Library overview

Basic flow

Once initialized, the library handles all the low-level details:

• TX/RX tasks manage communication timing and framing

• Callbacks inform your application when data arrives

• No polling required - everything runs in background tasks

Features

• Dual-Mode Transport

  • Modbus RTU over RS-485 via UART, optional DE/RE control

  • Modbus TCP over WiFi/Ethernet/netif

• Flexible Application Layer

  • Client: synchronous/blocking or asynchronous reads/writes with result trackers or callbacks

  • Server: direct‐pointer or callback register access, automatic validation and exception handling

  • Bridge: link any two interfaces (RTU↔︎TCP, RTU↔︎RTU, TCP↔︎TCP) for transparent proxying

• Standards Compliance

  • 3.5-character silent intervals for RTU, broadcast rules, exception code semantics

  • Full coverage of all common Modbus Function Codes (0x01–0x10)

• Pragmatic Memory Approach

  • Zero dynamic allocation by default

  • Dynamic allocations optional: Server can use stack or controlled (no reallocations at runtime) heap storage for Modbus registers.

• Comprehensive Examples & Tests

  • Unity-based native tests for codec, hardware loopback tests for interface & application layers

Namespaces & components

• Modbus : general namespace for core & application components, compatible with all Modbus protocol fashions

  • Client : Client application class

  • Server : Server application class

  • Bridge : Bridge application class

  • Frame : abstraction for a Modbus frame (used in Client)

  • Word : abstraction for exposed Modbus registers (used in Server)

  • IWordStore, Static/DynamicWordStore: Word storage containers

• ModbusCodec : frame encoding/decoding & value conversion

• ModbusInterface : manages Modbus transport with a generic approach

  • IInterface : abstract class for all Transport layers

  • RTU : transport layer class for Modbus RTU

  • TCP : transport layer class for Modbus TCP

• ModbusHAL : HAL wrappers for physical input/output management in an event-driven fashion

  • UART : wrapper around ESP-IDF UART API to manage an RS485 link

  • TCP : wrapper around ESP-IDF Socket API to manage TCP transactions across any Network interface (Ethernet, WiFi, PPP...)