异步通信的特点：不要求收发双方时钟的严格一致，实现容易，设备开销较小，但每个字符要附加2～3位用于起止位，各帧之间还有间隔，因此传输效率不高。 -Characteristics of asynchronous communication: does not require the sender and receiver clock strictly consistent and easy to implement, cost of equipment is small, but each c