Chapter 3
Connector and LED Information
3-3
ni.com
+5 V Power
The +5 V terminals on the I/O connector can be
u
se as either an o
u
tp
u
t or
an inp
u
t. Both terminals are internally connected on the USB-621
x
.
+5 V Power as an Output
Beca
u
se the USB-621
x
devices are b
u
s powered, there is a 50 mA limit on
the
total
c
u
rrent that can be drawn from the +5 V terminals and the digital
o
u
tp
u
ts. The USB-621
x
monitors the total c
u
rrent and drops the voltage
on all of the digital o
u
tp
u
ts and the +5 V terminals if the 50 mA limit is
exceeded.
+5 V Power as an Input
If yo
u
have high c
u
rrent loads for the digital o
u
tp
u
ts to drive, yo
u
can
exceed the 50 mA internal limit by connecting an ex5 V power
so
u
rce to the +5 V terminals. These terminals are protected against
u
ndervoltage and overvoltage, and they have a f
u
se to protect them from
short circ
u
it conditions
1
. If yo
u
r USB-621
x
device has more than one +5 V
terminal, yo
u
can connect the external power s
u
pply to one terminal and
u
se the other as a power so
u
rce.
USER
—
—
(USB-621
x
BNC Devices)
User-Defined Channel
—The USER
BNC connector allows yo
u
to
u
se a BNC connector for a digital
or timing I/O signal of yo
u
r choice. The USER BNC connector
is internally ro
u
ted to the USER screw terminal. Refer to the
appropriate
USER
section for yo
u
r USB-621
x
BNC device in
Appendix A,
, for more
information abo
u
t the USER signal.
NC
—
—
No connect
—Do not connect signals to these terminals.
*
USB-6212/6216 BNC/Mass Termination devices have eight digital I/O lines, P0.<0..7>.
1
USB-621
x
Screw Terminal/BNC devices have a 350 mA self-resetting f
u
se. USB-621
x
Mass Termination devices have a
750 mA
u
ser-replaceable socketed f
u
se. Refer to the
section for information abo
u
t replacing
socketed f
u
ses.
Table 3-1.
I/O Connector Signals (Continued)
Signal Name
Reference
Direction
Description
