CANopen & CANlink Communication
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4 CANopen & CANlink Communication
4.1 Introduction
The CANopen communication protocol is an international standard protocol. The
CANlink communication protocol is a dedicated protocol independently developed by
Inovance based on CAN bus application. This protocol can be used for
communication with only Inovance PLCs such as H2U, H3U, and AM600.
Communication Model
CANopen is an application layer protocol of network transmission system based on
the CAN serial bus. The CAN bus follows an ISO/OSI standard model. This protocol
defines the data link layer and some physical layers in the OSI model. It allows the
multi‑master mode, in which any node in the network can send a message to other
nodes. Network nodes are assigned with different priorities based on system real‑
time requirements, which can reduce the bus arbitration time in case of a
transmission collision. The CAN network adopts communication data block coding
instead of traditional address coding. With data block coding, the number of nodes in
the network is not limited theoretically, and different nodes can receive the same
data at the same time. This coding mode also features short transmission byte, high
speed, great fault tolerance, and reliable data transmission, making it suitable for
industrial control and distributed real‑time control. The following figure shows a
CANopen equipment model.
Figure 4‑1 CANopen communication model
The following introduces the object dictionary, common communication objects, and
CANopen message format in the CANopen communication model.
Protocol Features
CANopen supports six protocols:
● NodeGuard protocol, which enables the master to query device status
● Heartbeat protocol, which enables the slave to report its current state to the
master regularly
● Accelerated transmission mechanism of Service Data Object (SDO) (one parameter
or one object dictionary is transmitted at a time)
● Four TPDOs and four RPDOs
● Emergency objects
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