Answer to Question #273612 in Electrical Engineering for Anil

Question #273612

What do you mean by Asynchronous Transfer Mode? Explain the various types of Asynchronous Transfer Modes with suitable diagrams.

Expert's answer

Serial Communication:

Serial communication is bit by bit transmission from sender to receiver. The serial transmission is of two types:

Synchronous Transmission - Examples are SPI, I2C

Asynchronous Transmission or Universal Asynchronous Transmission (UART): RS-232 transmission

In case of asynchronous transmission, the sender keeps on dumping the bits to the receiver irrespective of receiving any bits from the receiver. That is why it called asynchronous transmission. RS-232 is popular example of UART. The UART transmission can take place over 9 ft. distance of sender and receiver.

When there is no UART communication, the data bus is held at logic level HIGH. The UART communication starts by making LOW at data bus and it indicates the start bit. Start bit is the first bit in one byte UART transmission/communication. Start bit is normally at logic level LOW.


Next 8 bits are data bits that are transmitted just after the start bit.


After 8 data bits, next bit is the parity bit.


And in the last, Stop bit is the last bit in one byte UART transmission/communication. Stop bit is normally at logic level HIGH.


If an UART port is set up for: 8 bit data, 1 odd parity bit, 2 stop bits, and baud rate 115200 bps.

Baud rate is the speed of UART communication. Therefore the baud rate of 115200 bps, indicates that 115200 bits are transmitted over UART in 1 second.

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