What's the difference between Modbus protocol and CAN protocol?

The core difference between Modbus protocol and CAN protocol lies in their design positioning: Modbus is an application layer protocol for industrial equipment data exchange, relying on underlying buses such as RS485 and TCP; CAN is a bottom layer (physical+data link layer) protocol that balances data transmission and control, designed specifically for high reliability real-time control scenarios.

The key differences between the two can be compared from five core dimensions:

1. Protocol hierarchy:

-Modbus: Only defines application layer specifications and requires communication with underlying protocols such as RS485 (Modbus RTU) and Ethernet (Modbus TCP).

-CAN: Covering both the physical layer and the data link layer, it comes with a built-in lower-level communication mechanism and can directly implement data transmission based on CAN bus hardware.

2. Communication architecture:

-Modbus: It is mainly based on a "master-slave architecture", with only one master station initiating requests and the slave station passively responding, unable to actively report data.

-CAN: Adopting a "multi master architecture", all nodes have equal status and can actively send data, supporting priority transmission of emergency data (such as fault alarms).

3. Real time performance and reliability:

-Modbus: Medium real-time performance, relies on master station polling, has no priority mechanism, and is prone to data loss due to industrial interference (relying solely on CRC verification for recovery).

-CAN: Strong real-time performance, supports data priority arbitration (the smaller the ID, the higher the priority), comes with bit error detection, frame verification, and automatic retransmission mechanism, suitable for scenarios such as automotive and industrial control that require high reliability.

4. Transmission distance and number of nodes:

-Modbus (RTU): The maximum distance for a single RS485 bus is 1200 meters, and it can connect up to 32 slave stations (requiring repeater expansion).

-CAN: The maximum distance of a single segment bus is 1000 meters (at 5kbps baud rate), and it can connect up to 110 nodes. The hardware supports more flexible node expansion.

5. Application scenarios:

-Modbus is commonly used in industrial automation for "device monitoring" scenarios, such as data exchange between PLCs, sensors, and frequency converters, pursuing low cost and compatibility.

-CAN: commonly used in "real-time control" scenarios, such as automotive electronics (engine, chassis control), industrial machine tools (axis control), medical equipment, requiring fast response and high reliability.