Omron C200HW-CORT21-V1, Operation Manual

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Communication
Section 1-3
10
1-3-2 Service Data Objects (SDOs)
Purpose of SDO
An SDO defines a message frame, transmitted or received via the CANopen
network. Its main purpose is to configure a CANopen device, or to check its
status. An SDO can address any object within a CANopen device. The SDO
communication is described by the client / server model.
Each SDO is defined by one record in the Communication Profile Area:
•
SDO Parameters
The SDO parameters contain the transmit- and receive communication
identifier (COB-ID) and the node ID of the node to which it is communicating.
Max. SDOs
The maximum number of SDO channels in a CANopen network is 256. It is
mandatory for every CANopen node to have at least one server SDO to
enable initial configuration of the node.
The data field (max. 8 bytes) in a message frame of the first SDO always has
the following format:
The command specifier in an SDO indicates whether it concerns
•
a download or an upload,
•
a request or a response,
•
a segmented-, block- or expedited transfer,
and it contains
•
the number of data bytes in the current frame,
•
the end indicator and
•
an alternating toggle bit for each subsequent segment.
The 3 byte 'multiplexor' is a pointer to the object in the object dictionary.
The remaining bytes carry the parameter data. If the data fits in these
remaining four bytes, it is called an expedited transfer. A single SDO access
to the respective object is sufficient.
If more data needs to be transferred, the data is fragmented into several
segments. The first SDO transmission initiates the down- or upload, and the
following transmissions contain the remaining data. In case of errors, either
the client or the server can abort the transfer. The transfer is completed with
a special SDO, to indicate the end of the transmission.
The SDOs following the first initiating SDO have the format shown in the
figure below. Each message contains 7 bytes of data.