Argo-Hytos OPCom - 16.1.3 Service Data Object (SDO)

Subject to change · V 2.02.20 · EN
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Depending on the sensor state, various services of the CANopen protocol are available:
Com. Object Initializing Pre-Operational Operational Stopped
PDO X
SDO X X
Synch X X
BootUp X
NMT X X X
16.1.3 Service Data Object (SDO)
Service Data Objects provide read and write access to the sensor's object dictionary. The SDOs are acknowledged; transfer is always
performed between only two participants, a so-called client / server model.
The sensor can only function as a server, it only responds to SDO messages and does not spontaneously send any queries to other
participants The ID of the SDO messages from the sensor to the client is NodeID+0x580. The expected ID for requests from the client
to the sensor (server) in the case of SDO messages is NodeID+0x600.
The standard protocol for SDO transfer requires 4 bytes in order to encode the sender direction, data type, index and sub-index. Thus
4 bytes remain of the 8 bytes of a CAN data field for the data content. For objects whose data content is greater than 4 bytes, there
are two additional protocols for the so-called fragmented or segmented SDO transfer.
SDO Client (Controller)
CAN
ID
Message
ID
Message
SDO Server (Sensor)


Table 27: Available CANopen services in various sensor states
Table 28: Setup of a SDO message
Fig. 27: SDO Client / Server relationship
SDOs are intended to configure the sensor via access to the object dictionary, to inquire seldom needed data or configuration values,
or to download large data volumes. The SDO features at a glance:
› Access to all data in the object dictionary
› Confirmed transfer
› Client / Server relationship when communicating
The control and user data of a non-segmented SDO standard message is distributed across the CAN message as shown in the
following table. The user data in an SDO message usually consists of up to 4 bytes. The control data in an SDO message (Cmd,
index, sub-index) is used to determine the direction of access to the object dictionary and the transferred data type if applicable.
Please consult "CiA Draft Standard 301" for the exact specifications of the SDO protocol.
CAN CAN-ID DLC
CAN Message user data
0 1 2 3 4 5 6 7
CANopen
SDO
COB-ID 11 Bit DLC Cmd Index Sub-index CANopen SDO Message user data