Introduction To The Canopen Communication; Can; Data Frame; Remote Frame - WEG CFW-11 Communications Manual

1 Introduction to the CANopen Communication

In order to operate the CFW-11 frequency inverter in a CANopen network, it is necessary to know how the
communication is performed. Therefore, this section brings a general description of the CANopen protocol
operation, containing the functions used by the CFW-11. For a detailed description of the protocol, refer to the
CANopen documentation indicated in the previous section.

1.1 CAN

CANopen is a network based on CAN, which means it uses CAN telegrams to exchange data in the network.
CAN is a serial communication protocol that describes the layer 2 services (data link layer)
In this layer are defined the different types of telegrams (frames), the error detection form, the validation and
arbitration of messages.

1.1.1 Data Frame

In a CAN network data is transmitted by means of a data frame. This frame is composed mainly by an 11 bit
arbitration field
identifier field (
Identifier
11 bits

1.1.2 Remote Frame

Besides the data frame, there is also the remote frame (RTR frame). This type of frame does not have data field, only
identifier. It works as a request, so that another network device transmits the desired data frame.

1.1.3 Access to the Network

In a CAN network any element may try to transmit a telegram in a certain instant. If two elements try to access the
network simultaneously, the one that sends the message with the highest priority will be able to transmit. The
message priority is defined by the CAN frame identifier, the less the value of that identifier, the higher the message
priority. The telegram with an identifier 0(zero) is the one with the highest priority.

1.1.4 Error Control

The CAN specification defines several error control mechanisms, which makes it a very reliable network and with a
very low rate of undetected transmission errors. Each device in the network must be able to identify the occurrence
of those errors and to inform the other elements that an error was detected.
A CAN network device has internal counters that are incremented every time a transmission or reception error is
detected, and decremented when a telegram is sent or received with success. If a considerable amount of errors
occurs, the device can be taken to the following conditions:
Warning
: when this counter exceeds a certain limit, the device enters the
occurrence of a high error rate.
Error Passive
: when this value exceeds a higher limit, the device enters the
acting in the network when detecting that another device sent a telegram with error.
Bus Off
: to conclude, there is the

1.1.5 CAN and CANopen

Only the definitions on how to detect errors and to create and transmit a frame, are not sufficient to define a
meaning for the data that is sent through the network. There must be a specification that indicates how the identifier
and the data must be assembled and how the information must be exchanged. In this way the elements of the
1 In the CAN protocol specification the ISO 11898 standard is referred as the definition of the layer 1 (physical layer) of this model.
2 The CAN 2.0 specification defines two types of data frames:
only standard frames are accepted.
data field
), and a that may contain up to 8 data bytes.
byte 0 byte 1 byte 2
bus off
state, in which the device will no longer send or receive telegrams.
standard
8 data bytes
byte 3 byte 4 byte 5
extended
(11 bits) and (29 bits). For the CFW-11 CANopen protocol,
1 of the ISO/OSI model.
byte 6 byte 7
warning
state, meaning the
error passive
state, then it stops
2