异步传输一般以字符为单位，不论所采用的字符代码长度为多少位，在发送每一

异步传输

字符代码时，前面均加上一个“起”信号，其长度规定为1个码元，极性为“0”，即空号的极性；字符代码后面均加上一个“止”信号，其长度为1或者2个码元，极性皆为“1”，即与信号极性相同，加上起、止信号的作用就是为了能区分串行传输的“字符”，也就是实现了串行传输收、发双方码组或字符的同步。-Asynchronous transfer in characters, irrespective of the length of the character code for the number of bits, in transmitting each asynchronous transmission character code, are coupled in front of a " from"　signal, and its length is defined as one symbol, polar behind the character code is " 0" , i.e., empty No. polarity　plus a " stop"　signal, and its length is one or two symbols, the polarity are all " 1" , i.e. the same as the signal polarity, plus on from the stop signal is to be able to distinguish between serial transmission " character" , that is, to achieve a resumption of serial transmission, synchronization hair both code groups or characters.