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Chapter 2 Function Reference — SCXI_Set_State
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National Instruments Corporation 2-363 NI-DAQ FRM for PC Compatibles
When channel = n, the LSB (bit 0) of data contains the state of channel n on the specified
port.
For relay modules, a 0 bit indicates that the relay is closed or in the normally closed position,
and a 1 indicates that the module is open or in the normally open position. For SCXI digital
modules, a 0 bit indicates that the line is low, and a 1 bit indicates that the line is high.
Note For a discussion of the NC and NO positions, see your SCXI module user manual.
Using This Function
Because the relays on the SCXI -1160 module have a finite lifetime, the driver will maintain
a software copy of the relay states as you write to them; this allows the driver to excite the
relays only when you specify a new relay state. If you call this function to specify the current
relay state again, NI-DAQ will not excite the relay again. When the SCXI-1160 powers up,
the relays remain in the same position as they were at power down. However, when you start
an application, the driver does not know the states of the relays; it will excite all of the relays
the first time you write to them and then remember the states for the remainder of the
application. When you call the
SCXI_Reset function, the driver will mark all relay states as
unknown.
The SCXI-1161 powers up with its relays in the NC position. The SCXI-1163 powers up with
its output lines high when you operate the module in multiplexed mode. The SCXI-1163R
powers up with relays open. If you operate the SCXI-1163 or 1163R in parallel mode, the
states of the output lines or relays are determined by the states of the corresponding lines on
the DAQ device.