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SDO (Service Data Object)

The SDO protocol is used for direct access to a device's Object Dictionary (OD). It supports reading (Upload) and writing (Download) of values. All CiA 301 SDO transfer modes are supported:

  • Expedited transfers
  • Segmented transfers
  • Block transfers

SDO Client (Accessing Remote Nodes)

To communicate with another node on the network (acting as an SDO Client), you typically use a RemoteNode or the Network raw API.

Using RemoteNode

If you have a RemoteNode instance (e.g., from network.AddRemoteNode), you can use its helper methods to read entries.

// Create a remote node, with id 6 and load the object dictionary from given file
node := network.AddRemoteNode(6, "/path/to/object_dictionary.eds")

// Read a value (Index 0x2001, SubIndex 0)
data, err := node.Read(0x2001, 0)
if err != nil {
    // Handle SDO Abort or Timeout
    log.Printf("SDO Read failed: %v", err)
}

Using Network Raw API

You can also send SDO requests directly via the Network object without explicitly managing a RemoteNode.

// Read Raw: Node 0x10, Index 0x2000, SubIndex 0
buffer := make([]byte, 8)
nbRead, err := network.ReadRaw(0x10, 0x2000, 0, buffer)

// Write Raw: Node 0x10, Index 0x2000, SubIndex 0
value := uint16(600)
// false = disable block transfer (use expedited/segmented)
nbWritten, err := network.WriteRaw(0x10, 0x2000, 0, value, false)

SDO Server (Local Node)

If you are running a LocalNode, it automatically acts as an SDO Server. To interact with the Local Node's OD (which is what SDO clients access), see the Local Node Documentation.