nucleo_g474: mysterious bytes received on UART Rx

[pasuzw]

Hi Guys

I am doing a project and I notice that if I unplug the UART cable(FTDI) and then connect it again, there is a chance that there would be mysterious bytes received from RDR.

What is more interesting is that the mysterious bytes are actually the messages that was sent out to UART Tx.

During the testing, I am not using any UART serial monitoring tool like Putty or what's so ever, so there should not be any inputs to the UART Rx.  But it just happened, not often, but if I repeat disconnect and reconnect dozens of times, then something from UART Tx got into the UART Rx buffer.

I have confirmed that those mysterious bytes are read out from RDR.

Has any one know what's happening ? 

Thanks.

[TDK]

Is RX floating? If so, nearby pins will influence it, such as TX.

If it's not floating, then there is probably another explanation. Code bug, misinterpretation, etc.

[pasuzw]

Blue is Rx and Yello is Tx.   There seems no pull up on Rx, so it drops when UART cable is disconnected.