ST7265X datasheet(47/166 Pages) STMICROELECTRONICS

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ST7265x

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8 POWER SAVING MODES

8.1 INTRODUCTION

To give a large measure of flexibility to the applica-

tion in terms of power consumption, two main pow-

er saving modes are implemented in the ST7.

After a RESET the normal operating mode is se-

lected by default (RUN mode). This mode drives

the device (CPU and embedded peripherals) by

means of a master clock which is based on the

main oscillator frequency divided by 2 (fCPU).

From Run mode, the different power saving

modes may be selected by setting the relevant

instruction whose action depends on the oscillator

status.

The user can also switch off any unused on-chip

peripherals

individually

programming

the

MISCR2 register.

8.2 WAIT MODE

WAIT mode places the MCU in a low power con-

sumption mode by stopping the CPU.

This power saving mode is selected by calling the

“WFI” ST7 software instruction.

All peripherals remain active. During WAIT mode,

the I1:0] bits in the CC register are forced to 0, to

enable all interrupts. All other registers and mem-

ory remain unchanged. The MCU remains in WAIT

mode until an interrupt or Reset occurs, whereup-

on the Program Counter branches to the starting

address of the interrupt or Reset service routine.

The MCU will remain in WAIT mode until a Reset

or an Interrupt occurs, causing it to wake up.

Refer to Figure 33.

Figure 33. WAIT Mode Flow Chart

WFI INSTRUCTION

RESET

INTERRUPT

CPU CLOCK

OSCILLATOR

PERIPH. CLOCK

I1:0] BITS

CLEARED

OFF

CPU CLOCK

OSCILLATOR

PERIPH. CLOCK

I1:0] BITS

SET

FETCH RESET VECTOR

OR SERVICE INTERRUPT

DELAY

IF RESET

Note: Before servicing an interrupt, the CC

set during the interrupt routine and cleared

when the CC register is popped.

(Refer to Figure 20 and

Figure 21)

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