PC87365 datasheet(41/215 Pages) NSC

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2.0 Device Architecture and Configuration (Continued)

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ACPI Mode

When the PSC is operated in ACPI mode (bit 0 of the SIOCFD register is set to 1), the ACPI controller of the system controls

the system’s power supply by means of the SLPS3 state. When SLPS3 is set to 0, the power supply turns off; when it is set

to 1, the power supply turns on. The state of the PSON output signal (either ON or OFF) is identical to the state of the SLPS3

input signal. The polarity of PSON is set by the PSONPOL strap.

The only case in which the PSC affects the value of the PSON output is when a Crowbar condition occurs. A Crowbar con-

dition is defined as the state in which PSON has been active for a certain period of time but the system’s power supply re-

mains inactive. In this case, PSON is forced inactive, and the PWBTOUT output is pulsed to indicate to the ACPI controller

that SLPS3 must be driven low, thus indirectly inactivating PSON and preventing a deadlock. For a detailed description of

the Crowbar mechanism, see

Crowbar Condition on the following page(s).

In ACPI mode, during regular operation, the PWBTOUT output is pulsed when either of the following events occurs:

PWBTIN is pulsed.

A wake-up event that is routed to PWBTOUT.

A wake-up event that is routed to the power button output can cause PWBTOUT to be pulsed in ACPI mode if one of the

following conditions is met:

SLPS5 is active.

Enable Power Button Pulse on S3 (bit 3) of the SWC WK_CFG register is set to 1.

However, when in ACPI mode, PWBTIN and PWBTOUT activity has no effect on the PSON output. The power button mech-

anism can have an indirect effect on PSON only if PWBTOUT is connected to the power button input of the ACPI controller,

thus affecting the SLPS3 signal.

Legacy Mode

When the PSC is operated in Legacy mode (bit 0 of the SIOCFD register is set to 0), the PC87365 controls the system’s

power supply. In this mode, the PSON output signal is set by the PC87365 according to the following factors: the state of

input signals, the state of the power supply lines, power button activity and certain configuration bits. Although the ACPI con-

troller does not control the system’s power supply, it tracks the system’s power state. For this purpose, the PC87365 ma-

nipulates the PWBTOUT so that the ACPI controller is always synchronized with the actual state of the PSON output. This

synchronization mechanism assumes that PWBTOUT is connected to the power button input of the ACPI controller. See a

schematic state diagram of the Legacy PSC mechanism in Figure 5.

Figure 5. Legacy Power Supply Control State Diagram

Power

Fail

OFF

Synchronize

ACPI

Check

Resume

Mode

VSB

Power-Up

Reset

VSB Present AND Straps Sampled

Resume AND Last State Is OFF

No Resume AND ACPI Is OFF

No Resume AND ACPI Is ON

Resume AND Last State is ON

Synchronization Done

PWBTOUT Falling Edge

Software Power Supply Off Command

PC87365 Datasheet(PDF) 41 Page - National Semiconductor (TI)

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