Modified Twisted-Ring Counter Circuit

In a twisted-ring counter (a feedback shift register in which the next input digit is the complement of the outgoing digit) with three or more stages, the state diagram consists of the desired sequence and other closed sequences composed of unused states. If the counter enters one of the latter, it will not enter the desired sequence. This correspondence points out the minimum modification necessary to ensure that, whatever state the counter is in initially, it will always, in due course, enter the desired sequence. It is shown that the input stage must not be reset unless a group of stages at the opposite end, m in number, are in the 1 state, where m is the smallest integer greater than n/3 and n is the number of stages.