Based on the CAN bus standard, the maximum number of devices that can be connected to a CAN bus varies depending on the specific standard being used.
According to information found regarding the CAN bus standard, the limit on the number of devices is:
- 32
- 64
- 127
These numbers represent the maximum possible nodes (devices) that can be connected to a single CAN bus network segment, depending on the specific implementation or physical layer characteristics defined by the standard being followed.
Understanding the CAN Bus Device Limit
The primary factor limiting the number of devices on a CAN bus is the electrical load each device places on the network wiring. Each node connected to the bus adds capacitance and impedance, which can degrade the signal quality, especially at higher communication speeds and over longer distances.
Different standards or recommended practices related to the CAN physical layer (like ISO 11898-2) specify parameters that, when adhered to, ensure reliable communication. The typical driver/receiver circuits used in CAN transceivers are designed to handle a certain load, often corresponding to a maximum number of standard nodes.
Factors Influencing the Limit:
- Transceiver Capabilities: The specific CAN transceiver chip used in each device has driver strength and receiver sensitivity characteristics that affect how many other transceivers it can reliably communicate with.
- Network Topology and Length: While CAN is a bus topology, the physical length of the bus and the layout (stub lengths) impact signal integrity and the achievable node count.
- Data Rate: Higher data rates are more susceptible to signal reflections and attenuation, which can further reduce the practical limit on the number of nodes.
- Node Unit Load: Transceivers are often specified in terms of "unit loads." A standard transceiver might present 1 unit load, while some newer transceivers might present less (e.g., 1/2 or 1/4 unit load), allowing more nodes on the bus up to the maximum total unit loads supported by the network.
While the reference states 32, 64, or 127 devices depending on the standard, 32 is a commonly cited practical limit for standard CAN physical layers over typical lengths and speeds without special considerations. Achieving 64 or 127 nodes often requires using specific transceivers with lower unit loads or potentially segmenting the network with repeaters (though repeaters have their own implications).
Summary of Maximum Devices:
| Standard/Condition | Maximum Devices |
|---|---|
| Depending on standard | 32 |
| Depending on standard | 64 |
| Depending on standard | 127 |
It's crucial to consult the documentation for the specific CAN transceivers and standards being implemented in a system to determine the exact maximum number of nodes supported while maintaining reliable communication.
