5. Access Procedure
Festo P.BE-CMMP-CO-SW-EN 0708NH
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5.
Access Procedure
5.1
Introduction
CANopen provides a simple and standardised possibility to access the parameters of the
motor controller (e.g. the maximum motor current). To achieve this, a unique number
(index and subindex) is assigned to each parameter (CAN object). The totality of all
adjustable parameters is designated an object directory.
Essentially two methods are available for accessing CAN objects via the CAN bus:
A confirmed access type, in which the motor controller acknowledges each parameter
access (via so-called SDOs), and an unconfirmed access type, in which no
acknowledgement is made (via so-called PDOs).
Control
unit
CMMP
Access form control unit
Acknowledge from
motor controller
SDO
Control
unit
CMMP
Confirmation from
motor controller
PDO
(Transmit-PDO)
Control
unit
CMMP
Process data from
control unit
PDO
(Receive- PDO)
Fig. 5.1: Access Procedure
As a rule, the motor controller is parameterised and also controlled via SDO access. In
addition, other types of messages (so-called communication objects), which are sent
either by the motor controller or the higher-level controller, are defined for special
application cases:
SDO
S
ervice
D
ata
O
bject
Are used for normal parameter setting of the
motor controller.
PDO
P
rocess
D
ata
O
bject
Fast exchange of process data
(e.g. actual speed) possible.
SYNC
Sync
hronisation
message
Synchronisation of multiple CAN nodes
EMCY
Em
ergen
cy
message
Transmission of error messages.
NMT
N
etwork
M
anagemen
t
Network service: All CAN nodes can be worked on
simultaneously, for example.
HEARTBEAT
Error Control Protocol
Monitoring of the communications participants
through regular messages.
Every message sent on the CAN bus contains a type of address which is used to determine
the bus participant for which the message is meant. This number is designated the
identifier.
Summary of Contents for CMMP Series
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