Methods and circuits provide function-appropriate signaling to multi-functional circuits on a constrained set of communication lines. A first communication line receives digital signals. The second communication line is employed for digital signaling related to a first function. In further steps, the method comprises initiating, based on a multi-value logic digital signal on the first communication line, an activation process that generates a second-function activation signal. Upon receipt of the second-function activation signal, the second communication line is employed for digital signaling related to a second function. Preferred activation processes involve monitoring the second communication line for a digital signature and sending the activation signal upon detection of an appropriate signature.