Using Stop or Standby Mode on STM32L072 (Murata CMWX1ZZABZ-078) Without External RTC

[TAHIR97]

Hello,

I am working with the CMWX1ZZABZ-078 Murata module, which includes the STM32L072 MCU. I want to implement low-power modes to reduce current consumption.

Specifically, I am interested in using either Stop mode or Standby mode. However, I would like to know if it is possible to enter these modes without having an external RTC connected.

Is it mandatory to use an external RTC to wake up the MCU from these modes, or can it be done using internal clocks or other peripherals?

Any guidance or examples would be greatly appreciated.

Thank you!

[MM..1]

No all low power modes is possible with internal RTC.

[TDK]

Both modes can be entered without the RTC enable or an external RTC crystal.

To wake up from stop mode, there are a lot of peripherals that can be used to wake up the device. These are covered in the reference manual. Most of them.

To wake up from standby mode, the only non-RTC internal clock that can be used is IWDG. External inputs on NRST or wakeup pins could also work.

*rm0376-ultralowpower-stm32l0x2-advanced-armbased-32bit-mcus-stmicroelectronics.pdf

[TAHIR97]

I don't understand how to use the IWDG to exit Stop mode. Can you explain how the Independent Watchdog (IWDG) can be used to wake up the MCU from Stop mode?

[TDK]

 When the IWDG expires, it triggers a system reset by pulling NRST low, which wakes up the chip. That is typically not how you want to exit stop mode.