The application of threshold logic to the design of sequential machines

The application of threshold logic to the design of sequential machines is the subject of this paper. A single layer of threshold logic units in the combinational portion of a sequential machine is used as the general model to be studied, and investigations have been made in the areas of autonomous machines, counters, sequence generators, and general input-output machines. This model was chosen for study because it offers the combined advantages of fewer components because of the use of threshold logic, along with very high-speed operation resulting from the use of only a single layer of logic. In some instances, namely for asynchronous machines, the only delay need be the natural delay of the single layer of threshold elements. Two state-assignment procedures are given for the synthesis of counters, both based on manipulations of C-matrices. The first results in counters having the minimum number of state variables; the second in race-free counters for which only one state variable changes per change of state. The modification of a given code to make it realizable with the chosen network is discussed and applied to the problem of outputs and sequence generators. Machines having inputs are considered and shown to present special problems; some of the difficulties involved are isolated. It is demonstrated that sometimes it is necessary to expand the state diagram by a state-splitting technique before the machine is realizable with the threshold network.