Xon/Xoff Software Handshaking - National Instruments GPIB-232CV-A User Manual

Chapter 3 Operation of the GPIB-232CV-A

XON/XOFF Software Handshaking

GPIB-232CV-A User Manual
setup allows each device to monitor the RTS signal of the other device and
to suspend transmission when necessary to prevent data loss. Refer to
Appendix B, Interfacing to a Serial
schemes.
If your serial device does not implement or recognize the hardware
handshake scheme, your cable does not support the necessary handshake
lines, or your application software requires XON/XOFF handshaking, you
might need to enable the XON/XOFF handshaking protocol by setting
switch 8 of SW2 to ON. This handshaking protocol performs the same
function as the hardware handshake but does so by sending special control
codes over the data lines instead of changing logic levels on dedicated
control lines.
When you enable the XON/XOFF protocol, the GPIB-232CV-A sends the
XOFF character (decimal 19 or <Ctrl-S>) before the internal buffer
overflows. When the GPIB-232CV-A is able to start receiving characters
again, it sends the XON character (decimal 17 or <Ctrl-Q>). Similarly, if
the GPIB-232CV-A is transmitting data and receives the XOFF character,
it suspends transmission of any further data until it receives the XON
character.
If you are transmitting binary data, do not configure the GPIB-232CV-A
to use XON/XOFF software handshaking. Because the binary data could
contain any binary sequence, including decimal 19 (<Ctrl-S>) or
decimal 17 (<Ctrl-Q>), the GPIB-232CV-A would not be able to
distinguish between data values or handshake control codes. If
handshaking were enabled, the GPIB-232CV-A would handshake
erratically.
Device, for more information on wiring
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