2 - Hardware Description [U3 Datasheet]
The U3 has 3 different I/O areas:
Communication Edge,
Screw Terminal Edge,
DB Edge.
The communication edge has a USB type B connector (with black cable connected in Figure 2-1). All power and communication is handled by the USB interface.
The screw terminal edge has convenient connections for the analog outputs and 8 flexible I/O (digital I/O, analog inputs, timers, or counters). The screw terminals are arranged in blocks of 4, with each block consisting of Vs, GND, and two I/O. There is also a status LED located on the left edge.
The DB Edge has a D-sub type connectors called DB15 which has the 8 EIO lines and 4 CIO lines. The EIO lines are flexible like the FIO lines, while the CIO are dedicated digital I/O.