Synchronous Vs Asynchronous Digital Design

What are Synchronous and Asynchronous?

Synchronous and asynchronous transmissions are two different methods used in digital systems for synchronization of transmitter and receiver during data transfer. Synchronous transmissions are synchronized by an external clock, while asynchronous transmissions are synchronized by special signals along the transmission medium.

What is the Need of Synchronization?

Whenever an electronic device transmits digital (and sometimes analog) data to another electronic device, there must be a certain rhythm established between the two devices, i.e., the receiving device must have some way of knowing, within the context of the fluctuating signal that it’s receiving, where each unit of data begins and where it ends.

For example, a television transmitter produces a continuous stream of data in which each horizontal line of image must be distinguishable from the preceding and succeeding lines, so that a TV will be able to distinguish between them upon reception.

So the signal must be synchronized in a way that the receiver can understand the data format and receive the data correctly from the transmitter.

What are the Advantages of Asynchronous data transfer?

• Simple. It doesn’t require synchronization of both communication sides
• Cheaper. Timing is not as critical as for synchronous transmission, therefore hardware can be made cheaper
• Set-up is very fast, so well suited for applications where messages are generated at irregular intervals, for example data entry from the keyboard

What are the Limitations of Asynchronous data transfer?

• Large relative overhead, a high proportion of the transmitted bits are uniquely for control purposes and thus carry no useful information

What are the Advantages of Synchronous data transfer?

• Lower overhead and thus, greater throughput
• Synchronous designs eliminate the problems associated with speed variations through different paths of logic. By sampling signals at well-defined time intervals, fast paths and slow paths can be handled in a simple manner.
• Synchronous designs work well under variations of temperature, voltage and process. This stability is key for high-volume manufacturing.
• Many designs must be portable—that is, they must be easy to migrate to a new and improved technology (say, moving from .6 micron to .35 micron). The deterministic behavior of synchronous designs makes them much more straightforward to move to a new technology.
• Interfacing between two blocks of logic is simplified by defining standardized synchronous behavior. Asynchronous interfaces demand elaborate handshaking or token passing to ensure integrity of information; synchronous designs with known timing characteristics can guarantee correct reception of data.

What are the Limitations of Synchronous data transfer?

• Slightly more complex
• Hardware is more expensive