A digital-unit interface comprises a first node, a second node, a third node, and an amplifier assembly. The first node is connected to a pull-up resistor and is configured to be connected to the signal line of a transmission line connected to a first digital unit at a distal point. The second node is configured to be connected to a second reference electrical potential, a signal-return line of the transmission line, and a signal-return line of a second digital unit. The third node is configured to be connected to a signal line of the second digital unit. The amplifier assembly is configured to be connected between the first node and the third node and to transform between high electrical potentials on the first node and lower electrical potentials on the third node while the second digital unit communicates with the first digital unit.