Abstract: A microprocessor based system for both creating and emulating control read only memories (CROM) for use in conjunction with programmable calculators and the like. The development system operates as two independent yet integrated systems. The system generates programmable calculator key codes from source code entered via a system computer keyboard, then maps the code into the system's read/write random access memory in the proper CROM format, and generates a gate placement tape from data stored in that memory. Additionally, the system emulates a CROM for real time interconnection to the programmable calculator. Thus, actual in calculator testing of the generated key codes is made possible prior to commitment of the code to mask and permanent manufactured CROMS.