Abstract: The synchronous serial communication circuit transmits and receives data, which is added flag patterns for recognizing the coil winding direction at the first and last of data block, by the electromagnetic induction system using a pair of coils. So, the circuit provides modulation and demodulation circuits acting at the clock of twice of the transfer speed and a flag check circuit for recognizing the inversion of the coil winding direction by judging a state of the flag patterns included in the received data. The transmitted data is converted into the biphase signal by the modulation circuit and is transmitted by driving the coil using the biphase signal. The signal received by the coil is converted into the received data by the demodulation circuit. When the winding directions of coils does not agree, the flag check circuit recognizes the inversion of the coil winding direction and the received data is inverted by the demodulation circuit.

Abstract: A low power line driving transmission apparatus is described in which TDM signals are transmitted between points over a transmission line comprising a pair of conductors and in which the characteristic impedance of the tranmission line and the source impedance of the transmitters is matched and wherein the input impedance of the receivers is sufficiently high to present an effective open circuit to received signals. Under these conditions the transmitter dissipates power only during logical transitions of the input signals.

Abstract: The system comprises at least one teleprinter station (1) connected to an exchange (3) by means of a transmission-reception line (2) and comprising a polarity detector (31) for the line circulating current, and a device (30) for reversing the connection of the line wires. If the wires erroneously become reversely connected following maintenance work on a line of single current type, then false call and conversation signals are generated which automatically trigger a checking operation in which the polarity detector is suitably examined under control of a ROM routine E controlling a CPU 84. If the current is found to be the reverse of the correct current, the reversing device is operated in order to reverse the polarity of the connection. In contrast, in the case of a double current line, the reversing device is operated when current is absent in the reception line, thus indicating an erroneous line connection. If the line current interruption is prolonged, a warning device (28) is activated.