NI USB-9421 User Guide and Specifications
12
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Figure 7.
Pin Assignments
Connecting Devices to the NI USB-9421
The NI USB-9421 has
sinking inputs
, meaning that when current goes
through or voltage is applied to the DI terminal or pin, DI provides a path
to ground for the current or voltage. The NI USB-9421 internally limits
current signals connected to DI. For more information about input current
protection, refer to the
section.
You can connect 2-, 3-, and 4-wire
sourcing-output
devices to the
NI USB-9421. A sourcing-output device drives current or applies voltage
to DI. An example of a sourcing-output device is a PNP open collector.
Connect the output of the sourcing-output device to DI on the
NI USB-9421. Connect the common of the external device to the COM
terminal or pin. Figure 8 shows a possible configuration.
COM
NC
COM
COM
NC
COM
COM
NC
COM
COM
NC
COM
COM
DI0
NC
DI1
DI2
NC
DI
3
DI4
NC
DI5
DI6
NC
DI7
1
2
3
4
5
6
7
8
9
10
11
12
1
3
14
15
16
17
1
8
19
20
21
22
2
3
24
25
0
3
4
7