Welcome to the CAN-bus Wiki project

This is an old revision of the document!


Why using RTRs is not advised in CANopen?

RTR means Remote Transmission Request - a CAN frame requesting another node to send a requested frame.

CiA, especially the Special Interest Group CANopen is not recommending using RTR Messages. You may ask: why?

The CiA has a paper explaining the contras and giving advice for better solutions. CiA 802 V1.1.0: CANopen application note - CAN remote frames: Avoiding of usage (IGCO_802v01010000.pdf)
It can be downloaded free of charge after a registration at CiA specifications.

In short the main topics:

  • The number of transmit messages buffers supporting CAN remote frames is limited on most so-called Full CAN controllers.
  • Implementation of a CAN driver handling RTR is much more complex. On some controllers impossible.
  • Some CAN controllers react different on the 'data length' code in the RTR frame and the data frame. This is due to differences in the CAN implementation.

QR Code
QR Code can_higher_layer_protocols:what_is_wrong_with_rtr (generated for current page)