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138 lines
7.7 KiB
138 lines
7.7 KiB
# Modbus Library for Arduino
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Allows your Arduino to communicate via Modbus protocol
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[](https://github.com/epsilonrt/modbus-arduino/releases)
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[](https://registry.platformio.org/libraries/epsilonrt/modbus-arduino)
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[](https://www.arduinolibraries.info/libraries/modbus-arduino)
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[](https://www.arduino.cc/)
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[](#)
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[](#)
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[](#)
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[](#)
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[](#)
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---
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<a href="https://modbus.org/">
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<img src="https://github.com/epsilonrt/modbus-arduino/raw/master/extras/modbus.png" alt="Modbus Logo" align="right" valign="top">
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</a>
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The Modbus is a master-slave protocol used in industrial automation and can be used in other areas, such as home automation.
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The Modbus generally uses serial RS-232 or RS-485 as physical layer (then called Modbus Serial) and
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TCP/IP via Ethernet or WiFi (Modbus TCP). But it is also possible to associate the Modbus application protocol on any other physical layer, such as the radio for example (with [MobdusRadio](https://github.com/epsilonrt/modbus-radio) for example).
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In the current version the library allows the Arduino operate **as a slave**, supporting Modbus Serial and
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Modbus over IP. For more information about Modbus see:
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* [Wikipedia article](https://en.wikipedia.org/wiki/Modbus)
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* [MODBUS Application Protocol Specification](http://www.modbus.org/docs/Modbus_Application_Protocol_V1_1b.pdf)
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* [MODBUS Messaging on TCP/IP Implementation Guide](http://www.modbus.org/docs/Modbus_Messaging_Implementation_Guide_V1_0b.pdf)
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* [MODBUS over serial line specification and implementation guide ](http://www.modbus.org/docs/Modbus_over_serial_line_V1_02.pdf)
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## Features
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* Operates as a slave (master mode in development)
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* Supports Modbus over Serial line (RS-232 or RS485) and Modbus TCP
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* Reply exception messages for all supported functions
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* Modbus functions supported:
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* 0x01 - Read Coils
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* 0x02 - Read Input Status (Read Discrete Inputs)
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* 0x03 - Read Holding Registers
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* 0x04 - Read Input Registers
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* 0x05 - Write Single Coil
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* 0x06 - Write Single Register
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* 0x0F - Write Multiple Coils
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* 0x10 - Write Multiple Registers
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* 0x11 - Report Server ID
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A set of examples is available for each of the Modbus-derived classes, for example:
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* [Lamp](https://github.com/epsilonrt/modbus-serial/blob/master/examples/Lamp/Lamp.ino): Use a coil to turn on and off a LED (0x05 and 0x01 functions)
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* [LampDimmer](https://github.com/epsilonrt/modbus-serial/blob/master/examples/LampDimmer/LampDimmer.ino): Use a holding register to control the brightness of a LED (0x06 and 0x03 functions)
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* [Switch](https://github.com/epsilonrt/modbus-serial/blob/master/examples/Switch/Switch.ino): Use a discrete input to read the state of a switch (0x02 function)
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* [TempSensor](https://github.com/epsilonrt/modbus-serial/blob/master/examples/TempSensor/TempSensor.ino): Use a input register to read the temperature from a sensor (0x04 function)
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* [Servo](https://github.com/epsilonrt/modbus-radio/blob/master/examples/Servo/Servo.ino): Use a holding register to control the position of a servo motor (0x06 an 0x03 function). Show how to define boundaries for the register.
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* [LampEncrypted](https://github.com/epsilonrt/modbus-radio/blob/master/examples/LampEncrypted/LampEncrypted.ino): Use a coil to turn on and off a LED (0x05 and 0x01 functions) with encrypted communication.
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All examples show the use of 0x11 function to report the slave ID.
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**Notes:**
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1. The offsets for registers are 0-based. So be careful when setting your supervisory system or your testing software. If offsets are 1-based, so a register configured as 100 in library should be 101 in this software.
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2. Early in the library Modbus.h file there is an option to limit the operation
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to the functions of Holding Registers, saving space in the program memory.
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Just comment out the following line:
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#define USE_HOLDING_REGISTERS_ONLY
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Thus, only the following functions are supported:
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* 0x03 - Read Holding Registers
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* 0x06 - Write Single Register
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* 0x10 - Write Multiple Registers
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You may test the library using the [MbPoll](https://github.com/epsilonrt/mbpoll) software. For example, to turn on the led in the Lamp example, just do:
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$ mbpoll -m rtu -b38400 -a10 -t0 /dev/tnt1 1
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mbpoll 1.5-2 - ModBus(R) Master Simulator
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Copyright (c) 2015-2023 Pascal JEAN, https://github.com/epsilonrt/mbpoll
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This program comes with ABSOLUTELY NO WARRANTY.
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This is free software, and you are welcome to redistribute it
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under certain conditions; type 'mbpoll -w' for details.
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Protocol configuration: ModBus RTU
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Slave configuration...: address = [10]
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start reference = 1, count = 1
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Communication.........: /dev/tnt1, 38400-8E1
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t/o 1.00 s, poll rate 1000 ms
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Data type.............: discrete output (coil)
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Written 1 references.
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## How to
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There are five classes corresponding to six headers that may be used:
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* Modbus-Arduino - Base Library (this repository)
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* [Modbus-Serial](https://github.com/epsilonrt/modbus-serial) - Modbus Serial RTU Library
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* [Modbus-Ethernet](https://github.com/epsilonrt/modbus-ethernet) - Modbus TCP Library (standard Ethernet Shield)
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* [Modbus-EtherCard](https://github.com/epsilonrt/modbus-ethercard) - Modbus TCP Library (for ENC28J60 chip)
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* [Modbus-Esp8266AT](https://github.com/epsilonrt/modbus-esp8266at) - Modbus IP Library (for ESP8266 chip with AT firmware)
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* [Modbus-Radio](https://github.com/epsilonrt/modbus-radio) - Modbus Radio Library (RadioHead compatible chips)
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By opting for Modbus Serial, TCP or Radio you must include in your sketch the corresponding header :
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#include <ModbusSerial.h>
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## Modbus Jargon
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In this library was decided to use the terms used in Modbus to the methods names, then is important clarify the names of
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register types:
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| Register type | Use as | Access | Library methods |
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| -------------------- | ------------------ | ----------------- | ----------------------------- |
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| Coil | Digital Output | Read/Write | addCoil(), coil(), setCoil() |
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| Holding Register | Analog Output | Read/Write | addHreg(), hreg(), setHreg() |
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| Input Status | Digital Input | Read Only | addIsts(), ists(), setIsts() |
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| Input Register | Analog Input | Read Only | addIreg(), ireg(), setIreg() |
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**Notes:**
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1. _Input Status_ is sometimes called _Discrete Input_.
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2. _Holding Register_ or just _Register_ is also used to store values in the slave.
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3. Examples of use: A _Coil_ can be used to drive a lamp or LED. A _Holding Register_ to
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store a counter or drive a Servo Motor. A _Input Status_ can be used with a reed switch
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in a door sensor and a _Input Register_ with a temperature sensor.
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License
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=======
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The code in this repo is licensed under the BSD New License. See LICENSE for more info.
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