| 摘要 |
PURPOSE:To prevent contents of a system memory from being rewritten by providing a memory with a write gate, setting the write gate with the aid of a DMA control signal being the output of a DMA control circuit so as to inhibit writing in the memory and also inhibiting the write gate from being reset. CONSTITUTION:A gate 8c that is controlled by the DMA control signal being the output of the DMA control circuit 4 and suppresses a write signal in the system memory 3, and a gate 8b that inhibits a write signal transmitting part 8a from being reset after the system memory 3 is accessed are provided. When the DMA control circuit 4 outputs the DMA control signal, the gate 8c suppresses the transmission of the write signal in the system memory 3 even if said memory is accessed, and the gate 8b suppresses a reset signal transmitted after the access to the system memory 3 ends. Thus the mistaken writing that is often found in a conventional system can be eliminated. |
