User Manual

Datasheet 15
Pentium
®
III Processor for the PGA370 Socket at 500 MHz to 1.13 GHz
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. For more information, see the Intel Architecture Software Developer’s
Manual, Volume 3: System Programming Guide located on the developer.intel.com website.
2.2.1 Normal State—State 1
This is the normal operating state for the processor.
2.2.2 AutoHALT Powerdown State—State 2
AutoHALT is a low power state entered when the processor executes the HALT instruction. The
processor transitions to the Normal state upon the occurrence of SMI#, INIT#, or LINT[1:0] (NMI,
INTR). RESET# causes the processor to immediately initialize itself.
The return from a System Management Interrupt (SMI) handler can be to either Normal Mode or
the AutoHALT Power Down state. See the Intel Architecture Software Developer's Manual,
Volume III: System Programmer's Guide for more information.
FLUSH# is serviced during the AutoHALT state, and the processor will return to the AutoHALT
state.
Figure 4. Stop Clock State Machine
P
CB757a
2. Auto HALT Power Down State
BCLK running.
Snoops and interrupts allowed.
HALT Instruction and
HALT Bus Cycle Generated
INIT#, BINIT#, INTR,
SMI#, RESET#
1. Normal State
Normal execution.
STPCLK#
Asserted
STPCLK#
De-asserted
3. Stop Grant State
BCLK running.
Snoops and interrupts allowed.
SLP#
Asserted
SLP#
De-asserted
5. Sleep State
BCLK running.
No snoops or interrupts allowed.
BCLK
Input
Stopped
BCLK
Input
Restarted
6. Deep Sleep State
BCLK stopped.
No snoops or interrupts allowed.
4. HALT/Grant Snoop State
BCLK running.
Service snoops to caches.
Snoop Event Occurs
Snoop Event Serviced
Snoop
Event
Occurs
Snoop
Event
Serviced
STPCLK# Asserted
STPCLK# De-asserted
and Stop-Grant State
entered from
AutoHALT
, NMI