GEMTEQ I/O 2. Introduction to CAN Networks
2. INTRODUCTION
The GEMCAN network is based on the CANopen communication model and uses standard CAN
hardware and cabling.
The CANopen standard consists of an addressing scheme, several small communication
protocols and an application layer defined by a device profile. The communication protocols have
support for network management, device monitoring and communication between nodes.
CAN_H
CAN_L
Gnd
CAN_H
CAN_L
Gnd
CAN_H
CAN_L
Gnd
CAN_H
CAN_L
Gnd
Figure 2-1
Network Cabling between 4 Nodes
2.1
INTRODUCTION TO CAN NETWORKS
Modules on the CAN network must have a unique node address. One node (NMT Master) is
responsible for issuing all the relevant commands to take all the other nodes on the network to an
“operational” state.
Data transfer on a CANopen network is via a Producer and Consumer architecture. Each data
packet has a unique identifier, with each node seperatley configured to define which
packet/packets it will Produce and Consume. This allows a large flexibility in which modules can
talk to each other, but also requires a complex configuration procedure.
There are two types of data packets:
•
PDO (Process Data Objects)
•
PDO have a high priority for system data exchange and can contain up to 8 bytes of data. The
size and number of PDO’s a module will use on the network is variable and described by the
module hardware profile.
SDO have a low priority and are used for module configuration and can contain more than 8
bytes.
GEMTEQ has simplified the configuration of the CAN network with the introduction of a
theoretical master slave architecture.
When a master scanner module is declared on a GEMTEQ system it will not only perform all the
functions of an NMT master .i.e. ensuring all slaves are taken to the operational state, but will
also become the hub of all message transfers. It will produce all of the slaves consumed PDO’s
and consume of all the slaves produced PDO’s. The mapping between data within the GEM80-
500 controller and the slave modules is a simple correlation between the Node address and the
controllers C/D tables see Appendix A.
Note: There is not facility for a slave module to transfer date directly to another slave module.
GEMTEQ I/O Technical Manual (T2031En)
Rev.02 (10/10)
Page 2-1
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