NAME
       write -- send output to serial port

   FUNCTION
       This command causes a stream of characters to be written out
       the serial port. The number of characters is specified in
       io_Length, unless -1 is used, in which case output is sent until
       a null(0x00) is encountered.

   IO REQUEST
       io_Message      must have mn_ReplyPort initialized
       io_Device       set by opendevice
       io_Unit         set by opendevice
       io_Command      CMD_WRITE
       io_Flags        Set IOF_QUICK to try quick I/O
       io_Length       number of characters to transmit, or if set
                       to -1 transmit until null encountered in buffer
       io_Data         pointer to block of data to transmit

   RESULTS
       Error -- if the write succeded, then io_error will be null.
           If the write failed, then the io_error will be non-zero.

   SEE ALSO
        serial.device/sdcmd_setparams