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 Opens and initializes a communications channel for input or output (I/O);
 must be executed before a device can be used for communication using an
 RS232 interface.
 
    OPEN "COMn: optlist" [FOR mode] AS [#]filenum% [LEN = reclen%]
 
    ■ n            Communications port to open:
                   • 1 = COM1
                   • 2 = COM2
 
    ■ optlist      Optional communication parameters; the most frequently
                   used options are:
 
                       [speed] [,[parity] [,[data] [,[stop]]]]
 
      Option    Description                      Range (Default in Bold)
      ═══════   ══════════════════════════════   ═══════════════════════════
      speed     Baud rate (bits per second)      75, 110, 150, 300, 600,
                                                 1200, 1800, 2400, 9600
      parity    Method of parity checking        N, E, O, S, M, PE
                (none, even, odd, space, mark,
                error checking)
      data      Number of data bits per byte     5, 6, 7, or 8
      stop      Number of stop bits              1, 1.5, or 2(*)
      ──────────────────────────────────────────────────────────────────────
      (*) The default value is 1 for baud rates > 110. For baud rates <= 110,
          the default value is 1.5 when data is 5; otherwise, the value is 2.
 
    ■ mode         Keyword specifying mode:
                   • OUTPUT            Sequential output mode
                   • INPUT             Sequential input mode
                   • RANDOM (default)  Random-access mode
 
    ■ filenum%     Any unused file number between 1 and 255, inclusive
 
    ■ reclen%      Size of a random-access-mode buffer; default is 128 bytes
 
 See Also
    ◄OPEN Statement (File I/O)►        ◄Opening a COM port►