ElmoMC CANopen DS 301 Implementation Guide - Manual (Page 10)

Chapter 2: CANopen Basics
This chapter describes — in general — the CANopen communication features most
relevant to Elmo
SimplIQ servo drive. More detailed information is available in the
specific CANopen documentation.
2.1 Physical Layer
CAN is a serial communication standard in which the transferred data is coded as
electrical pulses on a two-wire communication line. The device that handles the CAN
physical layer is called the CAN controller. The device that transmits data over the CAN
lines is called the CAN transceiver. SimplIQ digital servo drives use a CAN controller built
into the drive DSP.
2.2 Standard vs. Extended Addressing
Each CAN message frame includes an arbitration field that defines the type of data sent
and its address. CAN version 2.0A supports 11 arbitration bits for this purpose; the seven
least significant define the address and the four most significant define the type of
message sent. Only 16 message types are supported. CAN version 2.0B supports 29
arbitration bits, of which the seven least significant define the address and 21 bits define
the message type. In CiA DS 301, the arbitration bits indicate the object and the node-ID,
together comprising the COB-ID.
CAN communication is prioritized so that messages with higher priority are transmitted
first. The arbitration field determines the message priority: The lower the number in the
arbitration field, the higher the message priority. ID 0 gives the highest priority. The
SimplIQ drives support the CAN version 2.0A (11-bit) addressing method only, meaning
that it ignores messages of 29 bits. A setup parameter (PP[13] - Node ID) selects the CAN
object identification to be used.
2.3 Client - Server Relations
A CAN master (or client) is a controller that makes requests to nodes to respond to its
commands. A CAN slave (or server) responds to the commands issued by the CAN
master. The CAN protocol permits both single-master and multiple-master networks.
The SimplIQ servo drives assume a single-master network arrangement, in which the
servo drives are the slaves and the machine controller or PLC is the master. Every servo
drive has a unique ID in the range [1…127]. The network master does not require an ID.
As a slave, the servo drive never sends an unrequested message, other than emergencies.
The drive responds only to messages addressed to its ID or to broadcast messages, which
have an ID of 0. All messages sent by a servo drive are marked with its own ID.
If two servo drives have been assigned the same ID, the CAN network may crash.
CANopen DS 301 Implementation Guide CANopen Basics
MAN-CAN301IG (Ver. 2.1)
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