Abstract: A three level signal is converted to a two level signal for transmission through a bi-level digital device by separating the opposite polarity parts of the three level signal. One part is inverted at an inverter and devices such as monostables are used to form two pulse trains in which the pulse lengths are different. The pulse trains are combined at a mixer and then transmitted through the device. Also disclosed is a decoder for decoding the pulses after transmission through the device.

Abstract: An aligner with a time switching capability is disclosed. The aligner has a store for storing incoming data. The store is sufficiently large that it can hold more than one frame of information. Data is written into the store under the control of clock signals associated with the incoming data. Data is read from the store under the control of a local clock. Read addresses are generated by a unit which is so arranged that if a clash between the current write address and the generated read address is sensed to be imminent, reading of the corresponding address in the previous or subsequent frame occurs. Thus, the aligner can operate as a time switch and clashes between reading and writing are avoided by allowing slippage of one frame.