| 摘要 |
The 29 bit identifier field of a standard CAN protocol message format is subdivided into a message function portion, a class one node identifier portion, to identify class one nodes which must be able to communicate with each other as well as with a large number of other nodes in the system, and a selectable node identifier portion, the vast majority of which is utilized for class two node identifiers, to identify class two nodes which never need to communicate with each other, but only need to communicate with class one nodes, and a small portion of which is utilized for class one node identifiers for cases where two class one nodes are communicating with each other. The least significant eight bits of the selectable portion represent class one identifiers when the most significant eight bits of the selectable portion are all zeros, but when any of the most significant eight bits of the selectable portion represents a one, then the lowest ordered eight bits are part of a class two identifier. Thus, the selectable portion can identify, for example, 256 class one nodes and 65,280 class two nodes.
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