Chapter 3
Signal Connections
© National Instruments Corporation
3-9
DAQCard-500 User Manual
To measure frequency, program counter 2 to be level gated and count the number of falling
edges in a signal applied to the CLK2 input. The gate signal you applied to the GATE2 input is
of a known duration. In this case, program counter 2 to count falling edges at the CLK2 input
while the gate is applied. The frequency of the input signal then equals the count value divided
by the gate period. Figure 3-6 shows the connections for a frequency measurement application.
You could also use counter 1 to generate the gate signal in this application.
100 k
Ω
1 MHz
Gate
Source
DGND
Counter 2
OUT
CLK
GATE
+5 V
20
27
I/O Connector
DAQCard-500
26
24
25
Figure 3-6. Frequency Measurement Application
The CLK and OUT signals for counter 1 are available at the I/O connector. The GATE, CLK,
and OUT signals for counter 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 resistor.
Figure 3-7 shows the timing requirements for the GATE and CLK input signals and the timing
specifications for the OUT output signals of the MSM82C54.
