Normally, data transmission is performed on an
autonomous basis by the data source node (e.g., a
sensor sending out a data frame). It is possible,
however, for a destination node to request data from
the source. To accomplish this, 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 in response to the remote frame request.
There are two differences between a remote frame
(shown in Figure 2-3) and a data frame. First, the RTR
bit is at the recessive state and, second, there is no
data field. In the event of a data frame and a remote
frame with the same identifier being 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 desired data immediately.
http://ww1.microchip.com/downloads/en/DeviceDoc/21801d.pdf
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