Issue
Can two IC3-Modbus controllers be configured to interrogate a single Modbus TCP slave device?
Product Line
Satchwell BAS & Sigma
Environment
Satchwell Sigma IC3-Modbus
Cause
A backup or redundant configuration may be required for reliability or failover purposes, prompting the need to connect multiple IC3-Modbus controllers to a single Modbus slave.
Resolution
Yes, this configuration is acceptable when using Modbus TCP protocol. However, it is not supported in RS485 RTU environments.
-
Modbus TCP Configuration:
- Each Modbus device on a TCP network must have a unique ID.
- Other parameters such as register address, data type, and Gateway IP address can be identical across controllers.
- This allows multiple IC3-Modbus controllers to query the same slave device without conflict.
-
RS485 RTU Configuration:
- Only one master device is allowed per RS485 RTU network.
- Attempting to use multiple masters will result in communication conflicts and is not supported.
Best Practices
- Ensure each controller has a distinct Modbus ID when configuring TCP.
- Avoid simultaneous polling from both controllers unless the slave device supports concurrent connections.
- Monitor network traffic to prevent overload or latency issues.
