National Instruments PCI-6281, Руководство пользователя

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6-2
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Chapter 6 Digital I/O
The voltage input and output levels and the current drive levels of the DIO lines are listed in the
specifications of your device.
Static DIO
Each of the M Series DIO lines can be used as a static DI or DO line. You can use static DIO
lines to monitor or control digital signals. Each DIO can be individually configured as a digital
input (DI) or digital output (DO).
All samples of static DI lines and updates of DO lines are software-timed.
P0.6 and P0.7 on 68-pin M Series devices also can control the up/down input of general-purpose
counters 0 and 1, respectively. However, it is recommended that you use PFI signals to control
the up/down input of the counters. The up/down control signals, Counter 0 Up_Down and
Counter 1 Up_Down, are input-only and do not affect the operation of the DIO lines.
Digital Waveform Triggering
M Series 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 M 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.
PFI 1
(AI S t a rt Trigger)
AI Sa mple Clock
DI Sa mple Clock
AI S t a rt Trigger initi a te s
AI Sa mple Clock a nd DI Sa mple Clock.