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Flashing fails on STM32WL5MOC6HTR when PB8 is set high (STSAFE power pin on “S” variant)

shreyaschandran
Associate II

Hello ST team,

We are using the STM32WL5MOC6HTR module, which does not include the STSAFE-A110 secure element.

However, in the STM32WL5MOC6HS variant, the PB8 pin is used to power the STSAFE chip (VDD_STSAFE).

In our setup (with the HTR module), when we set PB8 high during testing, the flashing process (using ST-Link / STM32CubeProgrammer) fails or hangs.

When PB8 is left floating or configured as input, flashing works normally.

I want to understand:

Why does driving PB8 high prevent flashing on the STM32WL5MOC6HTR module?

Is PB8 internally connected or reserved for STSAFE even on the non-S variant?

Should PB8 be kept floating or pulled low when STSAFE is not populated?

Any hardware or reference design explanation would be very helpful.

Thank you!

Module: STM32WL5MOC6HTR

Observed Behavior: Flashing fails when PB8 is driven high.

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