Canopen Network Characteristics; Physical Medium; Address In The Canopen Network; Access To The Data - WEG CFW-11 Communications Manual

network can interpret correctly the transmitted data. In this sense, the CANopen specification defines exactly how to
exchange data among the equipments, and how each device must interpret these data.
There are several other protocols based on CAN, as DeviceNet, J1939, etc., which also use CAN frames for the
communication. Those protocols however cannot co-operate in the same network.

1.2 CANopen Network Characteristics

Because of using a CAN bus as telegram transmission means, all the CANopen network devices have the same
right to access the network, where the identifier priority is responsible for solving conflict problems when
simultaneous access occurs. This brings the benefit of making direct communication between slaves of the network
possible, besides the fact that data can be made available in a more optimized manner without the need of a
master that controls all the communication performing cyclic access to all the network devices for data updating.
Another important characteristic is the use of the producer/consumer model for data transmission. This means that
a message that transits in the network does not have a fixed network address as a destination. This message has an
identifier that indicates what data it is transporting. Any element of the network that needs to use that information
for its operation logic will be able to consume it, therefore, one message can be used by several network elements
at the same time.

1.3 Physical Medium

The physical medium for signal transmission in a CANopen network is specified by the ISO 11898 standard. It
defines as transmission bus a pair of twisted wires with differential electrical signal.
The CFW-11 frequency inverter uses an interface isolated from the network. The power supply for the CANopen
interface is shared with the digital and analog inputs and outputs present on the CFW-11 control board. The
component responsible for the transmission and reception of the signals is denominated transceiver, which complies
with the specified by the ISO 11898.

1.4 Address in the CANopen Network

Every CANopen network must have a master responsible for network management services, and it can also have a
set of up to 127 slaves. Each network device can also be called node. Each slave is identified in a CANopen
network by its address or Node-ID, which must be unique for each slave and may range from 1 to 127.
The CFW-11 does not have functions for implementing the network management services; therefore, it must be
used together with some equipment that has such services, generally a CANopen network master.

1.5 Access to the Data

Each slave of the CANopen network has a list called object dictionary that contains all the data accessible via
network. Each object of this list is identified with an index, which is used during the equipment configuration as well
as during message exchanges. This index is used to identify the object being transmitted.
A more detailed description on how the dictionary is structured is presented on section 6.

1.6 Data Transmission

The transmission of numerical data via CANopen telegrams is done using a hexadecimal representation of the
number, and sending the least significant data byte first.
E.g.: The transmission of a 32 bit integer with sign (12345678h = 305419896 decimal), plus a 16 bit integer with
sign (FF00h = -256 decimal), in a CAN frame.
Identifier 6 data bytes
32 bit integer 16 bit integer
11 bits
byte 0 byte 1 byte 2 byte 3 byte 4 byte 5
78h 56h 34h 12h 00h FFh