Asynchronous communication vs Synchronous communication

This page asynchronous communication vs Synchronous communication describes difference between Asynchronous communication and Synchronous communication.

asynchronous communication

In the case of asynchronous communication, each data word is accompanied by start bit at the beginning of the transmission and stop bit at the end. Each binary code word represents one character.

Low speed data communications of upto 115 K baud is possible with asynchronous communication. It is referred as most reliable due to presence of start and stop bits. These start and stop bits effectively slows down the data transmission.

synchronous communication

In the case of synchronous communication, each data word is transmitted one after the other without the use of start and stop bits. For synchronization purpose, group of synchronization(SYN) bits(unique pattern of bits) are placed at the beginning and special code(e.g. ETX) signaling is placed at the end of the block. SYN bits are 8 bits each. Here each block represent hundreds/thousands of characters. ETX help receiving equipment identify end of the block transmission.

Although SYN and ETX are added along with the data to be transmitted, they represent less amount compare to Start and Stop bits used in the case of synchronous transmission. Hence Synchronous communication is faster way of data communication compare to the asynchronous communication.

Following table summarizes difference between Asynchronous communication and Synchronous communication.

Specifications Asynchronous communication Synchronous communication
Method uses serial mode of communication uses parallel mode of communication,
Refer Serial vs Parallel.
Distance Coverage longer shorter
Sync. technique Using start bit (at beginning) and stop bit (at end) Using clock
transmission capacity transmits 1 character at a time transmits multiple characters (in the form of block) at a time.
Speed It has lower speed compare to sync. transmission due to bitwise serial transmission. It has higher speed compare to async. transmission due to parallel multi-bit transmission.
Cost cheaper costlier due to transmission mechanism

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