AN2100

STR71x low power modes

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4.2.2

WAIT For Interrupt mode (WFI)

To enter WFI mode, you must write a ‘0’ in the WFI bit of the RCCU_SMR register.

To wakeup from WFI mode an interrupt request must be acknowledged by the EIC.

4.2.3

Low Power WAIT For Interrupt mode (LPWFI)

To enter LPWFI mode you have to:

1.

Select the clock to be used by peripherals during LPWFI: CLK2/16 or CK_AF

(WFI_CKSEL bit of the RCCU_CCR register)

2.

Select LPWFI mode by setting the LPOWFI bit in the RCCU_CCR register.

3.

Write 0 in the WFI bit of the RCCU_SMR register to enter LPWFI mode

Like WFI mode, to wakeup from LPWFI mode an interrupt request must be acknowledged

by the EIC.

To further reduce MCU power consumption in LPWFI mode you can:

●

Stop the Main voltage regulator (MVR) by setting bit LPVRWFI in the PCU_PWRCR

register.

●

Put the FLASH in power-down mode by setting bit PWD in the FLASH_CR0 register

(refer to the STR7 Flash programming reference manual)

●

When selecting the CK_AF(32 kHz) as system clock, you can reduce power

consumption by stopping the external oscillator during LPWFI using a GPIO pin.

Note:

1

After exit from LPWFI mode, the Flash and the main voltage regulator are re-enabled

automatically if they were switched off during the low power mode.

2

After wakeup from LPWFI mode, if the clock selected during LPWFI mode is CK2_16, the

system clock (RCLK) switches automatically to CK2.

After wakeup from LPWFI mode, if the clock selected during LPWFI mode is CK_AF, this

clock remains the system clock (RCLK).

3

Refer to Figure 4 and Figure 5 for examples.