PC87570-ICCSLASHVUL datasheet(79/168 Pages) NSC

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Power Mode Control (PMC)

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8.0

Power Mode Control (PMC)

The PMC improves the efficiency of PC87570 operation by

adjusting its power consumption to the level of performance

the application requires.

8.1

FEATURES

• Three power modes:

— Active

— Idle

— Power Off

• Power mode switch, software and/or hardware controlled

• High Frequency Clock Generator (HFCG) enable/dis-

able control

8.2

THE POWER MODES

Table 8-1 summarizes the main properties of the three

modes.

Table 8-1. Power Mode Summary

Active Mode

In Active mode, the PC87570 operates at the frequency

generated by the HFCG. You can reduce power consump-

tion in this mode by selectively disabling modules with their

respective Enable/Disable bits or when executing a WAIT

instruction while IDLE or EIM (bits 2 and 5) in the PMCR

stops executing new instructions until it receives an inter-

rupt signal.

After reset, the PC87570 is in Active mode.

Idle Mode

In Idle mode, the clock is stopped for most of the PC87570.

Only the PMC and a limited number of other modules con-

tinue to operate at the 32.768 KHz clock rate; they can

wake-up the PC87570 and resume instruction execution

when required.

Details of module activity in Idle mode are included in the

relevant chapters for each module.

Power Off Mode

When power is turned off, the PC87570 reaches its lowest

activity level. The content of the memories and registers is

not preserved in this mode.

A battery supply pin (VBAT) provides power to the RTC, al-

lowing it to continue functioning even in Power Off mode.

Refer to Chapter 6 for the RTC features supported by bat-

tery backup.

1. With respect to the DHF bit in the Power

Mode Control Register (PMCR)

2. Supports certain RTC features

8.3

SWITCHING BETWEEN POWER MODES

Switching from one mode to another is accomplished by us-

ing the protocols described below. Figure 8-1 depicts the

transitions between the power modes when the EIM bit of

the PMCR Register is set.

8.3.1

Decreasing Power Consumption

Enter Idle mode by setting the EIM and IDLE bits of the

PMCR Register, and then executing the WAIT instruction.

To further reduce power consumption, you can disable the

HFCG by setting the DHF bit of the PMCR Register before

executing the WAIT instruction.

Enter Power Off mode by turning off the power to the VCC

pins of the PC87570.

The PFAIL input, which is the non-maskable interrupt (NMI)

source, may be used to interrupt the PC87570 to complete

content saving to a non-volatile memory and to stop write

operations to the RTC, before power to the PC87570 is dis-

connected.

8.3.2

Increasing Performance

Wake-Up from Idle mode to Active is a hardware wake-

up event that causes the PC87570 to switch directly from

Idle mode to Active mode. The core resumes operation by

executing an interrupt routine. A wake-up event may have

one of three sources:

A maskable event (from MIWU)

An NMI

An ISE interrupt in Dev environment only.

The wake-up is identified by a high level on the maskable

event, and a high to low transition on the NMI or ISE interrupts.

Once a wake-up event is detected, it is latched until an inter-

rupt acknowledge bus cycle is detected, or reset is applied.

One exception is the wake-up on host transaction, which caus-

es the core to continue executing the WAIT instruction until an

interrupt occurs.

Waking up to Active mode clears the IDLE bit of the PMCSR

Exit from Power Off and resume activity in Active mode by

applying power to the PC87570 (VCC). The power-up reset

sequence described in Section 2.3 on page 26 is used.

Mode

HFCG

CLK

Power

Active

Idle

On or Off1

Off

Power Off

Off

Battery backup only2

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