SCM learning notes 9 -- common communication methods (based on Baiwen STM32F103 series tutorials)

Chapter nine Common communication methods

Communication is data transmission , Send or receive data between different modules . Therefore, the communication mode can also be considered as the data transmission mode . The common communication methods are as follows .

One 、 Serial and parallel communication

The simple difference between serial and parallel is whether the data transmission line is one or more .

1、 serial communication

Serial communication is to use one line for data transmission , All the data is strung together , Series connection in similar circuit .

One clock transmits one data , For the picture above 0x5ABC Come on , want 16 It takes a clock to send .

The advantage of serial communication is that less resources are used , Only one thread is needed , The cost is low . The disadvantage is that the transmission speed is slow , A clock can only pass one bit, But with the development of Technology , Now the speed of serial communication is faster and faster , It can meet most scenarios , So in the actual development , We prefer serial communication . However, data loss may also occur in serial communication .

2、 Parallel communication

Parallel communication uses multiple lines for data transmission , A clock transmits multiple data through multiple lines , Parallel connection in similar circuits .

Above, 8 Parallel communication of lines , It can be transmitted at one time 8 individual bit, This is also transmission 0x5ABC, It only takes two clock cycles .

The advantage of parallel communication is high transmission speed . The disadvantage is high cost , Unable to use long-distance scenes , And too many parallel lines will cause signal interference .

Two 、 Synchronous and asynchronous communication

The difference between synchronization and asynchrony depends on whether the working frequency of the sender and the receiver are consistent , Consistency is synchronization , Inconsistency is asynchronous . The simple understanding is whether the two sides are Under the same clock standard Data transfer , That is to see whether the clock lines are sometimes connected between the two sides .

1、 Synchronous communication

Both parties are under the control of the same clock signal , Receive and send data , A clock , The sender sends , The receiver receives , Their working state is consistent with each other .

The data frame composition of synchronous communication is generally ： Synchronous signal + Some data . At the front is a synchronization signal , After the receiving end receives the data and analyzes the synchronization signal , It is considered that the data behind are actually transmitted . Theoretically, the number of bits of several data in a data frame of synchronous communication is unlimited .

In synchronous communication , There can be no interval between data , Because both sides work under the same clock , It's on this side , It must be sent by the other side . After the synchronization signal , Think that all data are actual data , So when there is no information to transmit , The synchronization signal should be filled with the characters above .

2、 asynchronous communication

Asynchronous communication when sending characters , The time interval between transmitted characters can be arbitrary . Because every frame of data has start and stop bits , The data bits between them are the actual data . So the way for the receiver to judge whether the data is a complete frame of data is to analyze the start bit and stop bit in this pile of data .

The sender can start sending characters at any time , The receiving end must be ready for receiving at all times .

Because every data frame transmitted will have a start bit and a stop bit , The actual data generally only accounts for 5-8 position , This leads to the low transmission efficiency of asynchronous communication .

3、 ... and 、 Simplex 、 Half duplex 、 Full duplex communication

The difference between them is that at the same time , Whether the device can send and receive data .

1、 Simplex

The device can only send data or receive data . That is to say, he There is only one function , Or you can only send data , Or you can only receive data . It's like a radio , He can only receive external data and cannot send data to the outside .

2、 Half duplex

Half duplex indicates that the device has two functions , It can send data , And can accept data , But in At the same time He can only use one of these functions , Cannot receive data when sending data , You cannot send data when receiving data . Like a walkie talkie , Listening and speaking are separate , You can only choose to speak or listen to others at the same time .

3、 full duplex

Full duplex can be compared with the above two at the first glance , It's the best . In full duplex communication mode , Equipment in At the same time , It can send and receive data . It's like a cell phone , While speaking, you can also hear others' voices .

Four 、 Communication rate

For synchronous communication , The communication rate depends on the clock signal , The faster the clock signal , The faster the communication speed .

For asynchronous communication , Both sending and receiving sides should have the same communication rate , Otherwise, the data will be garbled . such as 1S Inside , The sender sent 100 Data , But the receiver 1S Can only receive 50 Data , It's lost 50 Data .

There are usually two units to describe the communication rate , Bit rate and baud rate .

The bit rate is transmitted by the subsystem in unit time bit The number of , use Rb Express , The unit is bit/s, Abbreviation for bps

Baud rate is the number of symbols transmitted by the system in unit time , use RB Express , The unit is porter Bd.

A symbol is the level value on a data line , For example, there are only 0V and 5.5V Two kinds of state , Then the symbol has 2 States ; Yes 0V,3.3V,5V Three states , There are symbols 3 States .

The relationship between bit rate and baud rate ：$x_i^2$Rb = RB * log2（N）;N Is the state of the symbol .

5、 ... and 、 Common communication protocols

In actual development , According to the product requirements, from the performance 、 cost 、 Stability and other factors .