Abstract: An encoding transmitting unit converts parallel data words into timing pulse synchronized serial data words which are supplied to a transmission channel, and a decoding receiving unit receives the transmitted serial data words from the transmission channel. The encoding unit comprises a clock-pulse generator and a control circuit connected to a shift register receiving the parallel data words and having a feedback, through an inverter, from a serial word output to an additional input which is a serial word input for the inverted output signal. The shift register transmits a first pulse train representing the serial data word followed by a second pulse train representing the inverted serial data word. The decoding receiving unit includes a second shift register having a serial data word input receiving the two pulse trains from the transmission channel and having a serial data word output.