DMA can run constantly or can be triggered by exterior interruption (INT3-0), interior interruption (timer and serial port), at the end of transfers, send interruptionsignal to CPU.
The interruption is a kind of signal, it tells that the microprocessor has already taken place a certain demand specially notices of affairs, need a whereabouts reason or contribute efforts to it.
中断是一种信号，它告诉微处理器已发生了某种需要特别注意的事件，需要去处理或为其服务。
3
The first frame (8) data sending finished, the control signal are restored the original state, only keep a high level, ti application state interruption.