Communication protocol -- Classification and characteristics Introduction

One 、 Baud rate

In the field of electronic communication , potter （Baud） Modulation rate , It refers to the rate at which the effective data signal modulates the carrier , That is, the number of carrier modulation state changes per unit time . Baud rate indicates the number of symbols transmitted per second , It is a measure of symbol transmission rate , It is expressed by the number of carrier modulation state changes per unit time ,1 Baud rate refers to the transmission rate per second 1 Symbols .

Two 、 Asynchronous and synchronous

asynchronous ： There is no clock line between the two devices , But both sides of the equipment need to maintain the same communication baud rate , Here's the picture , There is no data cable SCL Clock line .

Sync ： Sometimes the clock line , Same communication speed , Therefore, it is no longer necessary to configure the same speed . Here's the picture , In addition to the data line for exchanging information , also SCL Clock line .

3、 ... and 、 full duplex 、 Half duplex 、 Simplex

（1） Simplex

Two communication devices are connected by one wire , And only communicate in one direction . Here's the picture , Data from A To B One direction communication .

（2） Half duplex

The two devices are connected by a wire , Data can be transmitted on both sides , But at some point , Data can only be transferred from one party to the other .

（3） full duplex

There are two data cables , At the same time ,A to B Sending data ,B You can also ask A Sending data . Here's the picture .

3、 ... and 、 Serial and parallel

parallel ：

Multiple bit At the same time , Data transmission is based on the word length of the computer , Usually 8 position 、16 position 、32 Bit is the transmission unit , Transmit data one word at a time . It is suitable for external devices and CPU Close information exchange between . At the same frequency , The efficiency of parallel port transmission is several times that of serial port .

Serial ：

Data is transmitted bit by bit in sequence , The receiving end is also grounded bit by bit .

Four 、 Classification of common interface technologies

1-Wire/W1/ First line agreement , Typical representatives are DS18B20 Temperature sensor 、DHT11 Temperature and humidity sensor ;
I2C/IIC agreement , Typical representatives are SHT30 Temperature and humidity sensor 、OLED display 、RTC、 Touch screen, etc. ;
UART/RS232/RS485/ Serial protocol , Typical representatives are GPS、GPRS/3G/4G、NB-IoT、 bluetooth 、WiFi Equal module ;
SPI agreement , Typical representative NFC chip 、SPI Ethernet 、LoRa etc. .

5、 ... and 、 Level signal and differential signal

Level signal and differential signal are used to describe the transmission mode of communication line , That is, how to express on the communication line 0 and 1.

Level signal ： There is a reference level line in the transmission line （ It's usually GND）, Then the signal value on the signal line is determined by the voltage difference between the signal line level and the reference line ; The disadvantage is that it is easily disturbed , Like thunder or something , The signal line is affected , The signal line level changes greatly , Then the voltage difference between the signal line level and the reference line level will change greatly .

Differential signal ： There is no reference level line , All are signal lines （D+,D-）, The transmission quality is stable . Because if you change, the two wires will change together , The difference between the two lines has not changed , So it doesn't matter much .