STM32 - Communication

Communication classification

（1） Serial communication and parallel communication

Serial communication ： It refers to a small number of data signal lines between devices ( commonly 8 Below root ), Ground wire and control signal wire , A communication method that transmits data bit by bit in the form of data bits , Like a bicycle lane

Parallel communication ： Generally speaking, it refers to the use of 8,16,32, as well as 64 One or more data lines for transmission , It's like multiple lanes

characteristic	Serial communication	Parallel communication
Communication distance	Far away	Closer
Anti interference capability	Stronger	Weak
Transmission rate	slower	Faster
cost	The lower	Higher

（2） According to the direction of data communication , It can be divided into full duplex , Half duplex and Simplex Communications , It is mainly distinguished by the direction of the channel

full duplex ： At the same time , Two devices can send and receive data at the same time

Half duplex ： Data can be sent and received between two devices , But not at the same time

Simplex ： Only one direction of communication can be carried out at any time , That is, a fixed transmission device , The other is fixed as a receiving device

（3） According to the data synchronization mode of communication , It is divided into synchronous communication and asynchronous communication

Generally, it can be based on the communication process , Whether the clock signal is used for simple differentiation

  High efficiency of synchronous communication , But the requirements for clock synchronization of both sides are high

Communication rate

  A very important parameter to measure the communication performance is the communication rate , Usually expressed in bit rate , And the binary number transmitted per minute , In bits per second (bit/s), Bityes 2 States ,0 perhaps 1

Baud rate ： Indicates how many symbols are transmitted in seconds , The unit is baud/s, Symbol is the concept of communication signal modulation , A code can be represented by multiple binaries , For example, define a communication method 1 A symbol a use 2 individual bit Express , If 1 One symbol per second , So the baud rate is 1, The bit rate is 2, When the bit rate is equivalent to the baud rate , Default 1 For symbols 1 individual bit Express , namely 1 potter =1 Code element

USART—— Communication synchronous asynchronous transceiver

UART The period is mainly used for Generate protocol signals of relevant interfaces , Such as RSC232/RS485 Serial interface standard specification and bus standard specification , Use these interfaces to transmit data , It is necessary to send data according to the protocol signal specified by the interface , therefore UART Devices are widely used in serial communication , Play the role of folding conveyor

STM32 and PC adopt RS-232 Standard communication

 

 RS-232 It is the standard for serial data communication formulated by the American Electronic Industry Alliance , It is widely used in computer serial interface peripheral connection ,RS-232 The standard specifies connecting cables and machinery , Electrical characteristics , Signal function and transmission process

Generally, the comment mark used on the development board can be different from the comment standard used in communication , such as TTL Standards and RS-232 standard

Communication standards	Level standard （ The sender ）
5V TTL	Logic 1：2.4V~5V Logic 0：0~0.5V
RS-232	Logic 1：-15V~-3V Logic 0：+3V-+15V

Because controllers generally use TTL Level standard , So we often use MA3232 chip （ Level conversion chip ） Yes TTL as well as RS-232 Level signals are converted to each other

RS-232 Standard data transfer protocol layer

The data packet of serial communication is sent by the sending device through its own TXD Interface to the receiving device RXD Interface , In the serial communication protocol layer , Specifies the content of the packet , Including the start bit , Subject data , The check bit is composed of stop bits , The data packets of both communication parties should be agreed to be consistent in order to send and receive data normally

  Concept of agreement

Baud rate ： There is no clock signal in asynchronous communication , Therefore, the baud rate needs to be agreed between the two communication devices , That is, the length of each symbol , To decode the signal , The common baud rate is 4800,9600,115200 etc.

Start and stop signals of communication

A packet of serial communication starts with the starting signal , Until the stop signal is over , The starting signal of the data packet consists of a logic 0 The data bits of the , The stop signal of the data packet can be 0.1,1,1.5, or 2 A logic 1 The data bits of the , As long as both parties agree

Valid data

The main data content to be transmitted is immediately followed by the start bit of the packet , Also known as valid data , The length of valid data is often agreed as 5,6,7,8 Bit length

data verification

After the valid data , There is an optional data bit check , Because data communication is relatively vulnerable to external interference, resulting in transmission data deviation , This problem can be solved by adding check bits in the transmission process , The verification method includes parity ,0 The checksum 1 Check and no check

Use CubeMX Configure serial port

 （1） First set the clock

 

 

 （2） Set up the system SYS

（3） Set the serial port

  The default pin is PA9 and PA10, Can be modified according to your own needs , Here, according to USB The serial port diagram is changed to PB6 and PB7

  Set interrupt enable

  It has been set up here , You can generate layer code