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The designated space next to each USER <1..2> BNC is for marking or labeling signal names.
Connecting Digital I/O Signals
Use the DIO <0..20> connectors of the BNC-9920 to connect to channels DIO <0..20> of the NI 9403.
The DIO <0..7> connectors are screw terminals with indicator LEDs, DIO 8 is a BNC connector, and
DIO <9..20> are screw terminals without LED indicators. You can individually configure each signal in
LabVIEW as an input or output. Refer to the NI 9403 Operating Instructions and Specifications for
information about these lines. The BNC-9920 also has two screw terminals for the D GND and +5 V
lines.
The LEDs next to the screw terminals for DIO <0..7> indicate the state of each digital line, as shown in
Table 1.
Digital I/O LED
Using the Quadrature Encoder
The BNC-9920 contains a mechanical quadrature encoder circuit that produces 96 pulses per encoder
revolution. Two outputs, PULSES and UP/DN, are at the screw terminals located below the quadrature
encoder knob. To use the quadrature encoder with the NI 9403, connect the PULSES terminal and the
UP/DN terminal to any two DIO lines of the NI 9403.
PULSES outputs a pulse train generated by rotating the encoder shaft. It provides four pulses per one
mechanical click of the encoder. UP/DN outputs a high or a low signal indicating rotation direction.
When the direction is counterclockwise, UP/DN is low. When the direction is clockwise, UP/DN is high.
BNC-9920 Operating Instructions and Specifications
BNC Cable
DIO 16
Signal
Figure 6. Connecting PFI 8 to USER 1 BNC
Lit
The port is either pulled high or driven high
Not lit
The port is either pulled low or driven low
TIMING I/O
Screw Terminal Block
USER 1 BNC
D GND
Table 1. Digital I/O LEDs
Digital Port State
8
DIO 16
DIO 17
DIO 18
DIO 19
DIO 20
+5 V
D GND
Wire
Internal
Connection
USER 1
ni.com
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