STM32WL55JC1 – HSE clock not starting

[Sjain]

Hi ST team, 

I am working on STM32WL55JC1. I am trying to enable the HSE external crystal oscillator, but it never starts.

In firmware, I configure RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSE; and set HSEState = RCC_HSE_ON. After enabling, I confirmed that HSEON set, however HSERDY flag in RCC->CR never becomes set.

I have tried:

• Both Crystal/Ceramic Resonator mode and Bypass mode in CubeMX. In Bypass mode with external clock it works but in Crystal mode failed.
• Using HAL_RCC_OscConfig() followed by HAL_RCC_ClockConfig().
• Forcing HSE output on MCO pin (PA8) → no signal observed.

Hardware Verification Done:

• External 32 MHz crystal (NX2016SA-32M-EXS00A) with correct load capacitors (as per datasheet).
• Verified soldering, power rails, and grounding.
• Crystal reference design followed exactly (same as ST Nucleo-WL55 board).
• Supply voltage and decoupling capacitors confirmed OK.

Attempts Made:

• Full chip erase + reflash minimal firmware that just enables HSE and outputs it on MCO.
• Checked BOOT0 and reset conditions.
• Verified RCC_CR shows HSEON = 1 but HSERDY = 0.
• Tried lowering load capacitance and even replacing the crystal.
• Tested on two separate boards with identical result.

Could you please confirm:

1. If there are any known issues with HSE startup on STM32WL55JC1 devices?
2. If additional configuration (debug auth, option bytes, special modes) is required to enable HSE?
3. it would be really helpful if you provide any reference example to enable HSE clock, I tried LoRa end-node example, clock configuration using STM32cubeMx.
   

Thanks,
Shivangi

[STTwo-32]

Hello @Sjain 

There is not a known issue on the HSE for the STM32WL series. It may be an issue on your HW design, and you have to check it with a HW expert maybe. Also, you can use the RCC_ClockConfig example that switch between HSI and HSE using the B1 on the NUCLEO-WL55JC1 to check that the SW is not the source of the issue for your case.

Best Regards.

STTwo-32