station sends out, the slave station needs to return data response. This communication
method is only suitable for parameter setting, not suitable for data transmission with high
real-time requirements.
The communication mode of SDO is divided into upload and download. The host computer
can read and write the OD inside the servo according to the dedicated SDO read and write
instructions. In the CANopen protocol, the content of the object dictionary can be modified
through SDO (Service Data Object). The structure of the SDO command and the guidelines to
follow are described below.
Basic structure of SDO
:
Client
→
Server/Server
→
Client
The SDO command word contains the following information
:
⚫
Download/upload
⚫
Request/response
⚫
Segmented/expedited transfer
⚫
CAN frame data bit length, used for alternately clearing and setting toggle bits for
each subsequent segment. 5 request/response protocols are implemented in
SDO
:
⚫
nitiate Domain Download
⚫
Download Domain Segment
⚫
Initiate Domain Upload
⚫
Upload Domain Segment
⚫
Abort Domain Transfer
Among them, Download refers to the write operation of the object dictionary, and
Upload refers to the read operation of the object dictionary; when reading parameters, use
the Initiate Domain Upload protocol; when setting parameters, use the Initiate Domain
Download protocol; the SDO command word of the protocol (SDO CAN The first Bit) syntax
of the message is described in Table 10-8 and Table 10-9, where "-" means irrelevant and
should be 0).
Table
10-8
Initiate Domain Download