Abstract: A terminal of a digital telecommunication system working in a so-called "ping-pong" mode, with alternate reception and transmission of data words in respective halves of a recurrent operating cycle, has a phase-lock circuit whose oscillator is stabilized by a control signal periodically extracted from an incoming bit stream during the data-receiving phases. The receiving section of the terminal has a branch obtaining incoming bipolar data words from an input/output transformer and converting them, with the aid of a peak detector and an integrator or a monoflop, into respective timing pulses whose leading edges recur with the same periodicity as the data words.