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What is serial port baud rate? Why do we need to set the baud rate for serial communication?

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Baud Rate

In the world of electronic devices, data is transmitted in various ways. Serial Baud Rate communication is a common method, known for its simplicity, reliability, and wide application, making it an essential means of communication between devices.

One crucial parameter in serial communication is the baud rate. Let’s explore why baud rates are set in serial communication.

  1. What is a Serial Baud Rate?

Firstly, we must understand what baud rate means. The baud rate measures the data transmission speed in units per second, indicating the number of symbols transmitted per second. Essentially, the baud rate is the “pulse” of the data, determining the speed of transmission.

Relationship between Baud Rate and Bit Rate:

Bit Rate = Baud Rate * Number of binary bits per modulation state.

With different modulation techniques, multiple bits of information can be carried on one symbol. In serial communication, where the transmitted symbols are bits, the baud rate equals the bit rate, which is numerically equivalent to the clock cycle.

  1. Why Set a Baud Rate in Serial Communication?

If the sender and receiver do not agree on a common baud rate, they cannot correctly interpret the data sent by each other, leading to communication failure. Therefore, setting the baud rate is key to ensuring successful serial wireless communication.

Calculating the Baud Rate:

Baud rates in serial communication, such as 9600, 19200, 38400, 57600, and 115200, are typically powers of two, reflecting the efficiency of computers in processing binary data.

There are two main methods to calculate the baud rate:

Direct Method: Measures the number of pulses transmitted within a unit of time, straightforward but requiring specialized testing equipment.

Indirect Method: Calculates based on the number of characters transmitted in a unit of time, less reliant on specialized equipment but more complex.

The baud rate can be calculated using the formula:

Baud Rate = Symbol Rate / (Number of bits per symbol)

Where:

Symbol Rate: The frequency of signal changes per symbol.

Number of bits per symbol: The number of bits represented by each symbol.

Choosing the Serial Baud Rate:

In practice, baud rates are often set and adjusted via software, with most programming languages offering functions or methods to easily configure these settings. Due to hardware and software limitations, the actual baud rate may be lower than the set rate, known as “baud rate error.” To minimize this, measures such as using high-quality serial cables and optimizing software algorithms can be taken.

The choice of baud rate should be based on specific communication needs. For smaller data volumes, a lower baud rate may suffice; for larger data volumes, a higher rate is necessary. Stability and interference resistance also play roles, where higher rates can improve these aspects but might increase hardware complexity and costs.

In addition to basic data transmission, serial communication can incorporate advanced features such as parity checks, data bit checks, and stop bit settings, which enhance reliability and stability.

Given its advantages, serial communication will continue to be widely used, making a deep understanding and mastery of baud rates essential for electronic engineers.

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