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I have a fairly simple question that I can't find the answer to in the datasheet or reference manual for an STM32L073RZ. Put simply: is there a mechanism within the processor that prevents entering Standby mode with WKUP pins enabled when the voltage supplied to either of those pins is greater than or equal to logic high?

I ask because this is the behaviour I'm observing but, as previously stated, can't find mention of this in any documentation.

I currently have a board whereby the GPO of an NFC EEPROM (M24SR64-YMN6T/2) is attached to a WKUP pin. The GPO is active low and configured for SESSION OPENED mode. This means that the GPO line usually sits high, but, when an RF session is underway, will go low. When the RF session is finished the line pulls high again and would trigger a WKUP. This is the intended outcome, at least.

However, as I've already mentioned, I believe that the GPO line being high is preventing the processor from going into Standby mode. If this is the case it's a simple hardware fix, but I just want to make sure that I'm not missing anything.

I should mention that, if I disconnect the GPO line from the WKUP pin the processor goes into Standby mode as expected. I should also mention that, if I drive the WKUP line high from another source then it seems to prevent Standby mode. Lastly, if I have the GPO line connected to the WKUP pin but pulled low externally, then the processor goes into Standby mode.

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Take a look at the comment at the bottom of page 170 of the reference manual:

Note: An additional wakeup event is detected if the WKUP pins are enabled (by setting the EWUPx (x=1, 2, 3) bits) when the WKUP pin levels are already high

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  • \$\begingroup\$ Thanks, I'd missed that. Unfortunately, clearing the CWUF bit after enabling the wakeup pins but before sleeping still leads to increased power consumption. \$\endgroup\$ – Adam Mitchell Jul 12 at 14:18

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