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                               Smartcard mode functions
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  This subsection provides a set of functions allowing to manage the USART 
  Smartcard communication.
  
  The Smartcard interface is designed to support asynchronous protocol Smartcards as
  defined in the ISO 7816-3 standard.

  The USART can provide a clock to the smartcard through the SCLK output.
  In smartcard mode, SCLK is not associated to the communication but is simply derived 
  from the internal peripheral input clock through a 5-bit prescaler.

  Smartcard communication is possible through the following procedure:
     1. Configures the Smartcard Prsecaler using the USART_SetPrescaler() function.
     2. Configures the Smartcard Guard Time using the USART_SetGuardTime() function.
     3. Program the USART clock using the USART_ClockInit() function as following:
        - USART Clock enabled
        - USART CPOL Low
        - USART CPHA on first edge
        - USART Last Bit Clock Enabled
     4. Program the Smartcard interface using the USART_Init() function as following:
        - Word Length = 9 Bits
        - 1.5 Stop Bit
        - Even parity
        - BaudRate = 12096 baud
        - Hardware flow control disabled (RTS and CTS signals)
        - Tx and Rx enabled
     5. Optionally you can enable the parity error interrupt using the USART_ITConfig()
        function
     6. Enable the USART using the USART_Cmd() function.
     7. Enable the Smartcard NACK using the USART_SmartCardNACKCmd() function.
     8. Enable the Smartcard interface using the USART_SmartCardCmd() function.

  Please refer to the ISO 7816-3 specification for more details.

Note: 
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  1.  It is also possible to choose 0.5 stop bit for receiving but it is recommended 
      to use 1.5 stop bits for both transmitting and receiving to avoid switching 
      between the two configurations.
  2. In smartcard mode, the following bits must be kept cleared:
     - HDSEL and IREN bits in the USART_CR5 register.