Enabling LSE clock on PA8 from HEX code?

[DRich.4]

I am unable to communicate with the MCU via UART (115200 bit/s). It looks like the program inside MCU is not running. I think the problem can be probably in not running LSE 32.768kHz crystal oscillator.

Is it possible to enable LSE clock on PA8 if I have just the hex file to check it with oscilloscope? SWD via STLINK-V3MINI and STM32CubeProgrammer works great, I was able to upgrade the firmware with easy. I have S76G chip with STM32L07 inside.

[waclawek.jan]

IMO the PCB design is OK, capacitors sound roughly OK too.

If this is a prototype, double/triple check if you don't have shorts between pins/tracks. Try a different crystal - what if it got damaged during soldering and/or tests?

In the test program, make sure it does not time out and give up or switch to LSI too soon. Starting up a low-power crystal oscillator make last seconds or even tens of seconds.

Try the test program on a "known good" board such as Nucleo or Disco (or on the devboard you say is OK, if you are confident you can revert to the original firmware on it).

JW

PS. Cross-posted on a local forum.

[DRich.4]

When I changed the RCC_LSEDRIVE_LOW to HIGH it help to start the crystal by touching it by a finger, but the output frequency is 1/2 of 32.768KHz see picture:

 

I noticed that the crystal is soldered upside down i.e. Pin 1 input is going to OSC32_IN and Pin 2 output is going to OSC32_OUT. That may be the problem.

[DRich.4]

I have slightly modified the design for MEMS oscillator (SiT1533AI-H4-AA3-32.768E). Waiting for a new PCB to test it. Stay tuned ;-).