Transmitting section of PCM station

A transmitting section of a PCM station of a telecommunication system, comprising:

• channel-forming means for organizing n-bit data words into alternating first and second outgoing frames each containing a multiplicity of channels accommodating respective data words, said channel-forming means including an input register with n stages accommodating respective bits of an arriving data word loaded into same, an output register with n stages, and a multiplexer with n outputs connected to respective stage inputs of said output register and with a plurality of inputs connected to respective stage outputs of said input register, said multiplexer having additional inputs connected to points of fixed potential representing predetermined logical values;
• timing means stepped by a local clock for identifying an initial channel No. 0 of each frame and controlling said multiplexer to replace certain bits of a data word in the No. 0 channel of each frame by predetermined bits yielding partly invariable alignment words A and B loaded into said output register in said first and second frames, respectively, said timing means emitting a frame-designating signal switching part of the outputs of said multiplexer to certain of said additional inputs thereof during the No. 0 channel of said second frames while leaving other multiplexer outputs connected to the associated stage outputs;
• decoding means emitting supervisory instructions upon detecting certain bit groupings in a data word loaded into said input register in the No. 0 channel of a frame;
• and
• switching means connected to said decoding means for generating internal signals in response to said supervisory instructions, said multiplexer being further controlled by said switching means for modifying a bit in one of said alignment words in the presence of said supervisory instructions.