Abstract: A line interface circuit (12.sub.1) having a digital interface (18) and an analog interface (20) coupled to the digital interface by a transmission path (23, 26) may be tested by launching a digital value into the digital interface while the analog interface is terminated by termination impedance (35). The digital value launched into the line interface circuit is converted to an analog signal within the circuit which appears across the termination impedance, creating a voltage that is sensed back on the transmission path. This sensed voltage is convened within line interface circuit back to a digital value for output at the digital interface in response to the originally launched digital test value.

Abstract: Disclosed are methods of controlling the adjustment of a machine-adjustable component in a circuit wherein a feedback factor relates a change in a monitor parameter to a compensating change in the value of the adjustable component; and wherein, by machine means, a value for the change in the monitor parameter is determined, a target value for the adjustable component is calculated from the monitor parameter change and the feedback factor, and the adjustable component is adjusted to substantially its target value.