Programmable controller unit and method of processing user program

摘要

A unit such as an I/O unit for a programmable controller stores a user program in a RAM but at least a portion of this user program is made into a library. At least a portion and maybe the whole of this user program is made into library and stored in a flash memory. The program thus made into a library can be executed when necessary but the flash memory is made in accessible by the tool and the program stored therein is protected from unauthorized person trying to read its content.