Chapter 4 Signal ConnectionsNational Instruments Corporation4-39VXI-MIO Series User ManualFigure 4-29 shows the timing requirements for the GPCTR0_SOURCEsignal.Figure 4-29. GPCTR0_SOURCE Signal TimingThe maximum allowed frequency is 20 MHz, with a minimum pulsewidth of 23 ns high or low. There is no minimum frequency limitation.The 20 MHz or 100 kHz timebase normally generates theGPCTR0_SOURCE signal unless you select some external source.GPCTR0_GATE SignalAny PFI pin can externally input the GPCTR0_GATE signal, which isavailable as an output on the PFI9/GPCTR0_GATE pin.As an input, the GPCTR0_GATE signal is configured in theedge-detection mode. You can select any PFI pin as the source forGPCTR0_GATE and configure the polarity selection for either rising orfalling edge. You can use the gate signal in a variety of differentapplications to perform actions such as starting and stopping thecounter, generating interrupts, saving the counter contents, and so on.As an output, the GPCTR0_GATE signal reflects the actual gate signalconnected to general-purpose counter 0. This is true even if the gate isbeing externally generated by another PFI. This signal is set to input(High-Z) at startup.Figure 4-30 shows the timing requirements for the GPCTR0_GATEsignal.t pt w t wt pt w= 50 ns minimum= 23 ns minimum
