COM_SOFT()
 Queries or sets the software handshake (automatic XON/XOFF)

 Syntax

     COM_SOFT(<nComPort>,[<lNewHandshake>],[<cXONchar>],
        [<cXOFFchar>]) --> lOldHandshake

 Arguments

     <nComPort>  Designates the port (1 to N) for which the software
     handshake is set.

     <lNewHandshake>  Designates whether the handshake is on (.T.) or off
     (.F.).  If this parameter is omitted, the function returns the current
     setting.

     <cXONchar>  Designates any character you choose as an XON character.
     The default character is ASCII 19 - Ctrl-S.

     <cXOFFchar>  Designates any character you choose as an XOFF
     character.  The default value is ASCII 17 - Ctrl-Q.

 Returns

     The function returns the previously set value.

 Description

     With modem connections, a hardware handshake is impossible, which is why
     we are making a software handshake available with this function.  When a
     buffer is 75% full, an XOFF character (Ctrl-Q) is transmitted to the
     remote station.  As soon as the buffer has again been emptied to 50% or
     less, the XON character (Ctrl-S) is transmitted.  You can use characters
     other than Ctrl-S or Ctrl-Q for individual protocols, which would then
     be taken into account in the situations described above.

 Notes

     ”  The software handshake only supports background transmission
        (when COM_OPEN() has been implemented with the third parameter
        <nBufferOut>).

     ”  When you want to transmit binary data, the software handshake
        must always be turned off.

 Example

     COM_OPEN(1, 1000, 1000)   // Open port, background transmission
     COM_SOFT(1, .T.)          // Software handshake COM1