In order to protect key parts of computer programs, the instructions making up those parts are held in an EPROM forming part of a single chip microcomputer. The EPROM is connected to instruction registers by way of an instruction bus. Data used by instructions held in these registers is transferred along...http://www.google.de/patents/US4823308?utm_source=gb-gplus-sharePatent US4823308 - Microcomputer with software protection
