Dynapro Technologies Dynapro ET TCS, Руководство разработчика приложений

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The XON/XOFF Mode command sets or resets the TCS XON/XOFF Mode. On the Setup
Screen, the user can select one of the following parameters:
•
on
•
off
The XON/XOFF Mode determines whether the TCS uses XON and XOFF codes for
communication flow control. Regardless of the XON/XOFF Mode setting, the TCS always uses
the SRTS and CTS control lines for flow control, if they are connected to the host.
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While the XON/XOFF Mode is set (on), the TCS automatically sends an XOFF or XON code
when it needs to stall or unstall the host. The TCS treats XON and XOFF codes specially while
operating in this mode. When sending these codes to the host, the TCS assigns priority and
transmits them immediately, ahead of any other codes that may be in the output buffer.
When the user types Ctrl/S or Ctrl/Q on the optional keyboard, the TCS handles these keystrokes
as commands to stall or unstall the host. The TCS sends an XOFF or XON immediately to the
host and exercises the SRTS control line.
When an XON or XOFF is received from the host, the TCS always processes it immediately,
even if the input buffer is full.
While XON/XOFF Mode is reset (off), the TCS does not automatically send XOFF or XON
codes to stall or unstall the host. XON and XOFF codes can be sent while this mode is reset, but
only when the user types Ctrl/Q or Ctrl/S respectively on the optional keyboard. In this case, the
XON and XOFF codes, are not assigned priority and are handled like any other codes in the
output buffer.
The TCS handles the Ctrl/S and Ctrl/Q keystrokes as though they were not intended to stall and
unstall the host. The TCS sends the keystrokes in the order they are typed and does not exercise
the SRTS control line. When an XON or XOFF is received from the host, the TCS ignores it.
The code is not treated as a communication control code, and it cannot be received when the TCS
input buffer is full.
The only time XON/XOFF Mode should be reset is when flow control is either not needed, or is
handled exclusively by control lines.
For further information on flow control, see Buffer Overflow Control, in Chapter 2.