Modbus Library for Arduino

ModbusRTU, ModbusTCP and ModbusTCP Security

If the library is helpful for your projects you can support it by a glass of beer

The library is under active development. Visit Releases page for stable one.

This library allows your Arduino board to communicate via Modbus protocol. The Modbus is a protocol used in industrial automation and also can be used in other areas, such as home automation.

The Modbus generally uses serial RS-485 as physical layer (then called Modbus Serial) and TCP/IP via Ethernet or WiFi (Modbus TCP).

Features

Supports all Arduino platforms
Operates in any combination of multiple instances of
- Modbus RTU slave
- Modbus RTU master
- Modbus TCP server for ESP8266/ESP32 and Ethernet library
- Modbus TCP client for ESP8266/ESP32 and Ethernet library
- MODBUS/TCP Security server (ESP8266)
- MODBUS/TCP Security client (ESP8266/ESP32)
Reply exception messages for all supported functions
Modbus functions supported:
- 0x01 - Read Coils
- 0x02 - Read Input Status (Read Discrete Inputs)
- 0x03 - Read Holding Registers
- 0x04 - Read Input Registers
- 0x05 - Write Single Coil
- 0x06 - Write Single Register
- 0x0F - Write Multiple Coils
- 0x10 - Write Multiple Registers
- 0x14 - Read File Record
- 0x15 - Write File Record
- 0x16 - Mask Write Register
Callbacks for
- Client connect (Modbus TCP)
- Server/Client disconnect (Modbus TCP)
- Read specific Register
- Write specific Register
- Slave transaction finish

Notes

The offsets for registers are 0-based. So be careful when setting your supervisory system or your testing software. For example, in ScadaBR offsets are 0-based, then, a register configured as 100 in the library is set to 100 in ScadaBR. On the other hand, in the CAS Modbus Scanner offsets are 1-based, so a register configured as 100 in library should be 101 in this software.
For API refer API.md
RS-485 transivers based on MAX-485 is working on at least up to 115200. XY-017/XY-485 working only up to 9600 for some reason.

For more information about Modbus see:

Last Changes

// 4.0.0-DEV
+ ModbusTLS: Modbus TCP Security Client/Server
+ ModbusTLS: ESP8266 Client/Server
+ Test: TLS ESP8266 Client/Server
+ Examples: TLS added
- Examples: TLS Certificate test Role extension and Alt-Name
- Examples: TLS Add example explanation
+ ModbusTLS: ESP32 Client
- Test: TLS ESP32 Client
+ Build with no STL dependency
- Test: No-STL mode
+ ModbusTCP: ModbusEthernet - W5x00 Ethernet library support
+ Test: W5x00 support
- Test: W5x00 with Ethernet library v1
+ API: Implementation code merge
+ API: Access ModbusTCP server by name
+ API: Set local multiple registers from an array
+ ModbusIP => ModbusTCP
+ 0x14 - Read File Records function
+ Test: 0x14
+ 0x15 - Write File Records function
+ Test: 0x15
- Examples: Basic file operations
- Examples: FW update
+ 0x16 - Write Mask Register function
- Test: 0x16
- 0x17 - Read/Write Registers function
- Test: 0x17
+ API: Access control callback for individual Modbus function
- Slave/Server: slavePDU use early exit by return where possible
- Master/Client: Check frame size against header data where possible
- Master/Client: Additional responce data validation
- Test: push/pull functions
- Test: Frame accuracy to specefication
- Documentation: Update
- Examples: Revising
+ ModbusRTU: ESP32 SoftwareSerial support
+ ModbusRTU: Fix transaction callback remains assigned after request end
+ ModbusTCP: Free server connection in destructor
+ Declare global registers and callbacks as static members
- Free global registers and callbacks on remove last Modbus instance
+ ModbusRTU: Refactor .task() for more relaibe processing of incoming data
+ API: Declare all callbacks as std::function (for STL)
- API: Msater/Slave => Client/Server according to [PRESS RELEASE](https://modbus.org/docs/Client-ServerPR-07-2020-final.docx.pdf)
// 4.1.0
- ModbusTLS: ESP32 Server
- Test: TLS ESP32 Server