Modbus Library for Arduino

ModbusRTU, ModbusTCP and ModbusTCP Security

For detailes on the library usage visit documentation section.

Features

Supports all Arduino platforms
Operates in any combination of multiple instances of
- Modbus RTU server
- Modbus RTU client
- 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)
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
- 0x17 - Read/Write multiple registers
Callbacks driven design
Real life complex examples:
- ESP8266/ESP32 firmware update over Modbus
- ModbusRTU to ModbusTCP bridge

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.
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

// 4.1.0
+ API: Raw Modbus frame processing functionality
+ ModbusRTU: Precise inter-frame interval control
+ Examples: True ModbusRTU to ModbusTCP Server bridge
+ Examples: ModbusRTU respond to multiple ID from single device
+ ModbusRTU: Add direction control pin for Stream
+ STL: Add Reg count limitation to vector limit of 4000 (for ESP8266 and ESP32)
+ Settings: Added MODBUSIP_CONNECTION_TIMEOUT (ESP32 only)
+ Settings: Set MODBUSIP_MAX_CLIENTS = 8 for ESP32
+ ModbusTCP: Make using DNS names optional feature
+ ModbusRTU: Add separate RE/DE pins control optional feature
+ API: Drop support of Ethernet library v1
+ Examples: Teknic ClearCore ArduinoWrapper examples added
+ Examples: ModbusTCP to ModbusRTU example added
+ ModbusRTU: Flush extra delay optional feature
// 4.0.0
+ Support of all Arduino boards
+ ModbusTLS: ESP8266 Client/Server and ESP32 Client
+ ModbusTCP: ModbusEthernet - WizNet W5x00, ENC28J60 Ethernet library support
+ 0x14 - Read File Records function
+ 0x15 - Write File Records function
+ Examples: FW update over Modbus fullfunctional example
+ 0x16 - Write Mask Register function+ Test: 0x16
+ 0x17 - Read/Write Registers function
+ ModbusRTU: ESP32 SoftwareSerial support
+ Build with no STL dependency (switchable)
+ API: ModbusIP => ModbusTCP
+ API: Access control callback for individual Modbus function
+ API: Master/Slave => Client/Server according to [PRESS RELEASE](https://modbus.org/docs/Client-ServerPR-07-2020-final.docx.pdf)
+ Lot of code refacting and small fixes

Roadmap

// 4.2.0-DEV
- API: Alternative CRC calulation (reduced memory footprint)
- ModbusRTU: Static buffer allocation
- Test: Frame accuracy to specefication
- Buffer/packet size limitation support
- 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
- Free global registers and callbacks on remove last Modbus instance
- Test: push/pull functions
- ModbusTCP: Refactor connect by dns name (using native implementation for ESP32 etc)
// 4.3.0-DEV
- ModbusTLS: ESP32 Server
- Test: TLS ESP32 Server
- Test: TLS ESP32 Client
- Examples: TLS Certificate test Role extension and Alt-Name
- Examples: TLS Add example explanation
- ModbusTCP: ModbusAsyncTCP
- API: Extend API to allow custom Modbus commands
- Examples: Basic file operations
- Examples: Revising