Modbus Field Tester

Modbus Field Tester is an Android Modbus RTU and Modbus TCP field tester for engineers and technicians. Connect a USB-RS485 converter for serial equipment, or enter a private-network host and port for Modbus TCP. You can run read/write checks, inspect communication records, and use AI-assisted diagnosis without carrying a laptop. When a device does not respond or values look wrong, the app helps separate RTU wiring and serial-setting issues from TCP address, port, Unit ID, socket, MBAP, and response-time issues. Key features Manual RTU and TCP tests Enter RTU serial settings or a TCP host and port, then choose the request Unit ID, function code, address, and quantity. Read coils, discrete inputs, holding registers, and input registers. Write functions 0x05, 0x06, 0x0F, and 0x10 use a confirmation preview before the request is sent. Single request and Pro continuous polling Send one request for a quick field check. Pro adds controlled continuous polling when repeated observation is needed. RTU Quick Scan and private-network TCP discovery Pro can scan RTU Slave IDs or look for Modbus TCP endpoints on the current private Wi-Fi/Ethernet subnet. Automatic discovery does not scan public IP, cellular, VPN, or background networks. Timing, values, and communication history Review round-trip time, TX/RX frames, recent history, errors, and response patterns. Compare Hex, UInt16, Int16, Binary, UInt32, and Float32 interpretations. RTU diagnosis covers CRC and serial settings; TCP diagnosis covers refused/timeout/reset errors, MBAP validation, and transaction or Unit ID mismatch. Protocol templates Search common field-device templates, keep favorites, and save local custom tests. Free users can save up to 3 custom templates; Pro removes the app-side custom-template count limit. AI-assisted diagnosis AI diagnosis is manually triggered and uses a compact snapshot that you can review before upload. It classifies RTU and TCP evidence separately and returns safe troubleshooting suggestions; it does not automatically send Modbus write requests. Free includes 3 manual diagnoses per day and 10 per month. Pro provides a higher quota. Free and Pro Free: manual RTU/TCP connection, single read/write requests, standard settings, local templates/history, and the manual AI quota. Pro: automatic TCP discovery, RTU Quick Scan, continuous polling, advanced communication settings, all TX/RX raw logs in the retained buffer (up to 60 entries), a higher AI quota, and no ads. Typical use cases Factory and on-site maintenance Equipment commissioning and acceptance testing RS485/Modbus RTU troubleshooting Modbus TCP endpoint and register-map verification Solar inverter and industrial-device communication checks Privacy and data Connection profiles, local templates, and history remain on the device. Private-network discovery stays on the current local network. Cloud features such as AI diagnosis, protocol issue reports, notices, or roadmap feedback send only the required snapshot or interaction metadata after user action. Full device documents and large raw logs are not uploaded by default. In-app purchases are handled through Google Play. Requirements Android 7.0 (API 24) or newer. For RTU: Android USB Host/OTG support, a USB-RS485 converter, and correct RS485 A/B wiring. For TCP: access to the target device on a private Wi-Fi or Ethernet network.