National Instruments NI 9411 Operating Instructions And Specifications page 12

Connecting Single-Ended Devices to the NI 9411
You can connect single-ended (TTL) devices to the NI 9411.
Connect the signal to the DIa pin, but do not connect a signal to the
DIb pin in the pair. You must leave the second signal in the set of
signals unconnected. For example, if you connect a single-ended
signal to the pin for DI0a, leave DI0b unconnected. Figure 4 shows
a possible configuration.
Single-Ended
Device
Figure 4. Connecting a Single-Ended Device to the NI 9411
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External
Power Supply
+ –
V COM
sup
+5 V +5 V
out
Reg
DIa
out
Receiver
DIb
Circuitry
COM
NI 9411
11 NI 9411 Operating Instructions and Specifications