Chapter 4 Signal ConnectionsDAQCard E Series User Manual4-34 National Instruments CorporationThe ADC switches to hold mode within 60 ns of the selected edge. Thishold-mode delay time is a function of temperature and does not varyfrom one conversion to the next. Separate the CONVERT* pulses byat least one conversion period.The sample interval counter on the DAQCard normally generates theCONVERT* signal unless you select some external source. Thecounter is started by the STARTSCAN signal and continues to countdown and reload itself until the scan is finished. It then reloads itself inreadiness for the next STARTSCAN pulse.A/D conversions generated by either an internal or externalCONVERT* signal are inhibited unless they occur within a dataacquisition sequence. Scans occurring within a data acquisitionsequence may be gated by either the hardware (AIGATE) signal orsoftware command register gate.AIGATE SignalAny PFI pin can externally input the AIGATE signal, which is notavailable as an output on the I/O connector. The AIGATE signal canmask off scans in a data acquisition sequence. You can configure thePFI pin you select as the source for the AIGATE signal in either thelevel-detection or edge-detection mode. You can configure the polarityselection for the PFI pin for either active high or active low.In the level-detection mode if AIGATE is active, the STARTSCANsignal is masked off and no scans can occur. In the edge-detectionFigure 4-21. CONVERT* Output Signal Timingt wt w = 50-100 ns
