While the second command would result in any frame that starts with a 0x1XX to pass the filter mask. That is because we specified a very strict filter mask of 0x7FF (in binary: 0b 111:1111:1111). The first command will show only the frame with ArbID = 0x123. To filter with candump try the following: Filtering is a simple way to allow you to see only certain frame ArbIDs. The candump command shows messages in a sequence order. Part of the problem you will see with candump is that the messages run very fast, so fast that you don’t have time to see what is going on. If you want a more in-depth knowledge of the Can bus take a look at this: These messages are proprietary, so we don’t know what they mean… yet! By reverse engineering the data we can understand what the bits and bytes mean. Each network can have as many as 40 controllers. Normal Mode messages are the data exchanged normally between controllers. You will start to see that some ArbID’s are the same with the data sometimes changing other times you could have the same ID and different data. CAN Frames cannot exceed 8 bytes of data. This ID is to note the format of the data bytes. The second column tells us what Arbitraion ID (ArbID). We can see the first column tells us what interface we are on. Let’s take a look at the output of the command candump can0 (can0 is our CAN network interface) To receive information we can use open-source tools such as candump or cansniffer. Some times the information will overlap with other networks, but often it does not. Many vehicles will have multiple CAN Buses and each network will have its own messages and information that needs to be shared between controllers. If the vehicle’s controllers are awake, they will transfer information between themselves. That is why it is called Normal Mode Messages. This data is normally there (meaning you don’t have to request it, it just shows up). It is there so controllers can share timely information with each other. That’s why when you connect to a vehicles CAN Bus you’ll see a lot of data, but they’ll be little to no indication on what the data means what the content is in the data bytes. So the data does not need to follow any protocol other than that of the physical layer itself. It is not meant to be routed or shared beyond the vehicle and its controllers (for the most part). The data that goes across the networks is local to the vehicle. Each vehicle’s network is expressly designed by the vehicle’s manufacturer. These controllers are repsonsible for gathering and sharing information about sensors, vehicle states, information, and calibration. Vehicle CAN Buses are networks that connect controllers.
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