说明：  主要讲解数据编码和解码原理，还有数字数据转换后通过模拟方式发送，模拟数据转换后以数字的方式传输的原理。
(Mainly on the principle of data encoding and decoding, as well as digital data converted by simulating the way to send, after the analog data converters to digital transmission of the tenets of the way.)