An integrateable circuit is disclosed which allows selection between pre-defined and user-defined characteristics. The circuit utilizes a single input terminal for both selection and definition by a user. In a preferred embodiment, a comparator senses whether a user-supplied voltage at this input terminal is at a logic low level or not. If the voltage at this input terminal is at a logic level low, an internal voltage proportional to a pre-defined characteristic is enabled. If the voltage at this input terminal is not at a logic low level, the internal voltage proportional to the pre-defined characteristic is disconnected and a characteristic defined by the user, its value proportional to the user-supplied voltage present at the input terminal, is connected and activated.