异步和同步数据通信的区别及其特点

Asynchronous and Synchronous Data Transmission异步和同步数据通信

Over longer distances we use serial transmission either in an asynchronous or

synchronous transmission mode. Serial transmission over long distance requires

that the timing information for the receiver be transmitted together with the data so

that a separate clock signal is not required.

在长距离，我们用异步或同步传输模式进行串行传输。由于接受者需要定时信息，长

距离的串行传输为了避免单独传时钟信号需要把定时信息和数据一起传输。

In asynchronous transmission only a small number of bits are transmit ted at a

independently with the help of a new start bit preceding the data bits.

在 异步 传 输 时 ， 在同 一 时 候 只 有一小 数 量 二 进 制位 被 传 输 ， 通常 8 位 对 应 着 一 个

ASCII字符。在每个8位数据的前面，一个开始位被发送以暗示接收端要准备接收 8位数据

（如图6.2）。对于同步传输时，接收者必须要提前知道数据速率，然后当它发现开始位时 ，

它才能接收接着的二进制位。最后会在8位数据后面加一个停止位来结束。接着下一个数据

以新的开始位开始独立的同步传输。

In asynchronous transmission, a simple error-detecting scheme called parity

can be used. We may use even or odd parity error checking. If even parity is used,

the total number of “1” bits in the block, including data bits and the parity bit, is set to

be even with the help of the parity bit. In the case of odd parity, the parity bit is set to “1”

奇偶校验位的值决定要把其设置为偶数。假如是奇校验，奇偶校验位将被设置为 1或0，使

这个块的奇偶为奇。为了检查可能传输中出现的错误，接收端将检查接收到的 1的位的奇偶

是否符合奇偶校验。我们稍候将从一个简单得数据链路层协议中知道奇偶校验的方法。

Asynchronous transmission is used for the transmission of ASCII char acters in

conventional terminal–mainframe computer communications. For larger information

blocks it is used in some file transfer protocols such as KERMIT and X-LINK. In these

protocols special “start of block” characters are sent at the beginning. Then information