L9805 datasheet(24/103 Pages) STMICROELECTRONICS

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L9805

3.7 POWER SAVING MODES

3.7.1 Introduction

There are three Power Saving modes. The Slow

Mode may be selected by setting the relevant bits

in the Miscellaneous register as detailed in Section

3.4. Wait and Halt modes may be entered using

the WFI and HALT instructions.

3.7.2 Slow Mode

In Slow mode, the oscillator frequency can be di-

vided by 4, 8, 16 or 32 rather than by 2. The CPU

and peripherals (except CAN, see Note) are

clocked at this lower frequency. Slow mode is

used to reduce power consumption.

Note: Before entering Slow mode and to guaran-

tee low power operations, the CAN Controller

must be placed by software in STANDBY mode.

3.7.3 Wait Mode

Wait mode places the MCU in a low power con-

sumption mode by stopping the CPU. All peripher-

als remain active. During Wait mode, the I bit (CC

All other registers and memory remain un-

changed. The MCU will remain in Wait mode until

an Interrupt or Reset occurs, whereupon the Pro-

gram 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 (coming from CAN, Timers 1 & 2,

EEPROM, ADC, PWM 1 & 2, I/O ports peripherals

and Power Bridge) occurs, causing its wake-up.

Refer to Figure 12 below.

Figure 12. Wait Mode Flow Chart

WAIT INSTRUCTION

RESET

FETCH RESET VECTOR

OR SERVICE INTERRUPT

INTERRUPT

CPU CLOCK

OSCILLATOR

PERIPH. CLOCK

I-BIT

SET

CPU CLOCK

OSCILLATOR

PERIPH. CLOCK

I-BIT

CLEARED

OFF

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