User Manual of EL6-CAN AC Servo
www.leadshine.com
55
Chapter 5 CANopen
5.1 CAN Interface
The CAN-bus
(
Controller Area Network-Bus
)
is a serial communication protocol developed by Bosch to
exchange information between electronic control units on automobiles. This system makes possible to share a
great amount of information between nodes and control units appended to the system, leading to a major
reduction in both the number of sensors required and the quality of cables in the electrical installation.
The CANopen protocol is based in CAN specification, and its frame definition is such that one CAN frame is
required for each CANopen message.
5.2 CANopen protocol
CANopen is the internationally standardized CAN-based higher-layer protocol for embedded control system ,
as developed and maintained by CiA members. The set of CANopen specifications comprise the application
layer and communication profile, as well as application, device, and interface profiles. CANopen provides very
flexible configuration capabilities, and for this reason CANopen networks are used in a very broad range of
application fields, such as machine control, medical devices, off-road and rail vehicles, maritime electronics,
building automation, power generation, etc.
The CANopen protocol defines basically two aspects of the communication protocol: how the communication
should be formatted
(
CANopen frame
)
,and what objects are defined in common. Those objects may be used to
configure or arbitrate the communication, or simply to exchange application data. Communication objects are
available to:
Exchange process and service data.
Process or system time synchronization.
Error state supervision.
Control and monitoring of node states.
EL6-CAN series follow the communication rules:
Comply with CAN 2.0A standard
Comply with CANopen standard protocol DS 301 _V4.02
Comply with CANopen standard protocol DSP 402 _V2.01
5.2.1 CANopen frame
CANopen protocol is based in CAN frames and uses one CAN frame for each CANopen message. There are
two important parts of the frame that the user needs to modify: the arbitration field and the data field. The rest
of the fields of the frame are normally automatically configured by the CAN hardware.
Arbitration field
In CANopen messages the identifier part of the arbitration field is known as Communication Object Identifier
(
COB-ID
)
. It is divided into a 4-bit part function code and a 7-bit node-ID as depicted::
Bit number:
10
9
8
7
6
5
4
3
2
1
0
Identifier
(
COB-ID
)
Function code
Node-ID