AN2202

3 STR73x low power modes

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3 FREEN is bit 7 in register PRCCU_PLLCR, in the same register the DX(2:0) must be all sets in

order to provide the PLL slow frequency.

3.2.2

WFI mode

To enter WFI mode, you must clear the WFI bit in the PRCCU_SMR register.

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

3.2.3

LPWFI mode

To enter LPWFI mode you have to:

1.

Select the clock which will be used by peripherals during LPWFI: RC or external oscillator

with the CMU (CKSEL0 bit in the CMU_CTRL register), this clock can be set as running

low (with RCFR bit in CMU_CTRL register)

2.

During the LPWFI, the clock used will be divided by 16: CLK2/16 (WFI_CKSEL bit of the

PRCCU_CCR register)

3.

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

4.

Write 0 in the WFI bit of the PRCCU_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 VRLPW in the PRCCU_VRCTR

register.

●

In LPWFI, the FLASH module should enter Power Down mode by setting the LPS bit of

FLASH CR0 register status.

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, the original MCLK clock configuration must be restored by software.

3.2.4

STOP mode

To enter STOP mode you have to:

1.

Configure at least one external wake-up line or WUT to wake-up the MCU from STOP

mode. (Refer to the WIU & WUT section in the STR73x reference manual)

2.

Reset the STOP bit in register WIU_CTRL and the STOP_I bit in the PRCCU_CFR

register.

3.

To enter STOP mode, write the sequence 1, 0, 1 to the STOP bit in the WIU_CTRL

register.

4.

In order to avoid executing any valid instructions after a STOP bit setting sequence and

before entering STOP mode, it is mandatory to execute a few (at least 6) dummy

instructions after the STOP bit setting sequence.

5.

To be sure that STOP mode was really entered, immediately after the end of the STOP bit

setting sequence (including the dummy instructions), poll the PRCCU STOP_I flag bit and

the STOP bit (WIU_CTRL register). If the STOP bit setting sequence has been correctly

executed, these bits must be STOP_I = 1 and STOP = 0. If it is not the case you must

restart all the sequence from the beginning.

6.

When exiting STOP mode, clear the pending wake up interrupt line (WIU_PR register).