Modbus RTU Tester is an Android RS485/Modbus RTU field tester for engineers and technicians. With a USB-RS485 converter, you can run read/write checks, scan Slave IDs, inspect TX/RX logs, and use AI diagnostics to turn timeouts, CRC mismatches, parameter errors, and register decoding issues into practical next-step checks without carrying a laptop.

When a device does not respond, values look wrong, or you are unsure whether the cause is wiring, baud/parity, Slave ID, function code, register map, or data format, the app helps narrow the problem from actual communication records and response patterns.

Key features

Modbus RTU read and write
Read coils, discrete inputs, holding registers, and input registers. Pro features also support write operations (0x05/0x06/0x0F/0x10) with read-back verification.

Single read and continuous polling
Send one request for a quick field check, or use controlled polling when repeated observation is needed.

Quick scan
Scan a Slave ID range to find responsive devices and preview the first returned value.

Bus monitor and history
Inspect TX/RX frames, recent communication history, errors, and response patterns. This helps trace timeouts, CRC mismatch, wrong Slave ID, noise, and unexpected frames.

Multi-format value view
When the data type is unclear, choose all to compare Hex, UInt16, Int16, Binary, plus adjacent-register 32-bit and Float32 interpretations.

Protocol templates
Use searchable protocol templates for common field devices. Favorites and custom test templates are stored locally. Free users can save up to 3 custom templates; Pro removes the app-side custom template count limit.

AI-assisted diagnosis
AI diagnostics are manually triggered and currently experimental. They use a compact diagnostic snapshot, TX/RX history, errors, and multi-format value interpretations to summarize likely causes and field checks, such as mismatched Slave ID/baud/parity, A/B wiring or GND reference issues, termination/noise, CRC mismatch, timeout, function code mismatch, register offset, or endian/data type interpretation. Results are for troubleshooting reference only and are not guaranteed to be complete or correct. Usage limits, trial access, and pricing may change later.

Free and Pro

Free: basic read testing, standard communication settings, local search/favorites, and limited custom templates.
Pro: advanced communication controls, continuous polling, quick scan, extended monitoring/history, protocol testing, and AI diagnosis access subject to server-side quota.

Typical use cases

Factory and on-site maintenance
Equipment commissioning and acceptance testing
RS485/Modbus troubleshooting
Register map verification
Solar inverter and industrial device communication checks

Privacy and data

Core connection settings, local templates, and history remain on the device. When you manually use cloud features such as AI diagnosis, protocol issue reports, notices, or roadmap feedback, only the necessary diagnostic snapshot or interaction metadata is sent to the backend. Full device documents and large raw logs are not uploaded by default. In-app purchases are handled through Google Play.

Hardware requirements

Android 7.0 (API 24) or newer.
Android phone or tablet with USB Host/OTG support.
USB-C to USB-A adapter when required by the phone.
USB-RS485 converter and correct RS485 A/B differential wiring.
Field device power, GND reference, and termination resistor should be checked when needed.

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Additional Information