Improving Characteristics of LUT-Based Moore FSMs

Almost any digital system includes sequential blocks which can be represented using a model of finite state machine (FSM). It is very important to improve such characteristics of FSM circuits as the number of logic elements, operating frequency and consumed energy. The paper proposes a novel design method targeting a decrease in the number of look-up table (LUT) elements in logic circuits of FPGA-based Moore FSMs. The method is based on using two sets of variables for encoding the collections of outputs. It results in a partition of the set of outputs by two blocks. The outputs from the first block depend on state variables, the outputs from the second block on additional variables. A method is proposed for splitting the set of outputs. The conditions for using the proposed method are given. An example of synthesis is shown. The results of experiments with standard benchmarks are discussed. The experiments outcomes show that the proposed approach allows diminishing the number of LUTs and consumed energy. Also, it leads to an increase in the operating frequency. The method targets rather complex FSMs when the number of state variables exceeds the number of LUT's inputs.