/**
  **************************************************************************
  * @file     readme.txt
  * @brief    readme
  **************************************************************************
  */
  
  this demo is based on the ht32f49395_sk board, in this demo,
  shows how to use usart to achieve rs485 communication.

  set-up
  - usart tx      --->   pa2
  - usart rx      --->   pa3
  - usart de      --->   pa1
