Using Programmable Controllers for Sequential Systems with Random Inputs

A new method is presented for programming programmable controllers for random-input systems, in which the various input signals do not appear in any predefined order. The method is somewhat related to the well-known Huffman method for designing asynchronous sequential systems. However, while Huffman's method is limited to small problems, the method suggested here can be used with any number of input variables. Also, it is much easier to apply than Huffman's method, and does not involve filling in of Karnaugh maps. While the suggested method does not minimize the number of required relays, this does not represent a drawback where the solution is implemented with programmable controllers, since the number of relays available in even small programmable controllers is generally more than required.