OPTIMAL ENCODING OF CONTROL LOGIC.

Abstract

A new technique for encoding PLA-based control units is presented. Control units, specified at the functional level by tables of mnemonic strings, are encoded into a Boolean representation that minimizes the size of the control-store implemented by a PLA. The proposed method is based on symbolic minimization of the combinational component of the control unit and on two related constrained ecoding problems. Symbolic minimization yields a minimal sum-of-product representation of the next-state transition functions, independently of the encoding of the primary inputs and control states. The first encoding problem is to find the minimum-length encoding among those that minimize the number of product terms of a PLA implementation. The second is to find a bounded-length encoding that minimizes the number of product-terms of a PLA implementation. Minimal-area PLA implementations of the control store can be found by trading off the solution to these problems. Two heuristic algorithms for solving the above problems are presented. Both have been implemented in a computer program.