| 摘要 |
PURPOSE:To improve the noise resistance and reliability of an extended bus controller by automatically detecting whether a peripheral equipment control circuit to be an object for DMA transfer is connected to the inside or outside of the device and controlling the direction of a data buffer in accordance with a detected result. CONSTITUTION:When the peripheral equipment control circuit is connected to the inside, a DMA transfer request is directly transmitted to a system through an internal DMA request signal 1. Thereby, an external DMA request signal 2 is not turned to '0' and a flip-flop 5 is not set up. The outputs of AND gates (I)6, (II)7 are reversed to a case connecting the peripheral equipment control circuit with the external. When the direction of the data buffer 8 is controlled by using the outputs of the two AND gates 6, 7, the connection of the peripheral equipment control circuit to the inside or the outside can be automatically detected at the time of extending a system bus including DMA transfer to the outside, so that the direction of the data buffer 8 can be controlled. |
