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Console Serial Lines, Communications, BREAK?

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The Question is:

Certain hardware devices (i.e GE Funac PLC) require the break duration of a
 specific length of time. The "Break" duration is significantly longer when the
 PLC is directly connected to the Alpha COM port in respect to a terminal
 server (Print server/90tl).
 Can the break duration be set via the operating system?

The Answer is :

  Please see the FAQ for a discussion of the BREAK signal and its
  underlying "implementation" -- you can generate a BREAK signal of
  your choice, simply by changing the speed of the serial line (to
  a speed that will cause framing errors) and generating characters
  on the line for the appropriate duration.
  BREAK signals and console lines are also discussed in the FAQ.
  Because of the nature of the console serial line, the OpenVMS
  Wizard would discourage its use for communications control of
  factory floor PLC devices.  (PLCs are notorious for odd serial
  line operations and protocols, use of control characters, and
  for single-character I/O.  Not all PLCs behave this way, but
  some do.  These attributes can cause OpenVMS to be halted on
  various systems, depending on the characters received, and
  the character processing required for some PLC protocols can
  be resource-intensive.  These attributes can tend to be
  incompatible with console operations and console assumptions.)
  For details on the OpenVMS terminal driver and its available
  function codes, please see the I/O User's Reference Manual.
  (The console serial line OPDRIVER driver does not entirely
  match the terminal driver -- again, the OpenVMS Wizard would
  not tend to use the console serial line for purposes other
  than as a console.)

answer written or last revised on ( 22-SEP-2002 )

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