STM32H5 JTDO/TRACESWO pin not working as UART7_RX despite alternate function support

[Jinal]

Hi ST community,

I’m working with an STM32H563 MCU and trying to use the pin labeled JTDO/TRACESWO as UART7_RX because the datasheet/alternate function table shows that this pin supports UART7_RX.

However, UART transmission works correctly, but UART reception does not work when using this pin. If I switch to a different pin, both TX and RX function as expected.

Here’s what I’ve checked so far:

• Configured the pin in STM32CubeMX as UART7_RX (alternate function mode)
• Verified UART7 peripheral initialization is correct
• Checked baud rate and UART settings
• Confirmed hardware wiring:
  • External TX connected to STM32 UART7_RX
  • Common GND connected
  • Signal level is 3.3V
• Tried disabling trace/SWO in CubeMX by setting by debug to “Serial Wire” instead of trace mode
• Also tested with debugger disconnected after programming

My question:

• Is the JTDO/TRACESWO pin fully usable as UART7_RX on STM32H5, or is it reserved/limited due to debug trace functionality?
• Is there any additional register/configuration needed to release this pin from SWO/JTAG?
• Has anyone successfully used this pin as UART RX in an STM32H5 project?

MCU part number: STM32H563RGT6
Package: LQFP64
Pin name: PB7/UART7_RX(55 num Pin)
Toolchain: STM32CubeMX / STM32CubeIDE
Debugger: ST-Link V2

Any guidance would be appreciated. Thanks!

[mƎALLEm · Accepted solution]

Hello,

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@Jinal wrote:

Pin name: PB7/UART7_RX(55 num Pin)

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You mean PB3 not PB7.

Ok but did you disconnect the debugger probe while testing the UART? This pin is used also by the Serial Wire Debug: SWO signal.