Circuits for detecting framing bits in a t.d.m. bit stream

Abstract

A framing circuit is disclosed for detecting framing bits in a t.d.m. bit stream having an extended DS1 framing format. The circuit comprises a RAM for storing in respect of each of the 772 time channels the five most recent information bits of the time channel and three other, candidate, bits which represent the likelihood that the particular time channel carries the framing bit pattern. The current and five stored information bits of each time channel are checked to detect the six-bit framing bit pattern. The candidate bits have their value increased or decreased, within predetermined limits, in dependence upon whether or not a phase of the framing bit pattern is detected, and the updated information and candidate bits are stored in the RAM. The modification of the candidate bits in this manner is effected in only every third 772-bit frame. A framing signal is produced in dependence upon the candidate bits.

Dependencies are inferred from the claim text.