| 摘要 |
PURPOSE:To attain the DMA transfer of an external memory without discontinuing the working of an MPU by cutting a bus line reaching an external memory from a DMA controller from a main bus line in a DMA transfer mode. CONSTITUTION:A DMA controller 71 receives a DMA request signal DRQ1 from a controller 72 of a floppy disk device 6 and transmits a start signal DRQ2 to a timing circuit 76. A clock phi is supplied to the circuit 76 from an MPU1, and a prescribed period of time is counted based on the clock phi. Then a control signal K is outputted to a bus buffer control circuit 77. At the same time, a DMA permission signal GRNT is outputted to the DMAC71. The buffer controller 77 actuates a bus buffer 75 for a prescribed period of time by the clock phi given from the MPU1 as well as the signal K. Thus a system bus 4 is separated from a bus line 74. Then the transfer of data is started between a RAM73 and an FDC72 via the line 74. |
