Cable = charging line, line indicates charging cable, what reason is this?

Most of the time we spend low price bought a cable back found that it can only charge, unable to transmit data. So, choose one of cable to charging and data transmission. If buy a far-fetched 'data line', often can only charge cannot transfer data. What is going on here? < / p > the reason: data line is mainly composed of ground wire ( By zero line, the black wire) And read the data line, Signal wire, connect the green wire) And writing data line ( Signal into line, white wire) , + 5 v line ( Positive, press the red wire) Four lines; Charging line generally in order to save costs, may leave out the middle of two lines, namely to eliminate the read and write data and data line, also is not the ability to read and write data, only have cell phone charging function. < / p > < / p > < p > < / p >