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Chapter 2 Function Reference — SCXI_Track_Hold_Setup
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National Instruments Corporation 2-371 NI-DAQ FRM for PC Compatibles
receive the source signal from the SCXIbus and drive the scan interval timer of the DAQ
device, if you want; or the module can use the DAQ device counter output and send the signal
on the SCXIbus, even if that module is not in the module scan list.
For example, you want to scan two SCXI-1140 modules; one of which is cabled to the DAQ
device that is to perform the acquisition. An external signal connected to the HOLDTRIG pin
of the module that is not cabled to the DAQ device is to control the track/hold state of both
modules and the scan interval during the acquisition. The
SCXI_Track_Hold_Setup
parameters would be as follows:
• For the SCXI-1140 that is cabled to the DAQ device:
inputMode = 2
source = 2
send = 1
• For the other SCXI-1140 module to be scanned:
inputMode = 2
source = 1
send = 2
Remember to call the
DAQ_Config function to enable external scan interval timing whenever
the source signal of a module will be driving the scan interval counter, as in the previous
example.
The module will go back into track mode after n module scan list entries for that module have
occurred, where n is the holdCount. Usually, each module is represented in the module scan
list only once, so a holdCount of one is appropriate. However, if an SCXI-1140 module is
represented more than once in the module scan list and you want the module to remain in hold
mode until after the last scan list entry for that module, you will need to set the module
holdCount to equal the number of times the module is represented in the module scan list.