What isstart bit

If you are new to communication protocols, it can be overwhelming to understand how they work and what each term means. One of the most important concepts in serial communication is the start bit.

What is a Start Bit?

A start bit is the initial bit in a serial data transfer that indicates the start of a new character. It is always binary 0 and informs the receiver that the information it is about to receive is valid.

How Does a Start Bit Work?

After receiving a start bit, the system recognizes that there will be a certain number of character bits (defined by the bits per character parameter) and possibly a parity bit (specified by the parity parameter) before receiving the stop bit (binary 1).

The start bit is crucial in proper synchronization between the transmitting and receiving devices. It allows the receiver to know when to start reading the bits and when to expect a new character.


The start bit plays a vital role in serial communication, and without it, the data transmission will be unreliable. Understanding the basics of communication protocols such as start bits is necessary for efficient and error-free data transfer.


What happens if the start bit is missing?

If the start bit is missing, the receiving device will not be able to synchronize the transmission and will likely receive the wrong data.

What is the purpose of a stop bit?

The stop bit signifies the end of a character and allows the receiving device to prepare for the next character.

Are start and stop bits used in all communication protocols?

No, not all communication protocols use start and stop bits. Some protocols use other methods, such as synchronization through a clock signal.

The Bottom Line

Knowing the fundamentals of communication protocols, including start bits, is essential for anyone working with serial data transfer. A clear understanding of these basics is necessary for efficient and reliable data transmission.

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