Abstract: A circuit for detecting and verifying a presence of a terminating device for a high speed data transmission line. The circuit contains a first cable detector which generates a first signal if a first cable is present. A second cable detector generates a second signal if a second cable is present. The terminating device is contained in a plurality of resistor packs, each of the which contains an extra resistor. A terminating device detector senses the extra resistor presence, thereby detecting the presence of the resistor packs. The terminating device detector generates an ALL-EQUIPPED signal and a NON-EQUIPPED signal, the ALL-EQUIPPED signal is generated when all of the plurality of resistor packs are present, the NON-EQUIPPED signal is generated when all of the plurality of resistor packs are absent. Finally, a verifier circuit receives the first signal, the second signal, the ALL-EQUIPPED signal and the NON-EQUIPPED signal.

Abstract: A transmission arrangement includes a switched resonant circuit (5) for switching data states of digital signals on a pair of transmission lines (1, 2) and a regenerative circuit (7) for feeding power back on the lines. The switched resonant circuit has a switching device (22) connected in series with an inductance (20) and parallel with a capacitance (21). A digital logic system (8) controls the switching device such that switching occurs at a line current zero crossover point. Where a change of data state is to be transmitted to a receiver (6), the logic system (8) turns the switching device on at an appropriate time. The switching device is switched off when the voltage (+Vm) on the lines reaches approximately the same magnitude in the opposite sense (-Vm). The change in the line voltage indicates a change of the data state to the receiver.