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

What is baud rate?

Baud rate is a term used in electronic communications to describe the data transmission speed of a channel. The so-called channel can be wireless or wired. The baud rate represents the number of symbols transmitted per unit time. It is a measure of the symbol transmission rate. It is expressed by the number of changes in the carrier modulation state per unit time. The baud rate refers to the number of symbols transmitted per unit time. The number of transmitted symbols.

The usual unit of baud rate is bit/s, which is binary bits/second. Because a byte is 8 bits, and a byte can usually express an ASCII code, such as an English letter, so: a channel with a baud rate of 9600 can theoretically transmit 9200/8 English letters per second. , which is 1200 bytes, about 1.2KB. The 19200 can transmit 2400 bytes per second. For example, if a file has a capacity of 100KB, it will take at least 100/1.2 seconds to transmit it through the 9600 channel, which is more than a minute.

The difference between baud rate 9600 and baud rate 19200

1. Different speeds

1. Baud rate 9600: 9600/8 English letters can be transmitted per second.

2. Baud rate 19200: 19200/8 English letters can be transmitted per second.

2. Different transmission volumes

1. Baud rate 9600: 1200 bytes can be transmitted per second, about 1.2KB.

2. Baud rate 19200: 2400 bytes per second, 2.4KB.

3. Different characteristics

1. Baud rate 9600: Use its RXD and TXD to communicate with the outside world. There are two physically independent receiving and transmitting buffers SBUF inside, which can send and receive data at the same time.

2. Baud rate 19200: The overflow rate is divided by two (or not) and then divided by sixteen as a shift pulse for serial transmission or reception.

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

There are two more reliable ways to say it:

1. Based on the physical characteristics of electricity, transmission media, etc. combined with the requirements for the use of serial device

In order to ensure effective communication, based on the physical characteristics of electricity and transmission media combined with the requirements for the use of serial port equipment, it is determined that the maximum transmission rate of RS232 can only be 115200, and then divided into two levels step by step to obtain 57600, 28800, 19200… In order to adapt to these rates, the corresponding design the crystal oscillator frequency.

2. This is determined by the characteristics of telecommunications lines

The bandwidth of the bandpass filter used in telephone lines is 3KHz (300~3300Hz). At that time, the “father of Wi-Fi” Vic Hayes (Vic Hayes) used a 2400HZ signal when making a modem, and the corresponding baud rate was 2400. Since the basic frequency has been determined, the methods used in the future to increase the communication rate will all be multiplied on the basis of 2400, so 9600, 19200…

Trefwoorden: serial port module