Why do a simple industrial control project require three communication protocols, namely Modbus, CAN and EtherCAT? The following illustrates the architecture of a typical small-scale industrial control system. Why do the three industrial buses perform their respective functions instead of adopting a single bus for all tasks?
In fact, almost all PLCs, motion controllers and robots follow this design principle:
- EtherCAT → Real-time motion control and I/O communication
- CANopen → Drivers, servo drives and stepper motors
- Modbus RTU → Meters and sensors
The three protocols run on the same CPU (Raspberry Pi) and are scheduled simultaneously by different Linux threads.
Essentially, they are three completely independent software protocol stacks:
- EtherCAT Master
- CANopen Master
- Modbus Master
with no mutual interference between each other.
Why use EtherCAT for stepper motor limit control?
Limit signals belong to high-speed safety digital I/O, which requires ultra-low latency, hard real-time performance and precise synchronization. Among the three buses, EtherCAT is the only one that meets the above requirements, unlike CANopen and Modbus.
Why is this functional division the industry best practice?
| Function | Bus Protocol | Reason |
|---|---|---|
| Stepper motor control | CANopen | Standardized driver design, real-time control via PDO, and simple wiring |
| Left and right limit detection | EtherCAT | Short cycle time and high determinism, suitable for high-speed digital I/O scenarios |
| Temperature and humidity monitoring | Modbus RTU | Wide compatibility with mainstream meters, simple implementation and low cost |
| Upper computer/HMI communication | Ethernet (TCP/IP) | Convenient for data upload, real-time monitoring and parameter configuration |
This architecture is consistent with the typical communication layering of industrial equipment such as PLCs, motion controllers, robots and AGVs. Specifically, EtherCAT is responsible for high-speed real-time control, CANopen for intelligent drive equipment, and Modbus RTU for low-speed on-site instruments.
Extended Technical Topics
- Why does a simple industrial control project require Modbus, CAN, and EtherCAT?
- Why CAN alone is insufficient, and a complete CANopen architecture is mandatory for motion control?
- Fundamentals of CANopen Motion Control Safety Procedures
- How Does EtherCAT Achieve Low Latency?
- EtherCAT Low-Latency Communication: Physical Layer Reference Circuit
- Modbus RTU Working Principle: Master-Slave Architecture and Polling Mechanism
- Modbus RTU Communication Process