modbus-serial

A pure JavaScript implementation of MODBUS-RTU (Serial and TCP) for NodeJS.

Modbus is a serial communications protocol, first used in 1979. Modbus is simple and robust, openly published, royalty-free and easy to deploy and maintain.

This package makes Modbus calls and serve fun and easy.

---

• What can I do with this module ?
• Compatibility
• Examples
• Methods

---

Install

npm install modbus-serial

try these options on npm install to build, if you have problems to install

--unsafe-perm --build-from-source

What can I do with this module ?

This class makes it fun and easy to communicate with electronic devices such as irrigation controllers, protocol droids and robots. It talks with devices that use a serial line (e.g. RS485, RS232). Many industrial electronic devices implement modbus. Arduino can also talk modbus and you can control your projects and robots using modbus.

Arduino libraries for modbus slave:

• https://github.com/yaacov/arduino-modbus-slave
• https://github.com/smarmengol/Modbus-Master-Slave-for-Arduino

Arduino sketch for irrigation timer with modbus support:

• https://github.com/yaacov/arduino-irrigation-timer

Node Modbus-WebSocket bridge:

• https://github.com/yaacov/node-modbus-ws

Compatibility

Version of NodeJS:

This module has not been tested on every single version of NodeJS. For best results you should stick to LTS versions, which are denoted by even major version numbers e.g. 4.x, 6.x, 8.x.

These classes are implemented:

Class	Function
FC1 "Read Coil Status"	readCoils(coil, len)
FC2 "Read Input Status"	readDiscreteInputs(addr, arg)
FC3 "Read Holding Registers"	readHoldingRegisters(addr, len)
FC4 "Read Input Registers"	readInputRegisters(addr, len)
FC5 "Force Single Coil"	writeCoil(coil, binary) //NOT setCoil
FC6 "Preset Single Register"	writeRegister(addr, value)
FC15 "Force Multiple Coil"	writeCoils(addr, valueAry)
FC16 "Preset Multiple Registers"	writeRegisters(addr, valueAry)
FC43/14 "Read Device Identification" (supported ports: TCP, RTU)	readDeviceIdentification(id, obj)

Client Serial:

• modbus-RTU (SerialPort): Over serial line [require node serialport].
• modbus-RTU (RTUBufferedPort): Over buffered serial line [require node serialport].
• modbus-ASCII (AsciiPort): Over serial line [require node serialport].

Client TCP:

• modbus-TCP (TcpPort): Over TCP/IP line.
• modbus-RTU (UdpPort): Over C701 server, commercial UDP to serial bridge.
• modbus-RTU (TcpRTUBufferedPort): Over TCP/IP line, TCP/IP serial RTU buffered device.
• modbus-RTU (TelnetPort): Over Telnet server, TCP/IP serial bridge.

Server

• modbus-TCP (ServerTCP): Over TCP/IP line.

Examples

Read and Write

// create an empty modbus client
const ModbusRTU = require("modbus-serial");
const client = new ModbusRTU();

// open connection to a serial port
client.connectRTUBuffered("/dev/ttyUSB0", { baudRate: 9600 }, write);

function write() {
    client.setID(1);

    // write the values 0, 0xffff to registers starting at address 5
    // on device number 1.
    client.writeRegisters(5, [0 , 0xffff])
        .then(read);
}

function read() {
    // read the 2 registers starting at address 5
    // on device number 1.
    client.readHoldingRegisters(5, 2)
        .then(console.log);
}

---

Read on multiple slaves

const ModbusRTU = require("modbus-serial");
// create an empty modbus client
const client = new ModbusRTU();
// open connection to a serial port
client.connectRTUBuffered("/dev/ttyS0", { baudRate: 9600 });
// set timeout, if slave did not reply back
client.setTimeout(500);

// list of meter's id
const metersIdList = [10, 11, 12, 13, 14];

const getMetersValue = async (meters) => {
    try{
        // get value of all meters
        for(let meter of meters) {
            // output value to console
            console.log(await getMeterValue(meter));
            // wait 100ms before get another device
            await sleep(100);
	}
    } catch(e){
        // if error, handle them here (it should not)
        console.log(e)
    } finally {
        // after get all data from slave, repeat it again
        setImmediate(() => {
            getMetersValue(metersIdList);
        })
    }
}

const getMeterValue = async (id) => {
    try {
        // set ID of slave
        await client.setID(id);
        // read the 1 registers starting at address 0 (first register)
        let val =  await client.readInputRegisters(0, 1);
        // return the value
        return val.data[0];
    } catch(e){
        // if error return -1
        return -1
    }
}

const sleep = (ms) => new Promise(resolve => setTimeout(resolve, ms));


// start get value
getMetersValue(metersIdList);

---

Logger Serial

// create an empty modbus client
const ModbusRTU = require("modbus-serial");
const client = new ModbusRTU();

// open connection to a serial port
client.connectRTUBuffered("/dev/ttyUSB0", { baudRate: 9600 });
client.setID(1);

// read the values of 10 registers starting at address 0
// on device number 1. and log the values to the console.
setInterval(function() {
    client.readHoldingRegisters(0, 10, function(err, data) {
        console.log(data.data);
    });
}, 1000);

---

Logger TCP

// create an empty modbus client
const ModbusRTU = require("modbus-serial");
const client = new ModbusRTU();

// open connection to a tcp line
client.connectTCP("127.0.0.1", { port: 8502 });
client.setID(1);

// read the values of 10 registers starting at address 0
// on device number 1. and log the values to the console.
setInterval(function() {
    client.readHoldingRegisters(0, 10, function(err, data) {
        console.log(data.data);
    });
}, 1000);

---

Logger UDP

// create an empty modbus client
const ModbusRTU = require("modbus-serial");
const client = new ModbusRTU();

// open connection to a udp line
client.connectUDP("127.0.0.1", { port: 8502 });
client.setID(1);

// read the values of 10 registers starting at address 0
// on device number 1. and log the values to the console.
setInterval(function() {
    client.readHoldingRegisters(0, 10, function(err, data) {
        console.log(data.data);
    });
}, 1000);

---

ModbusTCP Server

// create an empty modbus client
const ModbusRTU = require("modbus-serial");
const vector = {
    getInputRegister: function(addr, unitID) {
        // Synchronous handling
        return addr;
    },
    getHoldingRegister: function(addr, unitID, callback) {
        // Asynchronous handling (with callback)
        setTimeout(function() {
            // callback = function(err, value)
            callback(null, addr + 8000);
        }, 10);
    },
    getCoil: function(addr, unitID) {
        // Asynchronous handling (with Promises, async/await supported)
        return new Promise(function(resolve) {
            setTimeout(function() {
                resolve((addr % 2) === 0);
            }, 10);
        });
    },
    setRegister: function(addr, value, unitID) {
        // Asynchronous handling supported also here
        console.log("set register", addr, value, unitID);
        return;
    },
    setCoil: function(addr, value, unitID) {
        // Asynchronous handling supported also here
        console.log("set coil", addr, value, unitID);
        return;
    },
    readDeviceIdentification: function(addr) {
        return {
            0x00: "MyVendorName",
            0x01: "MyProductCode",
            0x02: "MyMajorMinorRevision",
            0x05: "MyModelName",
            0x97: "MyExtendedObject1",
            0xAB: "MyExtendedObject2"
        };
    }
};

// set the server to answer for modbus requests
console.log("ModbusTCP listening on modbus://0.0.0.0:8502");
const serverTCP = new ModbusRTU.ServerTCP(vector, { host: "0.0.0.0", port: 8502, debug: true, unitID: 1 });

serverTCP.on("socketError", function(err){
    // Handle socket error if needed, can be ignored
    console.error(err);
});

---

Read and Write Modbus ASCII

// create an empty modbus client
const Modbus = require("modbus-serial");
const client = new Modbus();

// open connection to a serial port
client.connectAsciiSerial(
    "/dev/ttyUSB0", 
    {
        baudRate: 9600,
        startOfSlaveFrameChar: 0x3A  // optional: slave frame delimiter
    }, 
    write);

function write() {
    client.setID(1);

    // write the values 0, 0xffff to registers starting at address 5
    // on device number 1.
    client.writeRegisters(5, [0 , 0xffff])
        .then(read);
}

function read() {
    // read the 2 registers starting at address 5
    // on device number 1.
    client.readHoldingRegisters(5, 2)
        .then(console.log);
}

---

"modbusdb" is an elegant wrapper over the Modbus protocol

Check modbusdb github repo at https://github.com/yarosdev/modbusdb for more information, feedback is welcome!

Here is an example of using modbusdb wrapper over modbus-serial:

import Modbus from 'modbus-serial';
import { Modbusdb, ModbusSerialDriver, Datamap, createRegisterKey, TypeEnum, ScopeEnum } from "modbusdb";

// create an empty modbus client
const client = new Modbus();

client.connectTcpRTUBuffered("127.0.0.1", { port: 8502 }, app) // or use any other available connection methods

function app() {

  // First you need to define a schema for a database:
  // createRegisterKey(UNIT_ADDRESS, MODBUS_TABLE, REGISTER_ADDRESS, BIT_INDEX)
  const schema = [
    { key: createRegisterKey(1, ScopeEnum.InternalRegister, 10),    type: TypeEnum.Int16 },
    { key: createRegisterKey(1, ScopeEnum.InternalRegister, 11),    type: TypeEnum.Int32 },
    { key: createRegisterKey(1, ScopeEnum.PhysicalRegister, 99),    type: TypeEnum.UInt16 },
    { key: createRegisterKey(1, ScopeEnum.InternalRegister, 15, 2), type: TypeEnum.Bit },
  ];
  
  // Define unit-scoped config if needed:
  const units = [
    {
      address: 1, // This is unit address
      forceWriteMany: true, // Use 15(0x0f) and 16(0x10) functions for single register, default: false
      bigEndian: true, // You can use BigEndian for byte order, default: false
      swapWords: false, // This is applicable only for multi-registers types such as int32, float etc, default: false
      requestWithGaps: true, // If you are requesting addresses 10 and 13, allow to send one request to the device, default: true
      maxRequestSize: 32, // How many registers to be requested in one round-trip with device, default: 1
    }
  ];
  
  // Let`s create an instance of a database:
  const db = new Modbusdb({
    driver: new ModbusSerialDriver(client),
    datamap: new Datamap(schema, units)
  });

  // Now we can request three registers:
  // NOTICE: Modbusdb under the hood will make all needed requests for you in using an optimal plan
  //         If registers can be requested using a single request, be sure it will
  db.mget([
    createRegisterKey(1, ScopeEnum.InternalRegister, 10),
    createRegisterKey(1, ScopeEnum.InternalRegister, 11),
    createRegisterKey(1, ScopeEnum.PhysicalRegister, 99)
  ]).then(result => {
    console.log('mget', result)
  })

  // You can store register`s key to be used later:
  const speedSetPoint = createRegisterKey(1, ScopeEnum.InternalRegister, 10);
  const workingMode = createRegisterKey(1, ScopeEnum.InternalRegister, 11);
  
  // Write values directly into modbus device as easy as possible:
  // NOTICE: Modbusdb under the hood will make all needed requests for you
  //         Write operations have higher priority over the read operations
  db.mset([
    [speedSetPoint, 60],
    [workingMode, 10],
  ]).then(result => {
    console.log('mset', result)
  })
}

Enums:

ScopeEnum: (Modbus Table)
  1 = PhysicalState = Discrete Input
  2 = InternalState = Coil Status
  3 = PhysicalRegister = Input Register
  4 = InternalRegister = Holding Register
  
TypeEnum: (Available Data Types)
  1 = Bit,
  4 = Int16,
  5 = UInt16,
  6 = Int32,
  7 = UInt32,
  8 = Float

---

to get more see Examples

Serial connection

node-modbus-serial use node-serialport for serial communication, for serial port options settings it passes to serial port the openOptions object, default serial port settings are 9600,8,n,1.

client.connectRTUBuffered("/dev/ttyUSB0", { baudRate: 9600, parity: 'even' });