1. A method of specifying a transmitter, the transmitter for regulating an amplitude of a supplied current to encode a parameter, the method comprising providing a set of data to a customer, wherein the set of data represents a maximum allowable load at one or more supply voltage levels, and the set of data has a first segment operable only for a lower range of currents below a transition current and has a second segment operable only for a higher range of currents above the transition current.