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Chapter 4 Digital Input/Output and PFI
Digital Output Timing Signals
The cDAQ chassis features the following DO timing signals:
• DO Sample Clock Signal*
• DO Sample Clock Timebase Signal
• DO Start Trigger Signal*
• DO Pause Trigger Signal*
Signals with an * support digital filtering. Refer to the PFI Filters section for more information.
DO Sample Clock Signal
The DO Sample Clock (do/SampleClock) signals when all the digital output channels in the task
update. DO Sample Clock can be generated from external or internal sources as shown in
Figure 4-4.
Figure 4-4. Digital Output Timing Options
Routing DO Sample Clock to an Output Terminal
You can route DO Sample Clock to any output PFI terminal. DO Sample Clock is active high
by default.
DO Sample Clock Timebase Signal
The DO Sample Clock Timebase (do/SampleClockTimebase) signal is divided down to provide
a source for DO Sample Clock. DO Sample Clock Timebase can be generated from external or
internal sources, and is not available as an output from the chassis.
DO Start Trigger Signal
Use the DO Start Trigger (do/StartTrigger) signal to initiate a waveform generation. If you do
not use triggers, you can begin a generation with a software command. If you are using an
internal sample clock, you can specify a delay from the start trigger to the first sample. For more
information, refer to the NI-DAQmx Help.
Programmable
Clock
Divider
DO Sample Clock
Timebase
PFI
Analog Comparison Event
Ctr n Internal Output
DO Sample Cloc
Analog Comparison
Event
20 MHz Timebase
80 MHz Timebase
PFI
100 kHz Timebase
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