Nucleo-G474RE: What is the intended use of JP7?

Yoichi Shinoda · ‎2019-07-25

Nucleo-G474RE has JP7, which pulls down BOOT0 pin to ground when a jumper is installed, but this alone does not control boot options. What is the intended usage of JP7? Does it have something to do that Nucleo-G474RE comes with nSWBOOT0 option bit cleared?

Uwe Bonnes · ‎2019-07-26

Well, the jumper allows to pull PB8-BOOT0 low. It give you options to play with.

Mike_ST · ‎2019-07-26

Dear Yoichi,

Yes you are right, on this board, by default, the option bytes are set with nSWBOOT0=0 and nBOOT0=1.

Meaning that, in this case, pin BOOT0-PB8 is not used for BOOT configuration, and you can use PB8 as normal I/O.

You are free to set back nSWBOOT to 1 thanks to STM32CubeProgrammer and use PB8 for BOOT configuration.

Yoichi Shinoda · ‎2019-07-26

PB8-BOOT0 is active high when used as BOOT0; pulling it down doesn't have any effect in this case. For using PB8-BOOT0 as GPIO, why this particular pin is provisioned for pull down?

Yoichi Shinoda · ‎2019-07-26

Yes. I understand the nSWBOOT option. My question is about "an intended usage of JP7".

Yoichi Shinoda · ‎2019-07-26

Yes. I understand the nSWBOOT option. My question is about "an intended usage of JP7".

Mike_ST · ‎2019-07-26

When nSWBOOT=1, and JP7 is fitted, it allows to pull-down BOOT0/PB8, and avoid having BOOT0 floating.

When nSWBOOT=0 and JP7 not fitted, you can use PB8 on CN5 or CN7.

Yoichi Shinoda · ‎2019-07-26

Okay, so JP7 should be fitted to keep BOOT0 from floating in nSWBOOT = 1 mode.

This suggest G4's BOOT0 behavior is different from predecessors like F4, in which BOOT0 could be left floating at any time?