Chapter 4 Signal Connections
DAQCard E Series User Manual
4-40
National Instruments Corporation
Figure 4-27 shows the timing requirements for the GPCTR1_SOURCE
signal.
The maximum allowed frequency is 20 MHz, with a minimum pulse
width of 23 ns high or low. There is no minimum frequency limitation.
The 20 MHz or 100 kHz timebase normally generates the
GPCTR1_SOURCE unless you select some external source.
GPCTR1_GATE Signal
Any PFI pin can externally input the GPCTR1_GATE signal, which is
available as an output on the PFI4/GPCTR1_GATE pin.
As an input, the GPCTR1_GATE signal is configured in
edge-detection mode. You can select any PFI pin as the source for
GPCTR1_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 such actions as starting and stopping the
counter, generating interrupts, saving the counter contents, and so on.
As an output, the GPCTR1_GATE signal monitors the actual gate
signal connected to general-purpose counter 1. 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 4-27.
GPCTR1_SOURCE Signal Timing
t
p
t
w
t
w
t
p
t
w
= 50 ns minimum
= 23 ns minimum
