Microcomputer having a protection function in a register

A microcomputer including a processor for executing instructions, and comprising:

• a control unit for controlling execution of the instruction according to results of decoding of instruction codes;
• a first bus;
• a second bus;
• a general-purpose register file coupled between the first bus and the second bus and including a plurality of general-purpose registers;
• an operation unit coupled between the first bus and the second bus and configured to receive data to be processed from the general-purpose register file and to output an operation result to the general-purpose register file;
• an access attribute storage unit for storing an access attribute for each of said plurality of general-purpose registers;
• a mode storage unit for storing a mode for controlling an operation of said processor;
• and
• an access determining unit for determining, when a request for access to a general-purpose register of the plurality of general-purpose registers is made by said control unit, whether access to the general-purpose register is to be allowed or not, depending on the access attribute stored in said access attribute storage unit and the mode stored in said mode storage unit
• wherein when an exception request occurs, the access attribute stored in said access attribute storage unit is saved in another storage area, and the mode stored in said mode storage unit is changed.