The simplest multi-bit DAC is the Kelvin divider or String DAC. An N-bit version of this DAC simply consists of 2N  equal resistors in series and 2N switches, one between each node of the chain and the output. The output is taken from the appropriate tap by closing just one of the switches. A string DAC intended for use as a general purpose DAC has a resistor between the reference terminal and the first switch. For use as a digital potentiometer, all 0s and 1s should connect the variable tap to one or the other end of the string of resistors.