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Revision 1.2

2.0

Power, Reset and Clocks

2.1

POWER

2.1.1

Power Planes

The PC8741x devices have three power planes (wells), as shown in the table below:

Table 4. Power Planes

For correct operation, either VSB or VBAT must be applied whenever VDD is applied.

2.1.2

Power States

The PC8741x devices have four power states:

• Battery Fail - the Main, Standby and Backup power planes are all powered off (V

DD, VSB and VBAT are inactive).

• Power Fail - the Main and Standby power planes are powered off; the Backup power plane is on (V

DD and VSB are

inactive; VBAT is active).

• Power Off - the Main power plane is powered off; the Standby power plane is on; the Backup power plane is on (V

is inactive; VSB is active; VBAT is irrelevant).

• Power On - the Main and Standby power planes are powered on; the Backup power plane may is on (V

DD and VSB

are active; VBAT is irrelevant).

The following power state is illegal:

• The Main power plane is powered on, the Standby power plane is off and the Backup power plane is on or off (i.e., V

is active, VSB is inactive and VBAT is irrelevant).

The following table summarizes the power states described above.

Power Plane

Description

Power Pins

Ground Pins

Main

Powers the Legacy modules (Serial Ports, Parallel Port,

FDC, KBC), the LPC Interface, part of the Conﬁguration

Control and some external signals1

1. See the tables in Section 1.4 (pages 23-30), speciﬁcally the Power Well column.

VDD

VSS

Standby

Powers the ACCESS.bus and X-Bus Interfaces, the GPIO

ports, the Clock Generator, part of the SWC, part of the

Conﬁguration Control and some external related signals1

VSB

VSS

Backup

Powers the RTC, the 32.768 KHz clock/crystal oscillator,

part of the SWC and some functions that must be

preserved at all times1

VPP

2. VPP is an internal power signal derived from VSB or VBAT.VPP is taken from VSB if it is greater than

the minimum value defined in Section 11.1.5; otherwise it is taken from VBAT. For more

details on switching between them, refer to Section 8.2.9.

VSS

Table 5. Power States and Related Power Planes

Power State

Main (VDD)

Standby (VSB)

Backup (VPP)VBAT

Battery Fail

Off

Power Fail

Off

Power Off

Off

On or Off

Power On

On or Off

Illegal1

1. Operation is not guaranteed and register data may be corrupted.

Off

On or Off

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