/**
  **************************************************************************
  * @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 description
  of how to use the usart in smartcard mode. the example gives only the possibility
  to read the atr and decode it into predefined buffer.if test pass, the three leds
  will turn on.
  - sc usart tx      --->   pa2
  - sc usart clk     --->   pa4
  - sc usart 3_5v    --->   pa5
  - sc usart reset   --->   pa6
  - sc usart cmdvcc  --->   pa7
  - sc usart off     --->   pa8
