Doc.Id. SCM-1200-121
Anybus Communicator CAN to CANopen
Doc.Rev. 1.00
Chapter 4
4. CAN Network Communication
4.1 General
The CAN protocol is message-based and offers the possibility to exchange up to 8 bytes of data in each
message. How these bytes are interpreted, is defined in each application. The CAN protocol is a trans-
parent protocol, meaning that it only acts as a data carrier, and it is up to the users (the application) to
define and interpret the data content of the messages.
Data on CAN is exchanged using frames. Each frame has a unique identifier for the data it exchanges.
The identifier also represents the message priority on the CAN network. The Anybus Communicator
CAN supports 11-bit (CAN 2.0A) and 29-bit (CAN 2.0B) identifiers.
CAN is essentially a produce-consume network, where all nodes listen to all messages. The devices rec-
ognize what data to collect by what identifier the CAN frame carries. The Communicator is also able to
act as a Master and issue queries that demand responses. It is possible to use both methods in the same
configuration of the module.
4.2 Types of Messages
The Anybus Communicator CAN features three different message types regarding the subnetwork com-
munication, called ‘Query/Response’, ‘Produce’ and ‘Consume’. Note that these messages only specify
the basic communication model, not the actual CAN protocol. All three types of messages can be used
in the same configuration.
4.2.1 Query-Response
The Communicator acts as a master on the subnetwork, and the serial communication takes place in a
query-response fashion. The Communicator sends a query and expects an answer within the specified
timeout.
Subnetwork Devices
Gateway
Control System
