Chapter4 ConnectingSignals
©NationalInstruments Corporation 4-29 NI6013/6014 User Manual
SISOURCE Signal
Any PFIpin can externally input the SISOU RCEsignal, w hich isnot
availableas an output on the I/O connector. The onboard scan interval (SI)
counteruses SISOURCE as a clockto time theg eneration of
the STARTSCAN signal. You must configure the PFI pin you select as
the source for SISOURCE in the level-detection mode. You can configure
the polarity selection for the PFI pin for either active high or active low.
Themaximum allowed frequency is 20 MHz, with a minimum pulse width
of 23 ns high or low.There is no minimum frequency limitation.
Eitherthe 20 MHz or 100 kHz internal timebase generates SISOURCE
unless you select some external source. Figure 4-21 showst het iming
requirementsfor the SISOURCE signal.
Figure4-21. SISOURCE Signal Timing
SCANCLK Signal
SCANCLKis an output-only signal that generates a pulse with theleading
edgeoccurring approximately 50 to 100 nsafter an A/D conversion begins.
Thepolarity of this output is software-selectable but is typically configured
so that a low-to-high leading edge can clock external AI multiplexers
indicating when the input signal has been sampled and can be removed.
This signal has a 400 to 500 ns pulse width and is software enabled.
tw=23 ns minimum
tp=50 ns minimum
tw
tw
tp