National Instruments 700 - Manual (Page 35)

Signal Connections Chapter 3
DAQCard-700 User Manual 3-16 © National Instruments Corporation
To measure time lapse, program a counter to be edge gated. Apply an edge to the counter GATE
input to start the counter. Program the counter to start counting after receiving a low-to-high
edge. The time lapse since receiving the edge equals the counter value difference (loaded value
minus the read value) multiplied by the CLK period.
To measure frequency, program a counter to be level gated and count the number of falling edges
in a signal applied to a CLK input. The gate signal you applied to the counter GATE input is of
a known duration. In this case, program the counter to count falling edges at the CLK input
while the gate is applied. The frequency of the input signal then equals the count value divided
by the gate period. Figure 3-9 shows the connections for a frequency measurement application.
You could also use a second counter to generate the gate signal in this application.
Signal
Source
13 DGND
Counter
OUT
CLK
GATE
+5 V
I/O Connector
DAQCard-700
Gate
Source
100 k Ω
Figure 3-9. Frequency Measurement Application
The GATE, CLK, and OUT signals for counters 1 and 2 are available at the I/O connector. In
addition, the GATE and CLK pins are pulled up to +5 V through a 100 k
Ω
resistor.
Figure 3-10 shows the timing requirements for the GATE and CLK input signals and the timing
specifications for the OUT output signals of the MSM82C54.