An anesthetic agent cassette is provided for selectively communicating with an anesthesia machine using either analog or digital communication techniques. The anesthetic agent cassette includes an input contact that receives an input signal from an anesthesia machine. Based upon the input signal, the control circuit in the anesthetic agent cassette determines whether the anesthetic agent cassette is coupled to an anesthesia machine that utilizes either digital communication or analog communication. The anesthetic agent cassette includes an output circuit that selectively connects either a digital output line or an analog output line to a single output contact.