System for modifying a logic controller instruction set

Abstract

A programmable logic controller includes a read/write memory for storing multi bit instructions which direct computations in the controller in response to a programming keyboard module connected to the controller for encoding instructions to be stored in controller memory. Keyboard commands transfer instructions from the module to said memory in an ordered array. Instructions are read from memory serially, cyclically and non destructively for operation of the controller. A keyboard insert command inserts a new instruction at a designated address in memory and sequentially shifts each serially accessed instruction in memory stored at an address beyond the designated address to a memory address once removed.