CANopen data link layer
CANopen is based on the Classical CAN data link layer, as standardized in ISO 11898-1. All CANopen protocols are transferred via the CAN, by utilizing one or several CAN data frames. By default, CANopen uses the Classical CAN data frame in the base frame format (CBFF). Nevertheless, CANopen supports the extended frame format as well. Additionally, e.g. to realize migration paths, CANopen can be mapped to a CAN FD data link layer. Remember, CANopen devices using different data link layer implementations are not interoperable any longer. Additionally, a classic CANopen stack running on a CAN FD data link layer, would limit the maximum usable payload to 8 Byte of data. In case the full performance of CAN FD shall be used, we recommend the usage of CANopen FD, which is optimized for the use on a CAN FD data link layer.
CANopen bit timing
The table below illustrates the CANopen bit timing, the resulting maximum network length, and the maximum unterminated cable drop lengths. All CANopen devices shall support at least one of the given bit rates. Optionally, a CANopen device may support further bit rates. The location of the sample point shall be as close as possible to 87,5 % of the bit time.
CANopen bit timing table
| Bit-Rate | Bus length | Max. stub length | Accumulated stub length |
|---|---|---|---|
| 1 Mbit/s | 25 m | 1,5 m | 7,5 m |
| 800 kbit/s | 50 m | 2,5 m | 12,5 m |
| 500 kbit/s | 100 m | 5,5 m | 27,5 m |
| 250 kbit/s | 250 m | 11 m | 55 m |
| 125 kbit/s | 500 m | 22 m | 110 m |
| 50 kbit/s | 1000 m | 55 m | 275 m |
| 20 kbit/s | 2500 m | 137,5 m | 687,5 m |
| 10 kbit/s | 5000 m | 275 m | 1375 m |
CANopen physical layer
CANopen assumes a physical layer according to ISO 11898-2. The “CANopen connector” does not exist. Pinning for various connectors, suitable in CANopen applications, are provided in CiA 106. For specific applications, CANopen profiles may provide a detailed connector specification. Cabling recommendations are provided in CiA 303-1. Environmental requirements to the intended application field may demand deviations from ISO 11898-2. Therefore, CANopen is open to other physical layer options. In case other physical layer options are used, the resulting CANopen device is not interoperable in most CANopen applications.