Anyone who knows the CAN bus knows that when the frame data of the CAN bus is transmitted on the bus, other CAN controllers determine whether the ID of the data frame on the bus matches the node by acceptance filtering, if it matches the node. Then, the data on the bus is stored in the corresponding register of the bus controller, otherwise the data is discarded, thereby reducing the workload of the bus controller. In other words, the ID of the data frame on the bus is matched by the acceptance filtering of the node to be received, and can be received.
So, how does the bus controller perform acceptance filtering? Acceptance filtering is divided into single filtering and double filtering. Standard and extended frames differ in their two filters due to their different ID lengths. Here I only focus on an example, because as long as you understand a filtering method, other filtering methods are similar, and it is easy to understand.
Here we say the double filtering of the extended frame. The so-called double filtering means that there are two filterings, but not both filterings need to pass through the double pass. Once the filtering is successful once, the filtering is passed by default, and the data can be received. 
As shown in the above table, the ACR register is the receive code register and the AMR is the receive mask register. The ACR generally needs to match the corresponding ID, but if the corresponding bit of the AMR is set to 1, the bit of the ID data may not be the same as the corresponding bit of the AMR, that is, it acts as a mask.
for example. If ACR0=11101111, AMR0=00000000, then to pass the acceptance filtering, ID.28-ID.21=ACR0=11101111 is required. If AMR0=00010000, then ID.28-ID.21=11111111, it can also pass the acceptance filtering, because the fifth bit of AMR0 is 1, that is, the fifth bit of ACR0 is masked. Therefore, the corresponding bit of the ID may not be consistent with ACR0.
In the dual filtering mode of the extended frame, ACR0\ACR1 corresponds to ID.28-ID.13, and ACR2\ACR3 also corresponds to ID.28-ID.13, which achieves the effect of two filterings.
Another point to note is that the data that meets the node requirements after acceptance filtering is stored in the corresponding register of the node, and other frame information is not stored.
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