MEMORY CONTROL AND PROTECTION SYSTEM

PURPOSE:To execute write protection and execution protection for a user program in a program RAM with a simple hardware by discriminating whether memory access is valid or not by a mode signal, an operating status signal and and address signal. CONSTITUTION:When a processor unit 1 tries to execute the contents of the program RAM 6 in a non-execution mode of a user program, a chip selecting circuit 5 executes prescribed operation by using a processor operating status signal S1 indicating the execution of an processor instruction, an operation mode signal S3 indicating the non-execution mode of the user program and an address signal corresponding to a program RAM area and outputs an access abnormality interrupting signal S7 without outputting memory selecting signals S4-S6. Consequently, the execution is transferred to an interrupt program for interrupting the operation of a processor unit 1 and executing access abnormality processing to prevent the system for the generation of runaway.