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ELECTRICAL SPECIFICATIONS
11.2.
POWER MANAGEMENT: STOP GRANT AND AUTO HALT
The Pentium Pro processor allows the use of Stop Grant and Auto HALT modes to immediately
reduce the power consumed by the device. When enabled, these cause the clock to be stopped
to most of the CPU's internal units and thus significantly reduces power consumption by the
CPU as a whole.
Stop Grant is entered by asserting the STPCLK# pin of the Pentium Pro processor. When STP-
CLK# is recognized by the Pentium Pro processor, it will stop execution and will not service
interrupts. It will continue snooping the bus. Stop Grant power is specified assuming no snoop
hits occur.
Auto HALT is a low power state entered when the Pentium Pro processor executes a halt (HLT)
instruction. In this state the Pentium Pro processor behaves as if it executed a halt instruction,
and it additionally powers-down most internal units. In Auto HALT, the Pentium Pro processor
will recognize all interrupts and snoops. Auto HALT power is specified assuming no snoop hits
or interrupts occur.
The low power standby mode of Stop Grant or Auto HALT can be defined by a configuration
bit to be either the lowest power achievable by the Pentium Pro processor (Stop Grant power),
or a power state in which the clock distribution is left running (Idle power). "Low power stand-
by" disabled leaves the core logic running, while "Low power standby" enabled allows the Pen-
tium Pro processor to enter its lowest power mode. See the EBL_CR_POWERON Model
Specific Register in Appendix C of the Pentium
Operating System Writer's Guide (Order Number 242692-001).
11.3.
POWER AND GROUND PINS
As future versions of the Pentium Pro processor are released, the operating voltage of the CPU
die and of the L2 Cache die may differ from each other. There are two power inputs on the Pen-
tium Pro processor package to support the difference between the two die in the package, and
one 5V pin to support a fan for the OverDrive
package for voltage identification These pins specify the voltage required by the CPU die. This
has been added to cleanly support voltage specification variations on the Pentium Pro processor
and future processors. See Section 11.6., "Voltage Identification" for an explanation of the volt-
age identification (VID) pins.
Future mainstream devices will fall into two groups. Either the CPU die and the L2 Cache die
will both run at the same voltage (V cc P), or the L2 Cache die will use V cc S (3.3V) while the
CPU die runs at another voltage on V cc P. When the L2 Cache die is running on the same supply
as the CPU die, the V cc S pins will consume no current. To properly support this, the system
should distribute 3.3V and a selectable voltage to the Pentium Pro processor socket. Selection
may be provided for by socketed regulation or by using the voltage identification pins. Note that
it is possible that V cc P and V cc S are both nominally 3.3V. It should not be assumed that these
will be able to use the same power supply.
For clean on-chip power distribution, the Pentium Pro processor has 76 V cc (power) and 101V ss
(ground) inputs. The 76 V cc pins are further divided to provide the different voltage levels to
the device. V cc P inputs for the CPU die and some L2 die account for 47 of the V cc pins, while
11-2
®
Pro Family Developer's Manual, Volume 3:
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processor. There are also 4 pins defined on the
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