A field-replaceable unit (FRU) identification circuit includes a reference voltage source, a reference resistor, a plurality of comparators, and a plurality of comparator input voltage sources. The reference voltage source provides a reference voltage. A first end of the reference resistor is electrically connected to the reference voltage source. Each comparator has two inputs and an output. A first input of each comparator is electrically connected to a second end of the reference resistor. The comparator input voltage sources each provide a comparator input voltage to the second input of one of the comparators. When an FRU is electrically connected to a circuit board where the FRU identification circuit is located, the outputs of the comparators are set to a distinct combination of logical values that uniquely identifies the FRU.