Synchronizing unit for receiving section of PCM station

A synchronizing unit controlling the operation of a receiving station of a PCM station of a telecommunication system, comprising:

• timing means stepped by line-clock pulses extracted from an incoming bit stream organized into alternating first and second frames each containing a multiplicity of channels accommodating respective data words, an initial channel No. 0 of each first and second frame normally containing a respective alignment word A and B characterized by at least one invariable bit in a predetermined time position, and timing means generating clock signals fed to said receiving section and further emitting first and second marking pulses TA and TB in a time slot assigned to the No. 0 channel of said first and second frames, respectively;
• correlation means including a decoder receiving said incoming bit stream and emitting respective identification pulses AX and BX upon recognizing said alignment words A and B, said correlation means further including logic circuitry generating an error signal FAT upon noncoincidence of said marking pulses TA and TB with the respective identification pulses AX and BX, said logic circuitry feeding corrective signals into said timing means for readjusting same to re-establish coincidence between said marking pulses and the corresponding identification pulses;
• and
• a malfunction detector connected to said correlation means and to said timing means for receiving therefrom at least one of said identification pulses and the corresponding marking pulse, said detector including gating means for producing an alarm indication AW in the absence of coincidence therebetween.