National Instruments Eight-slot USB Chassis NI cDAQ-9172 - Manual (Page 62)

NI cDAQ-9172 User Guide and Specifications 62 ni.com
Frequency Generation
You can generate a frequency by using a counter in pulse train generation
mode or by using the frequency generator circuit.
Using the Frequency Generator
The frequency generator can output a square wave at many different
frequencies. The frequency generator is independent of the two
general-purpose 32-bit counter/timer modules on the NI cDAQ-9172
chassis.
Figure 39 shows a block diagram of the frequency generator.
Figure 39. Frequency Generator Block Diagram
The frequency generator generates the Frequency Output signal. The
Frequency Output signal is the Frequency Output Timebase divided by a
number you select from 1 to 16. The Frequency Output Timebase can be
either the 20 MHz Timebase divided by 2 or the 100 kHz Timebase.
The duty cycle of Frequency Output is 50% if the divider is either one or an
even number. For an odd divider, suppose the divider is set to D. In this
case, Frequency Output is low for (D + 1)/2 cycles and high for (D – 1)/2
cycles of the Frequency Output Timebase.
Figure 40 shows the output waveform of the frequency generator when the
divider is set to 5.
Figure 40. Frequency Generator Output Waveform
100 kHz Timebase
20 MHz Timebase
Frequency
Output
Timebase
Freq Out
Divisor
(1–16)
Frequency Generator
÷
2
Frequency
Output
Timebase
FREQ OUT
(Divisor = 5)