The methods of serial data transmission imply that data are transmitted the following way: data are transmitted from transmitter to receiver bitwise simultaneously uing only one line.For this purpose the serial port takes 8, 16 or 32 parallel bits from the data bus and transforms them to get 8, 16 or 32-bit serial bit flow. That's why serial communication got its name - every information bit is transmitted serially one by one.

In theory when organizing serial communication to transmit the signal from one device to another one should use only two wires - signal and ground. But practical work shows that this way of data transmission is not always usable, especially when data transmission is lengthy. It is connected with the fact that when receiving, the receiver may miss some bits and so they may be lost. This would cause changes in the result of the whole transmission. Even if one bit is lost, this may cause the following: when the whole data batch is received the bits coming after the lost bit may be shifted and erraneous data may be obtained when transforming into parallel code.

That's why in order to achieve reliable serial communication one should overcome all possible errors when receiving data.One of the possible solutions may be application of RS-232-C standard which describes the methods of synchronous and asynchronous data transmission in serial data format.