© National Instruments | 3-5
X Series User Manual
+5 V Power Source
The +5 V terminals on the I/O connector supply +5 V referenced to D GND. Use these terminals 
to power external circuitry.
Caution Never connect the +5 V power terminals to analog or digital ground or to 
any other voltage source on the X Series device or any other device. Doing so can 
damage the device and the computer. NI is not liable for damage resulting from such 
a connection.
The power rating on most devices is +4.75 VDC to +5.25 VDC at 1 A.
Refer to the device specifications to obtain the device power rating.
Note (PCI Express X Series Devices) Some PCI Express X Series devices 
supply less than 1 A of +5 V power unless you use the disk drive power connector. 
Refer to the 
PCI Express Device Disk Drive Power Connector section for more 
information.
USER 1 and USER 2
The USER 1 and USER 2 BNC connectors allow you to use a BNC connector for a digital or 
timing I/O signal of your choice. The USER 1 and USER 2 BNC connectors are routed internally 
to the USER 1 and USER 2 screw terminals, as shown in Figure 3-1.
Figure 3-1.  USER 1 and USER 2 BNC Connections
USER 2 BNC
D GND
AI SENSE
AI GND
+5 V
D GND
USER 2
USER 1
CHS GND
AI SENSE 2
APFI 0
Internal
Connection
USER 1 BNC
D GND
Screw
Terminal
Block