What is the Difference Between Synchronous and Asynchronous Data Transfer

In synchronous data transfer, the transmitter and the receiver are synchronized with the same clock pulse. In asynchronous data transfer, the transmitter and the receiver do not use a common timing signal. That is the main difference between synchronous and asynchronous data transfer.

Data transferring is the process of sending data from the transmitter (sender) to the receiver. It can be synchronous or asynchronous. Synchronous data transfer uses synchronized clocks to transmit data. In contrast, asynchronous data transfer uses a flow control method of sending start and stop bits with data.

Key Areas Covered

1. What is Synchronous Data Transfer
     – Definition, Functionality
2. What is Asynchronous Data Transfer
     – Definition, Functionality
3. What is the Difference Between Synchronous and Asynchronous Data Transfer
     – Comparison of Key Differences

Key Terms

Asynchronous Data Transfer, Synchronous Data Transfer

What is Synchronous Data Transfer

In synchronous data transfer, the transmitter and the receiver are synchronized and uses a common timing signal. It uses timing signals for synchronization. Here, the data flows as a continuous stream one after the other. The transmitter sends data, and the receiver counts the number of bits in the received data. Furthermore, there are no gaps between data. In this method, the timing signals must be accurate to transfer data efficiently. Moreover, this method is faster than asynchronous data transferring.

Figure 1: Synchronous and Asynchronous Data Transfer

In a digital system, if the other registers share the same clock with the CPU registers, the data transferring between the CPU and input and output devices is a synchronous data transfer. Both these units obtain the clock pluses from the common pulse generator.

What is Asynchronous Data Transfer

In asynchronous data transfer, the transmitter and receiver operate at different clock frequencies. It uses the start and stop bits to the data. According to the above example (figure 1), each byte of data is embedded in start and stop bits. The ‘0’ indicates the start bit while ‘1’ indicates the end bit. The ‘1’ and ‘0’ highlighted in red are the start and stop bits. Furthermore, timing is not an important factor in asynchronous data transfer.

In a digital system, if the other registers and CPU registers use their own private clocks, they have different timing signals. Therefore, the CPU and input and output devices should coordinate to transfer data. It is called an asynchronous data transfer.

Difference Between Synchronous and Asynchronous Data Transfer

Definition

Synchronous transfer is the data transfer method that sends a continuous stream of data to the receiver using regular timing signals that ensures both transmitter and receiver are synchronized with each other. Conversely, Asynchronous Data Transfer is the data transfer method that sends data from transmitter to receiver with parity bits (start and stop bits) in uneven intervals. Thus, this explains the fundamental difference between synchronous and asynchronous data transfer.

Clocks

In synchronous data transfer, the sender and receiver operate on the same clock frequencies whereas in asynchronous data transfer, the sender and receiver operate on different clock frequencies. Hence, this is the main difference between synchronous and asynchronous data transfer.

Data Transferring Speed

Data transferring speed is another difference between synchronous and asynchronous data transfer. Synchronous transfer is faster than asynchronous transfer.

Start and Stop Bits

There is no overhead of extra start and stop bits in synchronous transfer. On the other hand, asynchronous data transfer uses start and stop bits.

Gaps between Data

In synchronous data transfer, there are no gaps between data, and data flows as a continuous stream. However, in asynchronous data transfer, there can be gaps between data.

Time Intervals

Synchronous transfer uses constant time intervals. In contrast, asynchronous transfer uses random or irregular time intervals. This is another difference between synchronous and asynchronous data transfer.

Examples

For example, chat rooms and video conferencing use synchronous data transfer while emails use asynchronous data transferring.

Conclusion

The main difference between synchronous and asynchronous data transfer is that in synchronous data transfer, the transmitter and the receiver are synchronized with the same clock pulse while in asynchronous data transfer, the transmitter and the receiver do not use a common timing signal.

Reference:

1. Synchronous Data Transfer | COA, Education 4u, 11 Dec. 2017, Available here.
2. Asynchronus Data Transfer, Education 4u, 17 Apr. 2018, Available here.