Occur weird characters when I use serial to communicate between my STM32F4 Discovery with my pc using PL2303

I'm using HAL library to transmit and receive characters:

uint8_t c;
  /* USER CODE END 2 */

  /* Infinite loop */
  /* USER CODE BEGIN WHILE */
  while (1)
  {
    /* USER CODE END WHILE */

    /* USER CODE BEGIN 3 */
        if(HAL_UART_Receive(&huart5, &c, 1, 100) == HAL_OK)
        {
            HAL_UART_Transmit(&huart5, &c, 1, 100);
        }
  }

And after I install and load the code to my Discovery board, I use Hercules to start communicate and this hapen when I send a word or a letter: Occur weird characters when communicate using PL2303

I have tried to find the solution but it didn't appear. I hope someone can help me to resolve this problem.

Thanks for helping me, Ilya. I solved this problem by setting the input frequency = 8MHz (I had set it up to 16Mhz so the serial can't read and send the data with the true frequency).

Location of the input frequency in my problem