Common control constant shift reframe circuit

Abstract

The disclosed reframe circuit utilizes common control circuitry to carry out a reframing operation for any, or all, of a plurality of time division multiplexed digital data groups which are out-of-frame. An old data store is used to store a given number (m) of selected data bits, of each digital group, for two frames for framing comparison purposes. A reframe comparator serves to compare, for each digital group, the m bit output of the old data store with m data bits that are two frames later in time. A suitability store is used to record, for each group, which of the compared m data bits have had framing pattern violations and which appears as a suitable candidate for the framing bit. Based on the present set of comparisons and past suitabilities, a shift decoder searches for the framing bit within the current m-bit window until it has either marked all m bits unsuitable or has found the true framing bit within the window. If all m bits are unsuitable, the data bits of an out-of-frame digital group are shifted m bit positions, m new bits are loaded into the old data store, the suitability store is initialized for these new m bits, and the described operation is repeated. When the shift decoder finds a bit that is suitable for a given number of consecutive frames and hence is the true framing bit, the digital group is placed in-frame by shifting the data bits thereof one to m bit positions.