11.2.3.2 Acceptance Filter
Each receive buffer has its own acceptance filter that is used to filter incoming messages. An acceptance filter consists of Acceptance Mask Register (AMR) and Acceptance Code Register (ACR) pair. The AMR defines which bits of the incoming CAN message match the corresponding ACR bits.
The following message fields are covered:
- ID
- IDE
- RTR
- Data byte 1 and data byte 2
Important: Some CAN HLPs such as Smart Distributed System (SDS)
or DeviceNet carry additional protocol related information in the first or first and second
data bytes that are used for message acceptance and selection. Having the capability to
filter these fields provides a more efficient implementation of the protocol stack running
on the Cortex-M3 processor.
The AMR register defines whether the incoming bit is checked against the ACR register. The incoming bit is checked against the respective ACR when the AMR register is 0. The message is not accepted when the incoming bit does not match the respective ACR flag. When the AMR register is 1, the incoming bit is a “don't care”.