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CANOpen
CanOpen is a protocol originally designed on top of the CAN bus to provide a more efficient abstraction over raw CAN.
It servers a somewhat similar purpose to TCP/UDP on top of IP, providing a standardized (and mostly manufacturer independent) mechanism for data exchange between devices including segmentation for data that would exceed the length of a single CAN message (of 8 bytes).
Terminology
| Term | Description |
| Node | Device on the network that sends and/or receives messages |
| Node ID | unique numerical identifier for a given node (each node must have one) |
| Object | A property („thing“) of a node, such as a sensory value, motor target speed or configuration data |
| Index | 16 bit number that identifies an object |
| Sub-Index | 8 bit number allowing access an object's elements (for structured data or arrays |
| Object Dictionary | a dictionary containing information for all the objects a given node supports, including its CanOpen configuration |
| PDO | „Process Data Object“, PDOs allow efficient transfer of multiple objects in a signle CAN message. CanOpen allows for a maximum of 512 PDOs per Node, however most devices will limit it to 4 (more info, see below) |
| SDO | „Service Data Object“: provides mechanism to access a node's entire object dictionary. (more info, see below) |