| 摘要 |
PURPOSE:To improve the flexibility of the control, by setting preliminarily optionally whether branching between respective areas is valid or not in case that a privileged level is provided in different areas in a main storage. CONSTITUTION:An instruction 6 is read out by the address of an instruction address register 1; and if contents of a buffer register 7 are a branch instruction, addresses of the instruction address register 1 and a branch address part 9 are compared with each other. In this case, only upper N-number bits of the register 1 and the branch address part 9 are compared. If they coincide with each other, a branch in the same area is discriminated to execute the branch instruction of the buffer register 7. Otherwise, a branch to a different area is discriminated, and an entry for a branch destination area is read out from a branch control table 12 and is sent to a read branch validity check part 14. If this branch is valid, the branch instruction of the register 7 is executed; and if it is not valid, the execution of the instruction is suppressed. |
