Can communication test based on STM32: turn the globe

Although it was right very early CAN I have heard of the agreement , But I have never had a chance to explore , So like many people , Yes CAN Our cognition only stays at “ Communication used in the automotive field ”. Because I have been looking at lithium batteries recently BMS：

The content involves CAN signal communication , And I will also hear some from customers at work J1939、NMEA2000 etc. , So I felt it was time to understand CAN 了 .

One 、CAN

Controller area network （Controller Area Network）, It was originally developed specifically to solve the serial communication of passenger cars , It has high real-time processing ability 、 High reliability and good error detection ability under strong electromagnetic interference . Its main purpose is to simplify the control connection between electronic control units in the car , cost reduction .CAN Each communication node in the protocol is usually composed of a controller and a transceiver ：

This communication structure is non master-slave , That is, any node can speak freely on the bus , The biggest problem with broadcast communication is that there is no object , Each node always selects the message that it cares about on the bus to receive , Then process , Filter out what you don't care about . That's the question , How do nodes distinguish messages ？ This is actually where I was confused at the beginning , Until you understand the arbitration domain in the message frame .

Two 、 message

CAN The message frame of is divided into standard frame and extended frame , That is to say CAN2.0A and CAN2.0B,CAN2.0A It only supports standard frames , and CAN2.0B It supports extended frames . In common use CAN Take data frame as an example , The standard frame structure is as follows ：

  Total standard frames 127bits, The identifiers in the arbitration domain are 11bits, this 11 Bit identifiers are used not only as priorities but also as message differentiation , But this 11 Bit identifiers limit the maximum number of nodes in the same network , To expand the largest communication node , So there is the extended frame ：

The expansion frame is mainly increased 18 Extended identifier of bit , Therefore, the identifier of the extended frame reaches 29bits, The total length of the frame is 150bits.

3、 ... and 、SAE J1939

SAE J1939 With CAN2.0B Based on , adopt CAN Bus for data communication , Its data link layer defines the data structure of the information frame 、 Encoding rules 、 Including communication priority 、 transport 、 Communication requirements 、 Bus arbitration, etc , Responsible for 29 Bit identifiers for regrouping definitions , Enable the message identifier to describe all the characteristics of the message , Including target address and source address . stay SAE J1939 The most important part of is the protocol data unit （PDU）, It defines a framework to organize data frames ,PDU The composition of the is as follows ：

P： priority , The highest level is 0

R： Keep a , Default 0

DP： Data pages

PF： Group numbered fields （PGN）

PS： Destination address

SA： source address

DataField： data

For source address and destination address , stay J1939 There is a definite definition in , This also means that this set of agreements is a proprietary agreement , In fact, this agreement is usually used for trucks . Now let's simply list some defined addresses ：

• 0x00 For engine controller ;

• 0x0B For the brake system controller ;

• 0x13 For the steering controller ;

• 0x18 For dash cam ;

• 0x33 For tire pressure controller ;

• 0xFF For the whole （ That is, all nodes ）;

Four 、STM32 CAN

STM32 Integrated CAN controller , Controller support CAN2.0A And CAN2.0B, So in use STM32f103 Minimum system development board CAN Communication time , Just put it outside CAN Transceiver is ok , The CAN Transceiver is TJA1050, The line connections are as follows ：

 STM32 There are corresponding CAN library , Need to declare reference ：

  And then there was GPIO Port configuration ：

And then there was NVIC To configure ,CAN The reception of is using USB Interrupt to achieve , So you need to configure NVIC Interrupt priority ：

  And then there was CAN Configuration of ：

  You can see CAN_Filter Both high and low positions of are set 0, Indicates no filtering , In this way, it will receive all messages . If a filter is used, the configuration is as follows ：

  The filter has two modes ： Masks and lists . seeing the name of a thing one thinks of its function , Mask mode can filter single or one segment ID, The list mode can only filter the , Filter details are as follows ：

  The mask setting process is as follows ：

 CAN Sending function of Library ：

 CAN The receiving function of the Library ：

  Usually put the receiving function into the interrupt function ：

No data has been received during the first test , The reason is that I forgot to write USB Interrupt function .

5、 ... and 、 Connect

because CAN Communication is the communication between nodes , Therefore, if you want to view the sent message, you need to transfer the protocol and interface , At present, what is more commonly used is CAN box , You can directly CAN Message through USB Output to PC, But this time STM32 Development board , You can directly put CAN Message through USART Output to PC, The control schematic diagram is as follows ：

Connect the actual picture ：

The stepper motor part is directly applied to what was done before PWM Control motor .

6、 ... and 、 test

CAN The data field is the largest 64bits, That's the most 8Bytes data , Therefore, the data structure defined this time is that the first four digits are the speed setting value of the stepping motor , The last four digits are the set value of the stepper motor position , for example 02003200 It means that the speed is 200, The position value is 3200, The test video is as follows ：

be based on STM32 Of CAN Communication test ： Let the globe turn

The stepper motor driver is set to 3200 pulse / turn , Therefore, the position is set to 3200 Then turn around , The position is set to 1600 Then turn half a turn , The test results are also as expected .

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