Systems for making impedance adjustments that will auto-tune a communication path is disclosed. The method can utilize time domain reflectometry (TDR) to acquire data about impedance mismatches and can adjust the termination impedances based on the acquired data. A system is also disclosed that has an isolator to decouple a first adjustable resistor from a transmission path in a first mode and couple the first adjustable resistor to the path in a second mode. The system can have a test transmitter to create a first current on the path in the first mode and to create a second current having twice the current in a second mode, wherein a detector can detect a first voltage during the first mode and a second voltage in the second mode as the first adjustable resistive load is adjusted in the second mode until it reaches a value matching the first voltage detected in the first mode.