modeless command

As an example, the operate timing among 8237 working in the demand transfer mode,peripheral and CPU is also analyzed in detail,the logic design of implementing dual transfer mode is presented,and the process ability of DMA controller is widened.

并以 82 3 7DMA控制器为例 ,详细地分析了工作在命令传输方式的 82 3 7与外设、CPU之间的操作时序 ,提出了实现双数据传输方式的逻辑设计 ,拓宽了 DMA控制器的处理能