STM32F429I-DISCO - USART3 outputs only 1.6V

[smrtkai]

Hi everyone,

I am trying to get USART3 running on my STM32F429I-DISCO board. USART3 is configured with the following configurations:

• Mode: Asynchronous
• Hardware Flow Control: Disable
• Baudrate: 115200, Word Length: 8, Stop Bits: 1
• GPIO: PD8 = TX, PD9 = RX

I have tried a lot of different configurations. In every configuration I have tried so far, PD8 outputs only a 1.6V signal. The receiver expects a 3.3V signal.

What might cause the "low" voltage at PD8?

Kind regards,

Kai

[waclawek.jan]

High load from external circuitry, bad solder joint.

Make sure the onboard SDRAM does not drive its data lines.

JW

[Tesla DeLorean]

Manual says the pin is used by the SDRAM, so two things driving in different states.

https://www.st.com/content/ccc/resource/technical/document/user_manual/6b/25/05/23/a9/45/4d/6a/DM00093903.pdf/files/DM00093903.pdf/jcr:content/translations/en.DM00093903.pdf

[smrtkai]

Thank you!!!

I am not using the SDRAM and it is not initialized. I have generated the code with STM32CubeMX only with the USART configuration.

How can I get it working with 3.3V?

[Tesla DeLorean]

You might not be using it, but you're still dragging the boat anchor.

Desolder the unused SDRAM, or lift the specific pin.