| 摘要 |
PURPOSE:To switch as OS even by a CPU having no paging mechanism, by providing means for saving all registers of a processor, restoring them, and changing an effective address of the processor for executing an access to an execution address space, etc. CONSTITUTION:The first OS 8 saves a register, and thereafter, sets in advance a base address 10 of the second OS 9 as a data 1 of a CPU, to an OS switching register 3 by an OS switching instruction signal 2. In this way, the CPU generates an effective address by a timing for fetching an instruction being in the next address, and it is added by an address adder 5, supplied to a memory 7 through a decoder 6, and as a result, an instruction of the OS 9 can be fetched. In this way, the OS 9 which has obtained a control restores all registers which have been saved previously, and thereafter, can execute a necessary operation.
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