Building a Custom Modbus TCP Client in .NET: What a Production-Grade Poller Actually Needs

Short summary

A practical guide to building the application layer around Modbus TCP libraries in .NET — the part tutorials skip. Covers connection lifecycle for devices that disappear and return, per-device polling schedules that tolerate slow peers, decoding raw 16-bit registers into typed values (including big-endian float reconstruction), and data routing decoupled from acquisition. Includes runnable code against a simulated device with zero external dependencies.

• •Modbus libraries give you a read call, not a deployable client — connection lifecycle, polling, decoding, and observability are custom work
• •32-bit floats span two registers in big-endian order; wrong byte order produces plausible-looking wrong numbers, not errors
• •Register definitions as data (not scattered logic) keep decoding maintainable across device types

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