Figure 6-2. digital waveform triggering – National Instruments Network Device DAQ S User Manual
Page 62
Chapter 6
Digital I/O
© National Instruments Corporation
6-3
Digital Waveform Triggering for Non-Isolated Devices
(NI 6124 Only)
NI 6124 devices do not have an independent DI or DO Start
Trigger for digital waveform acquisition or generation. To trigger a DI or
DO operation, first select a signal to be the source of DI Sample Clock or
DO Sample Clock. Then, generate a trigger that initiates pulses on the
source signal. The method for generating this trigger depends on which
signal is the source of DI Sample Clock or DO Sample Clock.
For example, consider the case where you are using AI Sample Clock as the
source of DI Sample Clock. To initiate pulses on AI Sample Clock (and
therefore on DI Sample Clock), you use AI Start Trigger to trigger the start
of an AI operation. The AI Start Trigger causes the non-isolated
DAQ-STC2 S Series device to begin generating AI Sample clock pulses,
which in turn generates DI Sample clock pulses, as shown in Figure 6-2.
Figure 6-2. Digital Waveform Triggering
Similarly, if you are using AO Sample Clock as the source of DI Sample
Clock, then AO Start Trigger initiates both AO and DI operations.
If you are using a Counter output as the source of DI Sample Clock, the
counter’s start trigger, enables the counter which drives DI Sample Clock.
If you are using an external signal (such as PFI x) as the source for
DI Sample Clock or DO Sample Clock, you must trigger that external
signal.
Digital Waveform Acquisition for Non-Isolated Devices
(NI 6124 Only)
You can acquire digital waveforms on the Port 0 DIO lines.
The DI waveform acquisition FIFO stores the digital samples. S Series
devices have a DMA controller dedicated to moving data from the
DI waveform acquisition FIFO to system memory. The DAQ device
samples the DIO lines on each rising or falling edge of a clock signal,
DI Sample Clock.
PFI 1
(AI Start Trigger)
AI Sample Clock
DI Sample Clock
AI Start Trigger initiates
AI Sample Clock and DI Sample Clock.