Hongke share | let you have a comprehensive understanding of "can bus error" (III) -- can node status and error counter

In this series of articles , We will give you a detailed introduction to CAN Knowledge about bus errors , Include CAN The basic concept of bus error 、CAN Type of bus error 、CAN Error frame and CAN Node error status , And generate and record through the actual application test CAN error .

Previous review ：
1. CAN Bus errors and error frames
2. CAN Wrong type

obviously ,CAN Error handling helps remove error messages , And make CAN The node can retransmit the error message . This ensures short-term local interference （ For example, from noise ） Will not result in invalidity / Lost data . contrary , The sender will try to resend the message . If it wins the arbitration （ And there are no mistakes ）, The message is sent successfully .

however , What if the error is caused by a system failure in the transmission node ？ This may trigger sending / Remove the infinite loop of the same message —— interfere CAN Bus . This is it. CAN Where node status and error counters work .

In short ,CAN The purpose of error tracking is to reduce the problem CAN Node permissions to limit errors . say concretely , Let's look at three possible states ：

• Error activity ： This is every CAN The default state of the node , In this state, it can transmit data and cause “ Active error flag ”
• Passive error ： In this state ,CAN Nodes can still transmit data , But now when an error is detected “ Passive error flag ”. Besides ,CAN Nodes now have to wait 3 Bit interrupt time out , You have to wait for additional 8 position （ Also known as pause transmission time ） To resume data transmission （ To allow others to CAN Node control bus ）
• Bus off ： In this state ,CAN The node associates itself with CAN The bus is disconnected , No more data can be transmitted or an error flag is raised
  
  Every CAN The controller will track its status and take corresponding actions .CAN The node transitions state according to the value of its error counter . say concretely , Every CAN The node will track the send error counter (TEC) And receive error counter (REC)：
• If REC or TEC exceed 127, be CAN Nodes enter ErrorPassive state
• If TEC exceed 255, be CAN The node enters the bus off state

So how does the error counter change ？ Before we learn how to increase / Before reducing the logic of the error counter , Let's re-examine CAN Error frames and main / Minor error flags .

from CAN The error frame diagram can be clearly seen , stay CAN Wrong frame 6 Dominant sequences were followed by CAN The node will know that it raises the main error flag . under these circumstances , We can put this CAN Nodes are called wrong “ Discoverer ”.

At first , To make a CAN Nodes repeatedly find errors and react quickly by sending error flags in front of other nodes , This may sound positive . However , In practice , Discoverers are often the culprits of mistakes .

in application , It is usually possible to use CAN The recorder is right CAN Errors are recorded , And through the CAN Analyze the data to find the cause of the failure , For example, use Hongke CAN The recorder can easily transfer data from 2xCAN/LIN The bus records 8-32GB Of SD In the card , Or through WiFi Automatically transfer data to the server , So just connect it to a car or truck to start recording , And through free software /API Decode data .

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