Counter period was 65535 from the beginning.

Thank you, I will try it.

Apart is '_' to separate data from each send. SerialPrint(...) used to be SerialPrint(uint16_t Tx) but I changed to uint32 to print the ARR.

OK, I will try it. I am just confused about the relationship between this issue and ARR. In other word, after I can observe the registers, how can I solve the problem?

Thank you for answering the question. I am a beginner of STM32 so I know little about the registers. This is SerialPrint() function.void SerialPrint(uint32_t Tx){ if(Tx == 0){ TxMessages[0] = '0'; HAL_UART_Transmit(&huart1 ,(uint8_t*)&TxMessages...