mbus-core 0.2.0

Modbus client stack for embedded and std environments with TCP, RTU, and ASCII transport support
Documentation

mbus-core

mbus-core is a helper crate for modbus-rs.

It provides shared protocol types, transport abstractions, function-code definitions, and data models used by higher-level crates such as mbus-client, mbus-tcp, and mbus-serial.

What This Crate Provides

  • Core Modbus ADU/PDU data structures.
  • Function code enums and protocol constants.
  • Transport trait and transport configuration types.
  • Shared error model (MbusError) used across the workspace.
  • Feature-gated Modbus data models (coils, registers, etc.).
  • no_std-friendly implementation for embedded targets.

Helper Crate Role in the Workspace

mbus-core is intentionally low-level and reusable.

  • mbus-client builds request/response workflows on top of this crate.
  • mbus-tcp and mbus-serial implement concrete transport layers that satisfy interfaces defined here.
  • modbus-rs re-exports major crates for easier consumption.

This separation keeps protocol definitions centralized and avoids duplication across client and transport crates.

Module Overview

  • data_unit: ADU/PDU structures and framing helpers.
  • errors: Core error types used by all crates.
  • function_codes: Public and user-defined function code definitions.
  • models: Feature-gated Modbus data models.
  • transport: Transport traits, config types, and transport-related enums/errors.

Feature Flags

mbus-core supports selective compilation to reduce binary size.

Available feature flags:

  • serial-ascii
  • coils
  • registers
  • discrete-inputs
  • fifo
  • file-record
  • diagnostics

Default behavior:

  • default enables all features above.

serial-ascii affects ADU buffer sizing:

  • enabled: MAX_ADU_FRAME_LEN = 513 (ASCII upper bound)
  • disabled: MAX_ADU_FRAME_LEN = 260 (TCP/RTU upper bound)

This reduces stack usage in non-ASCII builds while preserving full ASCII compatibility when explicitly enabled.

Example with selective features:

[dependencies]
mbus-core = { version = "0.2.0", default-features = false, features = ["coils", "registers"] }

no_std

This crate is designed for embedded and constrained environments and is compatible with no_std usage patterns.

License

Copyright (C) 2025 Raghava Challari

This project is currently licensed under GNU GPL v3.0. See LICENSE for details.

Disclaimer

This is an independent Rust implementation of the Modbus specification and is not affiliated with the Modbus Organization.

Contact

For questions or support: