Chapter 8 PFI© National Instruments Corporation 8-5 NI 6238/6239 User ManualThe filter setting for each input can be configured independently. On powerup, the filters are disabled. Figure 8-4 shows an example of a low-to-hightransition on an input that has its filter set to 125 ns (N = 5).Figure 8-4. Filter ExampleEnabling filters introduces jitter on the input signal. For the 125 ns and6.425 μs filter settings, the jitter is up to 25 ns. On the 2.55 ms setting, thejitter is up to 10.025 μs.When a PFI input is routed directly to RTSI, or a RTSI input is routeddirectly to PFI, the M Series device does not use the filtered version of theinput signal.Refer to the KnowledgeBase document, Digital Filtering with M Seriesand CompactDAQ, for more information about digital filters and counters.To access this KnowledgeBase, go to ni.com/info and enter the infocode rddfms.I/O ProtectionEach DI, DO, and PFI signal is protected against overvoltage andundervoltage conditions as well as ESD events on NI 6238/6239 devices.Table 8-1. FiltersFilter SettingN (FilterClocks Neededto Pass Signal)Pulse WidthGuaranteed toPass FilterPulse WidthGuaranteed toNot Pass Filter125 ns 5 125 ns 100 ns6.425 μs 257 6.425 μs 6.400 μs2.55 ms ~101,800 2.55 ms 2.54 msDisabled — — —1 2 31 4 1 2 3 4 5RTSI, PFI, orPXI_STAR TerminalFilter Clock(40 MHz)Filtered InputFiltered input goes highwhen terminal is sampledhigh on five consecutivefilter clocks.
