CAN bus (hardware)

 

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Author: Pony

CAN bus, this is the last part of my design. As of this evening, the hardware has been completed, and 90% of the software has been completed. The PCB Board teacher has already processed it, and it is estimated that it can be written before the board arrives.Code. After welding the board, you can directly debug it. Here, I will write down some experiences in the hardware part, and wait for me for the software part.ProgramAfter successful debugging, I will write another articleArticle.

First, let's briefly introduce my task. One PCB has three can nodes, simulating 485 master-slave communication. One of them is a host, and the other two are slave machines. The slave machine has a stepping motor. The process is that the computer sends a series of commands through the serial port. The lower computer parses the commands into the CAN protocol and controls the motor rotation of the two slave machines through the CAN bus.

At the beginning, I was a little confused, because I have never done can before, and no one has done it in the lab. When I first joined the lab, I could ask my teacher or graduate students in the lab. but now they have never done can, and I have to do it myself. the teacher asked me to do this can because no one in the lab has done it before. All the medical instruments previously developed in the lab use 485 bus. The teacher saw the decline of 485, And the can could be dug up. So I want to switch to can.

In fact, there are not many things on the hardware for my task. the main reason is that the software workload is large. the circuit I designed is a node consisting of the lpc2109 (built-in 1-channel CAN controller) and the ctm1050 (can transceiver. the entire board has three such nodes. In addition, with the serial port connector, the buzzer is used for debugging. two layers of PCB can be done.

The circuit of one node transceiver is as follows:

 

 

Let's take a look at the ctm1050 manual to understand the role of each pin. Here we will talk about two points:

The terminal resistance of 120 euro must be connected. It can filter out the self-oscillation during the connection process.

2. If it is convenient for copper-clad devices, it is best to replace the transceiver with copper separately. I didn't do this on the board. I was thinking that three nodes are on a board and there should be little interference. therefore, there is no copper coating. this suggestion was later called by Zhou ligong and the engineer there gave me the suggestion.

In fact, the hardware part of a can-Based Large system has a lot to do. nowadays, many cars use the CAN bus. there are many experiences and suggestions on hardware when designing a large system like a car, such as the selection of communication cables. I will not talk about it here.