Simple flexible indexing method for ros storage microcomputers

Abstract From the Canadian patent

An improved method of modifying fixed instructions in a read only memory in a data processing system is described. The instructions stored in the read only memory are made modifiable by data stored in a random access memory. In operation, an instruction is retrieved from the read only memory and data is retrieved from the random access memory in accordance with a previously retrieved instruction. When the last retrieved instruction is to be modified an indexing gate enables the data from the random access memory to be combined with the last retrieved instruction in an adder or like logic device. The output of the adder or like logic device is the modified instruction. This simple …