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5.6
Service Data Objects (SDO)
The Service Data Objects (SDO) form the communication channel for the transmission
of device parameters (e.g. programming the encoder resolution) and are used for status
requests.
Data of any length can be transmitted using SDOs. The data may need to be divided
between several CAN messages. An SDO is always transmitted with confirmation, i.e.
the reception of each message is acknowledged by the receiver.
Transmit SDO and Receive SDO
The AHS/AHM36 CANopen and AHS/AHM36 CANopen Inox has one Transmit SDO
channel and one Receive SDO channel to which two CAN identifiers are assigned.
The SDO communication is compliant with the clientserver model. In this process the
encoder represents an SDO server.
The SDO client (e.g. the PLC) specifies in its request the parameter, the access type
(read/write) and, if necessary, the value. The encoder undertakes the write or read
access and responds to the request.
The data area of a CAN telegram, maximum 8 bytes long, is configured by an SDO as
follows:
Table 28: Format of the SDO
COB-ID
CCD
Index
Subin‐
dex
Data
600h +
Node-ID
Byte 0
Byte 1
Byte 2
Byte 3
Byte 4
Byte 5
Byte 6
Byte 7
The Command Code (CCD) identifies whether data are to be read or written. In the case
of an error, the data area contains a 4byte error code that provides information on the
origin of the error
see "Error during the SDO transfer", page 91
.
Figure 11: Example for Transmit SDO and Receive SDO
INTEGRATION IN CANOPEN
5
8016869/1EF3/2021-12-08 | SICK
O P E R A T I N G I N S T R U C T I O N S | AHS/AHM36 CANopen
AHS/AHM36 CANopen Inox
29
Subject to change without notice