A variable resistor under the control of a digital signal is the digital potentiometer. Unlike traditional potentiometers, which employ mechanical motions, digital potentiometers use digital signals. Most often, a resistive ladder—a set of connected resistors in series—is used to do this. A protocol like I2C or SPI, as well as up and down signals, are used to regulate this digital resistor. Integrated circuits called digital potentiometers are available with volatile memory and non-volatile memory. A mixed signal device is the digital potentiometer. Three terminal potentiometer components make up the device's analogue portion. The registers, interface, and controls that work with the potentiometer make up the digital portion of the device.