2021-12-10 10:38 AM
Bottom of page 299 in the H7 Ref Manual says pretty clearly that "In Standby, all I/O pins are high impedance without pull" except for a few WKUPs and Reset. Okay, this sounds like I'm out of luck for holding peripherals in low power states. But there's a STMicro .pptx out there called "Presentation of the STM32H7 Power Controller" page 28 about Standby "Each I/O can be configured with or without pullup or pulldown, which is applied and released thanks to the APC control bit". These two docs appear to directly contradict each other, or am I missing something? I'm guessing the .pptx is wrong, and might be a holdover from the STM32L series. The .pptx refers to an "APC control bit" that I can't find mentioned anywhere else. Can anyone help me resolve this? Thanks!
The .pptx is here:
2021-12-10 01:03 PM
They just copy/pasted the presentation and didn't fact check it very well. Appears to be directly copied from an STM32WB presentation. No such functionality on the STM32H7.
If things directly contradict the RM, generally the RM is correct.
2021-12-10 01:38 PM
Maybe copy/paste from 'L4, where PWR_CR3.APC is a thing. Or a planned feature not implemented for whatever reason. Or maybe it's even implemented, but was too buggy so ST simply omitted its description from RM.
In any case, if it's not in RM, it is as good as nonexistent.
JW
2021-12-10 03:49 PM
Huge thanks TDK and JW! That was my guess, but I didn't want to pass over a valuable feature. Now I gotta sprinkle a bunch of physical resistors all over the place, likely have to add more power rail controls..., argh. Oh well, life with ST I guess, it's otherwise a pretty kick-*** little ARM, so far. Thanks! -db
2021-12-10 06:13 PM
There are other low power states where pullups can be active, if you can get away with using a little more power.