| 摘要 |
PURPOSE:To prevent the occurrence of a memory access where a channel exceeds a page, by stopping the prefetch request from a memory requesting circuit when the boundary of the page is detected by a page boundary detecting circuit. CONSTITUTION:If a memory address counter 100 exceeds the boundary of one page in a virtual storage space to designate an address higher than a prescribed address during the execution of data transfer control, the signal of a prescribed bit on the counter 100 is changed from ''0'' to ''1''. As the result, a D type FF constituting a page boundary detector 120 is set by signal ''1'' of the memory address, and the inverted Q output signal is reduced to ''0''. Consequently, a gate circuit 130 is closed after this time to inhibit the output of a memory request signal MREQ. Thus, prefetch of data stored in a main memory is stopped. Meanwhile, the transfer of data stored in a data buffer is terminated when the number of bytes of data transferred to an I/O device reaches a prescribed value |
