NI cDAQ-9178 - Page 58

NI cDAQ-9178/9174 User Guide and Specifications 58 ni.com
Figure 54 shows the output waveform of the frequency generator when the divider is set to 5.
Figure 54. Frequency Generator Output Waveform
Frequency Output can be routed out to any PFI terminal. All PFI terminals are set to high-impedance at
startup. The FREQ OUT signal also can be routed to many internal timing signals.
In software, program the frequency generator as you would program one of the counters for pulse train
generation.
For information about connecting counter signals, refer to the Default Counter/Timer Routing section.
Frequency Division
The counters can generate a signal with a frequency that is a fraction of an input signal. This function is
equivalent to continuous pulse train generation. Refer to the Continuous Pulse Train Generation section
for detailed information.
For information about connecting counter signals, refer to the Default Counter/Timer Routing section.
Pulse Generation for ETS
In the equivalent time sampling (ETS) application, the counter produces a pulse on the output a specified
delay after an active edge on Gate. After each active edge on Gate, the counter cumulatively increments
the delay between the Gate and the pulse on the output by a specified amount. Thus, the delay between
the Gate and the pulse produced successively increases.
The increase in the delay value can be between 0 and 255. For instance, if you specify the increment to
be 10, the delay between the active Gate edge and the pulse on the output increases by 10 every time a
new pulse is generated.
Suppose you program your counter to generate pulses with a delay of 100 and pulse width of 200 each
time it receives a trigger. Furthermore, suppose you specify the delay increment to be 10. On the
first trigger, your pulse delay will be 100, on the second it will be 110, on the third it will be 120; the
process will repeat in this manner until the counter is disarmed. The counter ignores any Gate edge that
is received while the pulse triggered by the previous Gate edge is in progress.
The waveform thus produced at the counter’s output can be used to provide timing for undersampling
applications where a digitizing system can sample repetitive waveforms that are higher in frequency
than the Nyquist frequency of the system. Figure 55 shows an example of pulse generation for ETS; the
delay from the trigger to the pulse increases after each subsequent Gate active edge.
Frequency
Output
Timebase
FREQ OUT
(Divisor = 5)