National Instruments E Series User Manual

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National Instruments E Series User Manual Manual pdf 65 page image

Chapter 4 Signal ConnectionsNational Instruments Corporation4-29DAQCard E Series User ManualTRIG2 SignalAny PFI pin can externally input the TRIG2 signal, which is availableas an output on the PFI1/TRIG2 pin.Refer to Figure 4-11 for the relationship of TRIG2 to the dataacquisition sequence.As an input, the TRIG2 signal is configured in the edge-detectionmode. You can select any PFI pin as the source for TRIG2 andconfigure the polarity selection for either rising or falling edge. Theselected edge of the TRIG2 signal initiates the posttriggered phase of apretriggered acquisition sequence. In pretriggered mode, the TRIG1signal initiates the data acquisition. The scan counter indicates theminimum number of scans before TRIG2 can be recognized. After thescan counter decrements to zero, it is loaded with the number ofposttrigger scans to acquire while the acquisition continues. TheDAQCard ignores the TRIG2 signal if it is asserted prior to the scancounter decrementing to zero. After the selected edge of TRIG2 isreceived, the DAQCard acquires a fixed number of scans and theacquisition stops. This mode acquires data both before and afterreceiving TRIG2.As an output, the TRIG2 signal reflects the posttrigger in apretriggered acquisition sequence. This is true even if the acquisitionis being externally triggered by another PFI. The TRIG2 signal is notused in posttriggered data acquisition. The output is an active highpulse with a pulse width of 50 to 100 ns. This signal is set to input(High-Z) at startup.This document was created with FrameMaker 4.0.4