甲机把一个字符及数据串向乙机发送。乙机收到开始信息后，把以后数据不停相加，收到停止信息以后，向甲机回传相加和。（带有protues仿真） -A machine to a character string and sends data to the B machine. B machine began after receipt of the information, the data is kept after adding the stop information received aft