PIIX datasheet(108/122 Pages) INTEL

108 / 122 page

82371FB (PIIX) AND 82371SB (PIIX3)

108

3.12.

Power Management

The PIIX/PIIX3 has extensive power management capability permitting a system to operate in a low power

state without being powered down. In a typical desktop personal computer there are two states — Power On

and Power-Off. Leaving a system powered on when not in use wastes power. The PIIX/PIIX3 provides a Fast

On/Off feature that creates a third state called Fast Off (Figure 10). When in the Fast Off state, the system

consumes less power than the Power-On state.

The PIIX's power management architecture is based on three functions—System Management Mode (SMM),

Clock Control, and Advanced Power Management (APM). Software (called SMM code) controls the

transitions between the Power On state and the Fast Off state. The PIIX/PIIX3 invokes this software by

generating an SMI to the CPU (asserting the SMI# signal). A variety of programmable events are provided

that can generate an SMI. The SMM code places the system in either the Power On state or the Fast Off

state.

A Fast On event is an event that instructs the computer (via an SMI to the CPU) to enter the Power-On state

in anticipation of system activity by the user. Fast On events are programmable and include moving the

mouse, pressing a key on the keyboard, an external hardware event, an incoming call to a system

FAX/Modem, a RTC alarm, or the operating system.

Fast Off

Power Switch

Turned On

Fast Off Event

(Timer Expires,

EXTSMI#,

RTC Alarm,

APM Call)

Power Switch

Turned Off

Fast On Event

(Mouse, Keyboard,

ComPort Activity,

EXTSMI#, RTC Alarm,

APM Call)

Power Switch

Turned Off

Power

Off

051905_3.drw

051905

Figure 10. Fast On/Off Flow

PIIX Scheda tecnica(PDF) 108 Page - Intel Corporation