A digital potentiometer is a digitally controlled resistor that changes the impedance between the terminals and the wiper depending on the code loaded in the RDAC register. Digital potentiometers avoid the problems that mechanical potentiometers face, such as physical size and wear and tear, as well as sensitivity to vibration, temperature, and humidity. A digital potentiometer can be configured in two different modes: potentiometer mode and rheostat mode.
Potentiometer mode (see Figure 1) has three terminals: Terminal A, Terminal B, and Terminal W (wiper).
Figure 1. Potentiometer Mode.
Rheostat mode has Terminal W hardwired to either Terminal A or Terminal B (see Figure 2). Some devices offer only two terminals: Terminal A and Terminal W.
Figure 2. Rheostat Mode.