Question 1

How do I troubleshoot a Modbus TCP connection failure with node-red-contrib-modbus?

Accepted Answer

Start Node-RED with DEBUG=contribModbus* environment variable for detailed logs. The README recommends testing with modbus-serial directly if issues persist, as it's the underlying library.

Question 2

node-red-contrib-modbus vs writing custom Modbus code in Node.js?

Accepted Answer

This package saves time with pre-built Node-RED nodes and queue management, but for fine-grained control or non-Node-RED projects, a custom script using modbus-serial might be more flexible. It depends on your integration and performance requirements.

Question 3

How to install node-red-contrib-modbus on a Raspberry Pi running Node-RED?

Accepted Answer

Run npm install node-red-contrib-modbus in the Node-RED user directory (e.g., ~/.node-red). If you encounter build issues, try adding --unsafe-perm --build-from-source flags as suggested in the README.

Question 4

What Modbus function codes does node-red-contrib-modbus support?

Accepted Answer

It inherits support from modbus-serial, which includes common codes like read coils, read holding registers, and write operations. Check the modbus-serial documentation for a full list, as it's not detailed in the README.

Question 5

Can I use node-red-contrib-modbus for Modbus RTU over RS-485 serial?

Accepted Answer

Yes, it supports Serial and RTU buffered connections, making it suitable for RS-485 networks. Configure the serial port settings in the client node, and ensure proper hardware setup.

Question 6

How to handle errors in Modbus flows with this package?

Accepted Answer

Since v5.22+, nodes output error statuses that you can handle in your flow, such as using catch nodes or conditional logic. The package catches network errors to prevent crashes, but you must implement error handling in your Node-RED design.

modbus

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