Chapter 4 Signal ConnectionsNational Instruments Corporation4-25VXI-MIO Series User Manualdriver for the PFI2/CONVERT* pin. Be careful not to drive a PFI signalexternally when it is configured as an output.As an input, you can individually configure each PFI for edge or leveldetection and also for polarity selection. You can use the polarityselection for any of the 13 timing signals, but the edge or level detectionwill depend upon the particular timing signal being controlled. Thedetection requirements for each timing signal are listed in the sectionthat discusses that individual signal.In edge-detection mode, a minimum pulse width of 10 ns is required.This applies for both rising-edge and falling-edge polarity settings.There is no maximum pulse-width requirement in edge-detection mode.In level-detection mode, there are no minimum or maximumpulse-width requirements imposed by the PFIs themselves, but limitsmay be imposed by the particular timing signal being controlled. Theserequirements are listed later in this chapter.Data Acquisition Timing ConnectionsThe data acquisition timing signals are SCANCLK, EXTSTROBE*,TRIG1, TRIG2, STARTSCAN, CONVERT*, AIGATE, andSISOURCE.Posttriggered data acquisition allows you to view only data that isacquired after a trigger event is received. A typical posttriggered dataacquisition sequence is shown in Figure 4-11. Pretriggered dataacquisition allows you to view data that is acquired before the trigger ofinterest in addition to data acquired after the trigger. Figure 4-12 showsa typical pretriggered data acquisition sequence. The description foreach signal shown in these figures is included later in this chapter.Figure 4-11. Typical Posttriggered Acquisition13 04 2TRIG1STARTSCANCONVERT*Scan Counter
