Chapter 3 Connector Information
NI USB-621x User Manual 3-2 ni.com
+5 V Power
The +5 V terminals on the I/O connector can be use as either an output or
an input. Both terminals are internally connected on the USB-621x.
+5 V Power as an Output
Because the USB-621x devices are bus powered, there is a 50 mA limit on
the total current that can be drawn from the +5 V terminals and the digital
outputs PFI <4..7> and PFI <12..15>/P1.<0..7>. The USB-621x monitors
the total current and will drop the voltage on all of the digital outputs and
the +5 V terminals if the 50 mA limit is exceeded.
AO GND — — Analog Output Ground—AO GND is the reference for
AO <0..1>. All three ground references—AI GND,
AO GND, and D GND—are connected on the device.
D GND — — Digital Ground—D GND supplies the reference for
PFI <0..15>/P0/P1 and +5 V. All three ground
references—AI GND, AO GND, and D GND—are
connected on the device.
+5 V D GND Input or
Output
+5 V Power—These terminals provide a +5 V power
source or can be used to externally power the PFI outputs.
PFI <0..3>,
PFI <8..11>/P0.<0..7>
D GND Input Programmable Function Interface or Static Digital
Input Channels 0 to 7—Each PFI terminal can be used
to supply an external source for AI, AO, or counter/timer
inputs.
You also can use these terminals as static digital input
lines.
PFI <4..7>,
PFI <12..15>/P1.<0..7>
D GND Output Programmable Function Interface or Static Digital
Output Channels 0 to 7—You can route many different
internal AI, AO, or counter/timer outputs to each PFI
terminal.
You also can use these terminals as static digital output
lines.
NC — — No connect—Do not connect signals to these terminals.
Table 3-1. I/O Connector Signals (Continued)
Signal Name Reference Direction Description
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