoops and interrupts allowed.
Snoop Snoop
Event Event
Occurs Serviced
4. HALT/Grant Snoop State
BCLK running.
Service snoops to caches.
For the processor to fully realize the low current consumption of the Stop-Grant, Sleep and
Deep Sleep states, a Model Specific Register (MSR) bit must be set. For the MSR at 02AH
(Hex), bit 26 must be set to a '1' (this is the power on default setting) for the processor to
stop all internal clocks during these modes.
7-2
HALT Instruction
INIT#, BINIT#, INTR, NMI,
SMI#, RESET#
Snoop Event Occurs
Snoop Event Serviced
Figure 7-2. Stop Clock State Machine
1. Normal State
Normal execution.
STPCLK# STPCLK#
Asserted De-asserted
3. Stop Grant State
BCLK running.
Snoops and interrupts allowed.
SLP# SLP#
Asserted De-asserted
5. Sleep State
BCLK running.
No snoops or interrupts allowed.
BCLK BCLK
Input Input
Stopped Restarted
6. Deep Sleep State
BCLK stopped.
No snoops or interrupts allowed.
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