Sdo Access - Festo CiA 402 Manual

3 CANopen access procedure
Communication objects
SDO Service Data Object
PDO Process Data Object
SYNC Synchronisation Message
EMCY Emergency Message
NMT Network Management
HEART- Error Control Protocol
BEAT
Tab. 3.1 Communication objects
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 and from which bus participant the message is sent. This
number is designated the identifier. The lower the identifier, the higher the priority of the message.
Identifiers are established for the above-named communication objects
sketch shows the basic design of a CANopen message:
Identifier Number of data bytes (here 8)
601 Len
h
3.2

SDO access

The Service Data Objects (SDO) permit access to the object directory of the motor controller. It is there-
fore recommended to build up an application, without prepared PDO communication from the control
interface, at first only with SDOs and only later to convert to the faster but also more complicated Pro-
cess Data Objects (PDOs).
SDO access always starts from the higher-order controller (Host). This either sends the motor control-
ler a write command to modify a parameter in the object directory, or a read command to read out a
parameter. For each command, the host receives an answer that either contains the read-out value or –
in the case of a write command – serves as an acknowledgement.
For the motor controller to recognise that the command is meant for it, the host must send the com-
mand with a specific identifier. This consists of the base 600
volved. The motor controller answers correspondingly with the identifier 580
The design of the commands or answers depends on the data type of the object to be read or written,
since either 1, 2 or 4 data bytes must be sent or received. The following data types are supported:
18
Used for normal parameterisation of the motor controller.
Fast exchange of process data (e.g. actual speed) possible.
Synchronisation of multiple CAN nodes.
Transmission of error messages.
Network service: All CAN nodes can be worked on
simultaneously, for example.
Monitoring of the communications participants through
regular messages.
Data bytes 0 ... 7
D0 D1 D2 D3
Festo – GDCP-CMMS/D-C-CO-EN – 1404NH – English
Section 3.7. The following
D4 D5 D6 D7
+ node ID of the motor controller in-
h
+ node ID.
h