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SDO download examples


The Initiate SDO Download – Request

The download request is a request to write to a specific Object Dictionary entry. The client (typically the master/configuration tool) sends this request to a SDO server (CANOPEN slave) by using the CAN identifier 600h plus the Node ID of the CANOPEN slave addressed.




Message contents:
  • ccs: Client Command Specifier = 1
  • e: set to 1 for expedited transfer (data is in bytes 4-7)
  • s: set to 1 if data size is indicated
  • n: if e=s=1, number of data bytes in Byte 4..7 that do not contain data
  • x: reserved
  • The Multiplexor contains the Index and Subindex of the OD entry this write access should go to

The Initiate SDO Download – Response

The response sent back from the SDO server to the client indicating that the previously received download (write) request was processed successfully is shown below. The default CAN identifier used for this message is 580h plus the Node ID of the node implementing the SDO server.




Message contents:
  • scs: Server Command Specifier = 3
  • x: reserved
  • The Multiplexor contains the Index and Subindex of the OD entry that received the write access

The Download SDO Segment – Request

If in the initiation sequence a segmented transfer was negotiated, this message is used to transmit the next segment (of up to 7 bytes) from client to SDO server.




Message contents:
  • ccs: Client Command Specifier = 0
  • c: set to 1 if this is the last segment/fragment
  • n: number of data bytes in Byte 1..7 that do not contain data
  • t: toggle bit – set to 0 in first segment, toggled with each subsequent request

The Download SDO Segment – Response

This is the response sent back from the SDO server to the client indicating that the previously received download (write) segment request was processed successfully.




Message contents:
  • scs: Server Command Specifier = 1
  • x: reserved
  • t: toggle bit – set to 0 in first segment response, toggled with each subsequent response