Multi-Program Patch for Read-Only Memories
Original Publication Date: 1980-Jan-01
Included in the Prior Art Database: 2005-Feb-13
Many programmable machines having program (PGM) execution circuits are controlled by read-only memories (ROMs) such as shown in program store C. Once the machines are installed, it becomes very expensive to change the machine each time a function is added or corrections have to be made to the program store. It is much easier to perform what is commonly referred to as "patching" the ROM. Usually this is achieved by monitoring the instruction word address and when a certain address appears, the program execution circuits receive the instruction word from a patch store B rather than from a program store.