A free, open-source Qt-based implementation of a Modbus master application. It includes a bus monitor for examining traffic.
For a tool that is vital to your career, the one-time license fee is a small investment compared to the time saved during troubleshooting. Free Alternatives to Modbus Poll modbus poll registration key generator
If you encounter a bug or need help configuring a complex Modbus RTU network, the developers (Witte Software) will not provide support for unlicensed copies. A free, open-source Qt-based implementation of a Modbus