Differences between synchronous communication and asynchronous communication

Synchronous communication principle

Synchronous communication is a continuous serial transmission of data. Only one frame of information is transmitted at a time. The Information Frame here is different from the character frame in asynchronous communication. It usually contains several data characters.

When synchronous communication is used, many characters are combined into an information group so that the characters can be transmitted one by one. However, synchronization characters must be added at the beginning of each group of information (usually referred to as frames, when there is no information to transfer, fill in the above characters, because synchronous transmission does not allow clearance. During synchronous transmission, a character can correspond to 5 ~ 8 bits. Of course, for the same transmission process, all characters correspond to the same digit, for example, N digits. In this way, each n-bit is divided into a time slice. The sender sends one character in a time slice, and the receiver receives one character in a time slice.

During synchronous transmission, a message frame contains many characters, and each information frame starts with a synchronous character. Generally, the synchronous character and null character are used in the same code. In the whole system, the same code is used for sending and empty characters controlled by a unified clock. The receiving end should certainly be able to recognize synchronous characters. When a string of digits matches the synchronous characters, it is considered that an information frame starts, process the subsequent digits as the actual transmission information.

Asynchronous Communication Principle

Asynchronous Communication is a common communication method. During asynchronous communication, the interval between sent characters can be arbitrary. Of course, the acceptor must always prepare for receiving. The sender can start sending characters at any time. Therefore, a flag must be added at the beginning and end of each character, that is, the Start and Stop bits must be added, so that the acceptor can correctly receive each character. The advantage of asynchronous communication is that the communication device is simple and cheap, but the transmission efficiency is low (because the overhead of the Start bit and stop bit accounts for a large proportion ).

Differences between synchronous communication and asynchronous communication:

1. synchronous communication requires that the receiver's clock frequency be the same as the sender's clock frequency, and the sender sends continuous bit streams. In asynchronous communication, the receiver's clock is not required to be synchronized with the sender's clock, after sending a byte, the sender can send the next byte at any long interval.
2. High synchronization efficiency; low asynchronous communication efficiency.
3. synchronous communication is complex, and the allowable clock error of both sides is small. asynchronous communication is simple, and the clock of both sides can allow a certain error.
4. synchronous communication can be used for point-to-point communication. asynchronous communication is only applicable to point-to-point communication.