The arbitration field of the CAN message consists of an 11- or 29-bit identifier and a remote transmission (RTR) bit. ... The RTR bit simply distinguishes between data frames and remote frames. In data frames, the RTR bit must be dominant; in remote frames it must be recessive.

What is RTR in CAN frame?

RTR is used for remote request frames. It is a feature that allows you to send an empty package, requesting data of the same identifier as you used for the RTR frame. This feature has nothing to do with identifier lengths in itself.

CAN bus message structure?

A message or Frame consists primarily of the ID (identifier), which represents the priority of the message, and up to eight data bytes. A CRC, acknowledge slot [ACK] and other overhead are also part of the message. The improved CAN FD extends the length of the data section to up to 64 bytes per frame.