National Instruments NI 2590/2591 - Manual (Page 22)

Chapter 2 NI 2590/2591 Operation
NI 2590/2591 User Manual 2-8 ni.com
Modes
SCANADV has two modes of operation. In its default mode, the
SCANADV trigger asserts for 1 µs after the relay has debounced. You
can also configure the switch module for handshaking mode, in which the
SCANADV trigger goes high after a relay settles, and the SCANADV
trigger goes low after the external trigger input asserts. You can use this
handshaking mode for multiboard scanning.
Note The NI 2590/2591 ignores external triggers when it is not in a wait-for-trigger state
while scanning.
Initiating Scanning
When you use the NI 2590/2591 to initiate a scan, make sure the
measurement device is armed (waiting for trigger) before enabling
scanning on the switch module. Enabling scanning causes the first
switch(es) in the scan list to close and generates a scanner advanced
trigger after the relay switches have settled or debounced.
When you use the measurement device to initiate a scan, make sure
scanning is enabled on the NI 2590/2591 before the measurement device
starts to take measurements. This ensures that the switch module has the
correct signal routed and that the switch module is waiting for an external
trigger from the measurement device.
Always configure the triggers in a system before configuring the
measurement device or the NI 2590/2591 for scanning. When triggers
are configured, a state change or pulse could occur on the trigger line.
This is also possible when you reset the switch module.
Multiboard Triggering
You can use multiple NI 2590/2591 switch modules—or multiple other
National Instruments switch modules such as the NI 2503—together in
conjunction with an instrument such as a National Instruments
oscilloscope/digitizer. In multiple switch-module systems, be sure to
identify one switch module as the master switch module.
All other switch modules for the system are identified as slave switch
modules. The master switch module can route an external trigger from the
front connector to a PXI backplane trigger. In addition, the master switch
module can route the SCANADV trigger from the PXI backplane to either
the front connector or another backplane trigger. This functionality makes