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                    Multi-Processor Communication functions
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  This subsection provides a set of functions allowing to manage the USART 
  multiprocessor communication.
  
  For instance one of the USARTs can be the master, its TX output is connected to 
  the RX input of the other USART. The others are slaves, their respective TX outputs 
  are logically ANDed together and connected to the RX input of the master.

  USART multiprocessor communication is possible through the following procedure:
     1. Program the Baud rate, Word length = 9 bits, Stop bits, Parity, Mode transmitter 
        or Mode receiver and hardware flow control values using the USART_Init()
        function.
     2. Configures the USART address using the USART_SetAddress() function.
     3. Configures the wake up method (USART_WakeUp_IdleLine or USART_WakeUp_AddressMark)
        using USART_WakeUpConfig() function only for the slaves.
     4. Enable the USART using the USART_Cmd() function.
     5. Enter the USART slaves in mute mode using USART_ReceiverWakeUpCmd() function.

  The USART Slave exit from mute mode when receiving the wake up condition.