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Chapter 6 Digital I/O
DI Change Detection Applications
The DIO change detection circuitry can interrupt a user program when one of several DIO
signals changes state.
You also can use the output of the DIO change detection circuitry to trigger a DI or counter
acquisition on the logical OR of several digital signals. To trigger on a single digital signal, refer
to the Triggering with a Digital Source section of Chapter 11, Triggering. By routing the Change
Detection Event signal to a counter, you also can capture the relative time between samples.
You also can use the Change Detection Event signal to trigger DO or counter generations.
Connecting Digital I/O Signals
The DIO signals, P0.<0..31>, P1.<0..7>, and P2.<0..7> are referenced to D GND. You can
individually program each line as an input or output. Figure 6-4 shows P1.<0..3> configured for
digital input and P1.<4..7> configured for digital output. Digital input applications include
receiving TTL signals and sensing external device states, such as the state of the switch shown
in the figure. Digital output applications include sending TTL signals and driving external
devices, such as the LED shown in the figure.
Figure 6-4. Digital I/O Connections
Caution Exceeding the maximum input voltage ratings, which are listed in the
specifications document for each M Series device, can damage the DAQ device and
the computer. NI is not liable for any damage resulting from such signal connections.
+5 V
LED
TTL Signal
+5 V
Switch
I/O Connector
D GND
M Series Device
P1.<0..3>
P1.<4..7>
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