Communication systems for receiving and checking repeatedly transmitted multi-digital telegrams

Claim 1

In a communication system in which information is conveyed in digital code in the form of a repeatedly transmitted multidigital telegram, checking equipment through which the successive telegrams are passed sequentially at a receiving station, said checking equipment comprising a plurality of serially connected shift registers each having a number of stages with respective outputs corresponding to the number of information bits of the digital telegram so that each stage of one said shift register and the corresponding stage of another said shift register produce outputs related to the corresponding information bits of sequentially transmitted multidigital telegrams, and a plurality of logic circuit elements equal in number to the number of stages in each of said shift registers, each of said logic circuit elements having inputs connected to each of the corresponding outputs of the shift registers, said logic circuit elements including means responsive to a disparity between corresponding outputs from said plural shift registers respectively to prevent passing of the corresponding information bit of the track telegram beyond the checking equipment.