| 摘要 |
PROBLEM TO BE SOLVED: To surely prevent an undesirable access by inhibiting access to a part of a program situation work register, all registers that are used in a system mode and a memory based on mode bit value of the register. SOLUTION: When a control line 27 is connected to a prescribed part of a program situation word register 28 including a mode bit, the bit value decides whether a microprocessor operates in a system mode or in a user mode. When the bit value shows the system mode, a connection unit 30 is driven through a single bus that mutually connects two bus parts 21 and 23 and registers 18, 24, 26 and 28 and all special function registers are mutually connected. Also, when it shows the user mode, the unit 30 is driven through the line 27 and the two bus parts 21 and 23 are separated from each other. In such a case, an access is not available any more between the registers 18, 28 and 24 and the other registers. |
