The following will address data and remote frames and how they, consequently, are distinguished from each other.
Both, Data Frame and Remote Frame, are very similar. Basically, the Remote Frame is a Data Frame without the Data Field.
Per definition a CAN data or remote frame has the following components:
- SOF (Start of Frame) – Marks the beginning of data and remote Frames
- Arbitration Field – Includes the message ID and RTR (Remote Transmission Request) bit, which distinguishes data and remote frames
- Control Field – Used to determine data size and message ID length
- Data Field – The actual data (Applies only to a data frame, not a remote frame)
- CRC Field – Checksum
- EOF (End of Frame) – Marks the end of data and remote frames
Picture 4.2.2 shows the CAN frame in more detail.
Each CAN message starts with a “Start of Frame” bit (SOF), followed by the message identifier and the “Remote Transmission Request” bit (RTR). This particular bit, the RTR bit, is now the focus in explaining the difference between a Data Frame and a Remote Frame, which are both very similar. A more detailed explanation of the CAN message frame will follow in Chapter 4.5 – Message Frame Format.