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Most complete Modbus library for Arduino. A library that allows your Arduino board to communicate via Modbus protocol, acting as a master, slave or both. Supports network transport (Modbus TCP) and Serial line/RS-485 (Modbus RTU). Supports Modbus TCP Security for ESP8266/ESP32.

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Modbus Library for Arduino

ModbusRTU, ModbusTCP and ModbusTCP Security

For detailes on the library usage visitdocumentation section.

Features

Supports all Arduino platforms
Operates in any combination of multiple instances of
- Modbus RTU server
- Modbus RTU client
- Modbus TCP server forESP8266/ESP32 andEthernet library
- Modbus TCP client forESP8266/ESP32 andEthernet 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, inScadaBR offsets are 0-based, then, a register configured as 100 in the library is set to 100 in ScadaBR. On the other hand, in theCAS 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

// 4.1.1+ Protocol: Fix wrong error code responce on non-existent register+ ModbusTCP: Fix potential memory leak+ API: cbEnable/cbDisable functionality extended+ ESP-IDF: CMakeList.txt added+ Examples: TCP-to-RTU fixed// 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- 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- 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