emModbus

SEGGER emModbus is a compact, production-grade Modbus protocol stack designed for resource-constrained embedded systems in industrial automation, building management, and process control applications. It implements the full Modbus specification across all transport variants, RTU and ASCII framing over UART, plus Modbus/TCP and Modbus/UDP over Ethernet, giving developers a single library that covers both serial and networked Modbus communication. With a master footprint of approximately 2.5 KB ROM and a slave footprint of around 3 KB ROM, emModbus fits comfortably on the smallest microcontrollers while maintaining full protocol compliance.

Master and Slave Editions

emModbus is available in separate Master and Slave configurations, each with a complete API and ready-to-run sample applications for all supported protocols. Both editions include companion Windows applications (provided as binary and source) for testing and development without dedicated hardware. The stack uses no dynamic memory allocation, ensuring deterministic behaviour and eliminating heap fragmentation concerns that are critical in long-running industrial systems.

Feature	Master	Slave
ROM	~2.5 KB	~3 KB
RAM	~30 bytes + 300 bytes/channel	~30 bytes + 300 bytes/channel
UART protocols	RTU, ASCII	RTU, ASCII
Ethernet protocols	TCP, UDP	TCP, UDP
Windows test tools	Included (binary + source)	Included (binary + source)

Integration and Portability

Written in ANSI C with a clean hardware abstraction layer, emModbus is fully portable across compilers and target platforms. For Ethernet operation it works with any TCP/IP stack that provides a BSD socket interface, and it is optimised for use with SEGGER emNet. A kernel abstraction layer provides native integration with embOS on embedded targets and Windows for desktop development. The royalty-free licensing model, one-time payment with no per-unit fees, keeps production costs predictable across volume ramps in industrial deployments.