| 摘要 |
<p>PURPOSE:To use a memory with high efficiency by providing a switch between an 9-bit external device and the memory to perform switching between high- order and low-order data bases and controlling the switch according to the access address conditions. CONSTITUTION:When a data transfer request is delivered to a DMA controller 4 from an external device 9, an address is delivered for access to a memory 6 or 7 and a DMA operation is started. When an address output designates lower 8 bits, the data are transferred between the device 9 and the memory 6 via a data bus changeover switch 8, a data bus 12 for low-order 8-bit data and a 16-bit address bus 10. When an address of high-order 8-bits is designated, a control signal 13 is delivered. Thus the switch 8 changes the bus to a data bus 11 of high-order 8 bits. As a result, the transfer of data is possible between the memory 7 and the device 9.</p> |
