NAME
       Stop -- pause all current I/O over the serial port

   FUNCTION
       This command halts all current I/O on the serial port by
       sending an xOFF to the "other side", and submitting a "logical
       xOFF" to "our side", if/when appropriate to current activity.

   IO REQUEST
       io_Message      mn_ReplyPort initialized
       io_Device       set by opendevice
       io_Unit         set by opendevice
       io_Command      CMD_STOP

   RESULTS

   SEE ALSO
       serial.device/cmd_start