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significant section (as in standard CAN frame) and an 18-bit most significant section,
ensures that the Identifier Extension bit (IDE) can remain at the same bit position in both
standard and extended frames.
In the Extended CAN Data Frame, the SOF bit is followed by the 32-bit Arbitration Field.
The first 11 bits are the least significant bits of the 29-bit Identifier ("Base-ID"). These
11 bits are followed by the recessive Substitute Remote Request (SRR) bit. The SRR is
further followed by the recessive IDE bit, which indicates the frame to be an Extended
CAN frame. If arbitration remains unresolved after transmission of the first 11 bits of the
identifier, and if one of the nodes involved in arbitration is sending a Standard CAN
frame, then the Standard CAN frame will win arbitration due to the assertion of its
dominant IDE bit. Therefore, the SRR bit in an Extended CAN frame is recessive to allow
the assertion of a dominant RTR bit by a node that is sending a Standard CAN Remote
Frame. The SRR and IDE bits are followed by the remaining 18 bits of the extended
identifier and the RTR bit.
Control field and frame termination is identical to the Standard Data Frame.
20.1.2.2 Remote Frames
Normally, data transmission is performed on an autonomous basis with the data source
node (e.g. a sensor) sending out a Data Frame. It is also possible, however, for a
destination node (or nodes) to request the data from the source. For this purpose, the
destination node sends a Remote Frame with an identifier that matches the identifier of
the required Data Frame. The appropriate data source node will then send a Data Frame
as a response to this remote request.
There are 2 differences between a Remote Frame and a Data Frame.
•
The RTR bit is in the recessive state in a Remote Frame.
•
There is no Data Field in a Remote Frame.
If a Data Frame and a Remote Frame with the same identifier are transmitted at the
same time, the Data Frame wins arbitration due to the dominant RTR bit following the
identifier. In this way, the node that transmitted the Remote Frame receives the
requested data immediately. The format of a Standard and Extended Remote Frames is
shown in
Figure
20-2.
User's Manual
MultiCAN, V2.24
Controller Area Network Controller (MultiCAN)
20-5
TC1728
V1.0, 2011-12
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