| 摘要 |
PROBLEM TO BE SOLVED: To discriminate a nonstandard device from a bus error exception by providing a proxy response circuit which makes a data transfer response as a substitute for the nonstandard device when the nonstandard device is not mounted, a proxy response address register, and a proxy response status register. SOLUTION: When a nonstandard device 13 is mounted, the nonstandard device 13 sends a data transfer response back at a data transfer request made by an MPU 11. In this case, the proxy response circuit 31 never sends data transfer back. When the nonstandard device 13 is not mounted, the proxy response circuit 31 sends a data transfer response back to the MPU 11 when a timer 32 counts up a prescribed time on condition that the data transfer request of the MPU 11 matches the address of the nonstandard device 13 stored in the proxy response address register 33, so that the data transfer will normally end. In this case, the proxy response status register 35 is read out to confirm that the proxy response is made.
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