STM32L412C8 USART2 RX TX pin swap not working

[KAsim]

I am using the STM32L412C8 and I am having trouble with the USART2 RX/TX pin swapping. I enabled it in CubeMX but if I send data to the PA2 pin (originally TX but should be RX after the swap) I get nothing. If however I send my data to PA3(should be TX after the swap) data instantly comes in. Checking the CR2 register of the USART, the SWAP bit is set.

What am I doing wrong?

[Uwe Bonnes]

Did you configure PA2 as peripheral?

[KAsim]

Yes, and I tried both push-pull and open drain.

[S.Ma]

Both pins should be alternate function configured. Otherwise, check the errata sheet.

[KAsim]

Both have been configured for USART2. The errata sheet has nothing relevant.

[S.Ma]

I've got STM32L4R5 connected to HC-06 BT module with wires, will give it a try tomorrow to check it at my desk.

[S.Ma]

Well it works on stm32l4r5. However, UE can t apparently be reset manually in debug mode.

[KAsim]

Would you mind sharing your code or the ioc file from CubeMX?

[waclawek.jan]

OP's problem may also be the way how Rx is handled, regardless of the swap...

JW

[KAsim]

What do you mean? I have used both HAL and LL functions to receive data and the result was the same.

[waclawek.jan]

And what about a simple status-register-based polling loop?

You could also read out and post the content of the UART registers, and maybe also the relevant GPIO registers.

Have you observed the received waveform directly on the Rx pin, using oscilloscope or LA?

Can you disconnect the target device and loop back Tx to Rx?

JW

[KAsim]

So an update:

A simple polling of RDR shows nothing received.

The USART registers are: CR1: 0xd , CR2: 0x8000, CR3:0

GPIOA MODER:0x6aa8a6a8 (so PA2, PA3 are 0x2)

GPIOA AFRL2=0x7,AFRL3=0x7

[KAsim]

I will try it tommorow and I'll let you know.

I have connected a USB-to-Serial in parallel and I can read data correctly so the waveform seems to be OK.

I can't disconnect it as it's soldered on a PCB but I might be able to short the two pins together.

Thank you for your help either way.

[waclawek.jan]

Hi @KAsim​  ,

Have you solved this issue?

JW

[KAsim]

Due to changes in the project, the whole PCB was redesigned, eliminating the need for pin swapping.

I never did manage to actually track down the problem though.

[waclawek.jan]

Thanks anyway for the info.

JW