Modbus RTU & ASCII is a Windows client and server tool designed to help you develop, configure, and troubleshoot serial Modbus devices. Connect to Modbus RTU or ASCII devices through a COM port, then read or write Coils, Discrete Inputs, Input Registers, and Holding Registers. Configure up to five client sessions to work with multiple devices in one workspace, and monitor changing values with manual reads or scheduled polling. The built-in server mode lets you configure multiple Unit IDs on a single COM port and edit their data maps. Fixed, increasing, decreasing, and random value generators make it easy to simulate responses and changing data without physical equipment, providing a practical environment for development and testing. Inspect transmitted and received frames together with decoded requests and responses in the log viewer. Export logs to CSV, save diagnostic information, and import or export client sessions and server settings as reusable profiles. Supported display formats include Boolean, UInt16, Int16, UInt32, Int32, Float32, Float64, Hex, Binary, and ASCII, with configurable byte and word order. App settings, profiles, and logs are stored locally on your device. No account or cloud synchronization is required. Common use cases: - Check connections to PLCs, sensors, instruments, and serial Modbus devices - Inspect Modbus RTU/ASCII requests and responses - Read, write, and monitor registers and Coils - Simulate a server with multiple Unit IDs - Analyze communication logs and export test results Important: Always verify the target address, data format, and value before writing to real equipment. Key features - Modbus RTU and Modbus ASCII support - Client mode and multi-Unit ID server mode - Up to five client sessions - FC01, FC02, FC03, and FC04 read operations - FC05, FC06, FC15, and FC16 write operations - Manual reads and scheduled polling - Coil, Discrete Input, Input Register, and Holding Register data maps - Multiple numeric and text formats with byte and word order controls - Fixed, increasing, decreasing, and random value generators - Decoded request/response and raw serial frame logs - CSV log and diagnostic data export - Client and server profile import/export - Korean and English UI with light and dark themes - Local-first operation with no account or cloud connection required