National Instruments E Series - Manual (Page 74)

Chapter 4 Signal Connections
DAQCard E Series User Manual 4-38  National Instruments Corporation
The 20 MHz or 100 kHz timebase normally generates the
GPCTR0_SOURCE signal unless you select some external source.
GPCTR0_GATE Signal
Any PFI pin can externally input the GPCTR0_GATE signal, which is
available as an output on the PFI9/GPCTR0_GATE pin.
As an input, the GPCTR0_GATE signal is configured in the
edge-detection mode. You can select any PFI pin as the source for
GPCTR0_GATE and configure the polarity selection for either rising
or falling edge. You can use the gate signal in a variety of different
applications to perform actions such as starting and stopping the
counter, generating interrupts, saving the counter contents, and so on.
As an output, the GPCTR0_GATE signal reflects the actual gate signal
connected to general-purpose counter 0. This is true even if the gate is
being externally generated by another PFI. This signal is set to input
(High-Z) at startup.
Figure 4-25 shows the timing requirements for the GPCTR0_GATE
signal.
GPCTR0_OUT Signal
This signal is available only as an output on the GPCTR0_OUT pin.
The GPCTR0_OUT signal reflects the terminal count (TC) of
general-purpose counter 0. You have two software-selectable output
options—pulse on TC and toggle output polarity on TC. The output
polarity is software selectable for both options. This signal is set to
Figure 4-25. GPCTR0_GATE Signal Timing in Edge-Detection Mode
Rising-edge
polarity
Falling-edge
polarity
t
w
t
w
= 10 ns minimum