BRR of STM32F401RCT6 changed when hot swapping

[Pzhu.1]

When the USART is  hot swapping，some datas will occur on TX RX pin；and the value of BRR register will be changed;the picture 1 shows the BRR before  hot swapping;and the picture 2 shows the BRR after  hot swapping.

Why this question happens?And what can I do to avoid this quetion?​

[TDK]

> When the USART is hot swapping

What do you mean by this? What is being hot swapped?

Pictures don't come through if you just paste them. You need to upload them with the "Image" icon tool.

[Pzhu.1]

this is picture1this is picture 2

The USART of STM32 is connected to another terminal with a network cable;when plugging the cable,some Interference  datas like"FF"will occur on the RX pin of STM32 ;then the value of BRR will be change 。