Asynchronous transmission
Asynchronous Transmission Definition
Asynchronous transmission is a method of transmitting data where individual characters are sent one at a time, with the sender and receiver using their own independent clocks to determine the timing of each bit. Unlike synchronous transmission, which requires synchronized timing between the sender and receiver, asynchronous transmission sends data in frames composed of a start bit, data bits, an optional parity bit for error checking, and a stop bit.
How Asynchronous Transmission Works
In asynchronous transmission, the data is divided into frames, each of which includes a start bit, data bits (usually 7 or 8), an optional parity bit, and a stop bit. These elements work together to ensure the successful transmission and reception of data:
Start Bit: The start bit signals the beginning of a new character and synchronizes the receiver's clock with the sender's clock. It is always low (0) and helps the receiver adjust its internal clock to match the sender's clock.
Data Bits: The data bits contain the actual information being transmitted. They can be 7 or 8 bits long per character, depending on the encoding scheme being used. The exact number of bits is determined by the character set and the specific protocol.
Parity Bit: An optional parity bit can be included for error checking in asynchronous transmission. The parity bit is set to 1 or 0 based on a preset rule (odd or even parity), allowing the receiver to detect errors that may have occurred during transmission. If the receiver detects an error in the parity bit, it can request a retransmission of the data.
Stop Bit: The stop bit is used for synchronization and indicates the end of the data frame. It is always high (1) and allows the receiver to resynchronize its clock for the next character. The stop bit ensures that the receiver is ready to receive the next character and prevents overlapping of data.
Advantages of Asynchronous Transmission
Asynchronous transmission offers several advantages in data communication:
Flexibility: Asynchronous transmission allows data to be sent at irregular intervals, making it suitable for applications where transmission times may vary. It does not rely on a fixed clock speed like synchronous transmission.
Efficiency: Asynchronous transmission only requires a single wire for data and does not need constant synchronization between the sender and receiver.
Error Detection: The inclusion of a parity bit in asynchronous transmission enables error detection, improving data integrity.
Compatibility: Asynchronous transmission can be used with a wide range of devices and protocols, making it highly compatible.
Disadvantages of Asynchronous Transmission
Despite its advantages, asynchronous transmission also has some limitations:
Slower Speed: Asynchronous transmission is generally slower compared to synchronous transmission due to the additional bits required for start, stop, and optional parity.
Overhead: The inclusion of start, stop, and parity bits in each frame adds extra overhead to the transmission, reducing the overall efficiency.
Error Detection, Not Correction: While asynchronous transmission employs a parity bit for error detection, it does not have the capability to correct errors. If an error is detected, the receiver will typically request retransmission of the data.
Use Cases and Examples
Asynchronous transmission is commonly used in various applications and industries. Some examples include:
1. Serial Communication: Asynchronous transmission is widely employed in serial communication interfaces, such as RS-232, to transmit data between devices.
2. Keyboard and Mouse Communication: Asynchronous transmission is used in keyboard and mouse interfaces to send keypresses and cursor movements to a computer.
3. Modem Communication: Asynchronous transmission is utilized in modem communication to transmit data over telephone lines.
4. Terminal Emulation: Asynchronous transmission is used in terminal emulation applications to emulate the behavior of traditional serial terminals.
Asynchronous transmission is a method of data transmission that sends individual characters one at a time, with the sender and receiver using their own clocks to determine the timing of each bit. It offers flexibility, error detection, and compatibility, but it is generally slower and has more overhead compared to synchronous transmission. Asynchronous transmission finds applications in various industries, including serial communication, keyboard and mouse interfaces, modem communication, and terminal emulation. By understanding the principles and applications of asynchronous transmission, we can better comprehend and utilize this essential aspect of modern data communication.
Related Terms
- Synchronous Transmission: A method of data transmission where data is sent in synchronized blocks.
- Bit Rate: The rate at which bits are transmitted, received, or processed per unit of time.
- Parity Bit: A type of error-checking bit used in asynchronous transmission to detect errors in data.