STM32F446 using UART4 to interface NEO M9N GPS not working

FShah.1 · ‎2025-06-18

Hi,

I am trying to interface the SparkFun Neo M9N GPS module with an STM32F446 MCU using UART4, but I am unable to receive any GPS data. Interestingly, when I switch to USART1, the module works perfectly.

Could you please help me understand why UART4 is not functioning while USART1 works fine? Additionally, I could not find any reference code for interfacing the module using I2C. If any source or example is available, it would be greatly appreciated.

Thank you!

mƎALLEm · ‎2025-06-25

Hello,

Hard to tell what the problem is based on the information you provided.

What board are you using? may be also you need to share your code/project.

Make sure you set the same configuration for UART4 as for USART1. Make sure you have used the correct Tx/Rx pins for UART4.

To give better visibility on the answered topics, please click on "Accept as Solution" on the reply which solved your issue or answered your question.

Andrew Neil · ‎2025-06-25

As @mƎALLEm said, you need to provide more detail - see: How to write your question to maximize your chances to find a solution.

Have you tested with a terminal that you can receive anything on UART4?

Have you confirmed that GPS data is actually reaching the UART4 Rx pin?

Some tips on debugging serial comms:

https://community.st.com/t5/community-guidelines/how-to-write-your-question-to-maximize-your-chances-to-find-a/ta-p/575228#:~:text=tips%20specifically%20on%20Debugging%20Serial%20Comms%3A

A complex system that works is invariably found to have evolved from a simple system that worked.
A complex system designed from scratch never works and cannot be patched up to make it work.