Message frame

A CAN bus message is given a special bit sequence at the beginning and the end. One can say that the message is "framed". A message which is transmitted over a bus is then called a message frame. In the technical literature this is simply called  "frame" .

Here is a distinction between four types of message frames:

• The data frame A CAN station uses data frames if it transmits information over the bus line to another station. This frame type is used most frequently; therefore, in the following chapter, the design of the message frames will use the example of a data frame. Depending on the number of the identifier, a data frame takes either
• the standard format or
• the extended  format.
• The remote frame If one station needs data from another station, it can request it. Most importantly this type of remote frame contains the identifier of the desired information.
• The error frame As soon as a CAN station detects an error in the bus line, it sends an error frame. This alerts all the other stations that the relevant message has an error. The transmitting station now repeats its transmission.

The overload frame If a CAN station detects that the bus is overloaded (i.e. too much data traffic is travelling on the bus line), it sends an overload frame. This orders all the other stations to stop transmission for a short time and then to repeat transmitting.