/**
  **************************************************************************
  * @file     readme.txt
  * @version  v2.0.0
  * @date     2021-11-26
  * @brief    readme
  **************************************************************************
  */

  this demo is based on the at-start board, in this demo, provides a basic
  communication between usart2 and usart3 using interrupt capability. if received
  data right, the three leds will blink.

  set-up
  - connect usart2 tx pin (pa2) to usart3 rx pin (pb11)
  - connect usart2 rx pin (pa3) to usart3 tx pin (pb10)
