Halfduplex mode function
[USART_Private_Functions]

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                   ##### Half-duplex mode function #####
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    [..] This subsection provides a set of functions allowing to manage the USART
         Half-duplex communication.
    [..] The USART can be configured to follow a single-wire half-duplex protocol 
         where the TX and RX lines are internally connected.
    [..] USART Half duplex communication is possible through the following procedure:
         (#) Program the Baud rate, Word length, Stop bits, Parity, Mode transmitter 
             or Mode receiver and hardware flow control values using the USART_Init()
            function.
         (#) Configures the USART address using the USART_SetAddress() function.
         (#) Enable the half duplex mode using USART_HalfDuplexCmd() function.
         (#) Enable the USART using the USART_Cmd() function.
         [..]
         (@) The RX pin is no longer used.
         (@) In Half-duplex mode the following bits must be kept cleared:
             (+@) LINEN and CLKEN bits in the USART_CR2 register.
             (+@) SCEN and IREN bits in the USART_CR3 register.