modbus-serial

A pure JavaScript implemetation of MODBUS-RTU (and TCP) for NodeJS

This class makes ModbusRTU (and TCP) calls fun and easy.

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.

---

• Install
• What can I do with this module ?
• Compatibility
• Examples
• Methods - API Promises - API Callbacks - API connection shorthand

---

Install

npm install modbus-serial

For use over serial port (ModbusRTU), also install node-serialport:

npm install serialport

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

This class implements:

• FC1 "Read Coil Status"
• FC2 "Read Input Status"
• FC3 "Read Holding Registers"
• FC4 "Read Input Registers"
• FC5 "Force Single Coil"
• FC6 "Preset Single Register"
• FC15 "Force Multiple Coil"
• FC16 "Preset Multiple Registers"

Connects types:

• modbus-RTU (modbus-rtu): Over serial line [require node serialport].
• modbus-ASCII (modbus-ascii): Over serial line [require node serialport].
• modbus-TCP (modbus-tcp): Over TCP/IP line.
• modbus-RTU (telnet): Over Telnet server, TCP/IP serial bridge.
• modbus-RTU (buffered): Over buffered serial line [require node serialport].
• modbus-RTU (C701): Over C701 server, commercial UDP to serial bridge.

Examples

---

Logger

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

// open connection to a tcp line
client.connectTCP("192.168.1.42", run);

// read the values of 10 registers starting at address 0
// on device number 1. and log the values to the console.
function run() {
    client.setID(1);

    client.readInputRegisters(0, 10)
        .then(console.log)
        .then(run);
}

---

Read and Write

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

// open connection to a serial port
client.connectRTU("/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);
}

---

Logger

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

// open connection to a serial port
client.connectRTU("/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
var ModbusRTU = require("modbus-serial");
var client = new ModbusRTU();

// open connection to a tcp line
client.connectTCP("192.168.1.42");
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);

---

Read raw buffer

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

// open connection to a serial port
client.connectRTU("/dev/ttyUSB0", {baudrate: 9600}, run);

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

    // read 2 16bit-registers to get one 32bit number
    client.readInputRegisters(5, 2, function(err, data) {
        var int32 = data.buffer.readUInt32BE();
        console.log(int32);
    });
}

Methods

---

API promises

---

This communication functions use a pre-set unit-id and can return a promise, Using callbacks is optional.

// set the client's unit id
client.setID(1);

// read 8 discrete inputs starting at input 10
// (function use the unit id 1, we set earlier)
client.readDiscreteInputs(10, 8)
    .then(function(data) {
        console.log(data);
    });

---

.setID(id)

  Sets the unit id

id {number}: The new client id

---

.readCoils (address, length)

  Writes "Read Coils" (FC=1) request to serial port.

address {number}: The Data Address of the first register.

length {number}: The total number of registers requested.

---

.readDiscreteInputs (address, length)

  Writes "Read Discrete Inputs" (FC=2) request to serial port.

address {number}: The Data Address of the first register.

length {number}: The total number of registers requested.

---

.readHoldingRegisters (address, length)

  Writes "Read Holding Registers" (FC=3) request to serial port.

address {number}: The Data Address of the first register.

length {number}: The total number of registers requested.

---

.readInputRegisters (address, length)

  Writes "Read Input Registers" (FC=4) request to serial port.

address {number}: The Data Address of the first register.

length {number}: The total number of registers requested.

---

.writeCoil(address, state)

  Writes "Force Coil Status" (FC=5) request to serial port.

address {number}: The Data Address of the first register.

state {boolean}: The state to force into coil.

---

.writeCoils(address, array)

  Writes "Force Multiple Coils" (FC=15) request to serial port.

address {number}: The Data Address of the first register.

array {array}: The array of states to force into the coils.

---

.writeRegisters (address, array)

  Writes "Preset Multiple Registers" (FC=16) request to serial port.

address {number}: The Data Address of the first register.

array {array}: The array of values to set into the registers.

---

---

.writeRegister (address, value)

  Writes "Preset Single Register" (FC=6) request to serial port.

address {number}: The Data Address of the first register.

value {number}: The value to set into the register.

---

API Callbacks

---

This communication functions use callbacks.

// read 8 holding registers starting at register 10
// (function use the unit id 1)
client.writeFC3(1, 10, 8, function(err, data) {
      if (err) {
            console.log(err);
      } else {
            console.log(data);
      });

---

.open(callback)

  Opens a modbus connection using the given serial port.

callback {function}: (optional) Called when a connection has been opened.

---

.writeFC1 (unit, address, length, callback)

  Writes "Read coil status" (FC=01) request to serial port.

unit {number}: The slave unit address.

address {number}: The Data Address of the first register.

length {number}: The total number of registers requested.

callback {function}: (optional) Called once the unit returns an answer. The callback should be a function that looks like: function (error, data) { ... }

error - null on success, error string o/w
data - an object with two fildes:
    data.data: array of boolean coils (in multiples of 8 = one byte).
    data.buffer: raw baffer of bytes returned by slave.

---

.writeFC2 (unit, address, length, callback)

  Writes "Read input status" (FC=02) request to serial port.

unit {number}: The slave unit address.

address {number}: The Data Address of the first register.

length {number}: The total number of registers requested.

callback {function}: (optional) Called once the unit returns an answer. The callback should be a function that looks like: function (error, data) { ... }

error - null on success, error string o/w
data - an object with two fildes:
    data.data: array of boolean digital inputs (in multiples of 8 = one byte).
    data.buffer: raw baffer of bytes returned by slave.

---

.writeFC3 (unit, address, length, callback)

  Writes "Read Holding Registers" (FC=03) request to serial port.

unit {number}: The slave unit address.

address {number}: The Data Address of the first register.

length {number}: The total number of registers requested.

callback {function}: (optional) Called once the unit returns an answer. The callback should be a function that looks like: function (error, data) { ... }

error - null on success, error string o/w
data - an object with two fildes:
    data.data: array of unsinged 16 bit registers.
    data.buffer: raw baffer of bytes returned by slave.

---

.writeFC4 (unit, address, length, callback)

  Writes "Read Input Registers" (FC=04) request to serial port.

unit {number}: The slave unit address.

address {number}: The Data Address of the first register.

length {number}: The total number of registers requested.

callback {function}: (optional) Called once the unit returns an answer. The callback should be a function that looks like: function (error, data) { ... }

error - null on success, error string o/w
data - an object with two fildes:
    data.data: array of unsinged 16 bit registers.
    data.buffer: raw baffer of bytes returned by slave.

---

.writeFC5 (unit, address, state, callback)

  Writes "Force Single Coil" (FC=05) request to serial port.

unit {number}: The slave unit address.

address {number}: The Data Address of the first register.

state {boolean}: The coil state.

callback {function}: (optional) Called once the unit returns an answer. The callback should be a function that looks like: function (error, data) { ... }

---

.writeFC15 (unit, address, array, callback)

  Writes "Force Multiple Coils" (FC=15) request to serial port.

unit {number}: The slave unit address.

address {number}: The Data Address of the first register.

array {array}: The array of states to send to unit.

callback {function}: (optional) Called once the unit returns an answer. The callback should be a function that looks like: function (error, data) { ... }

---

.writeFC6 (unit, address, value, callback)

  Writes "Preset Single Register" (FC=6) request to serial port.

unit {number}: The slave unit address.

address {number}: The Data Address of the first register.

value {number}: The value to sent to unit.

callback {function}: (optional) Called once the unit returns an answer. The callback should be a function that looks like: function (error, data) { ... }

---

.writeFC16 (unit, address, array, callback)

  Writes "Preset Multiple Registers" (FC=16) request to serial port.

unit {number}: The slave unit address.

address {number}: The Data Address of the first register.

array {array}: The array of values to sent to unit.

callback {function}: (optional) Called once the unit returns an answer. The callback should be a function that looks like: function (error, data) { ... }

---

API connection shorthand

---

The shorthand connection functions creates a port and open it.

Long way, without shorthand:

// open a serial port
var SerialPort = require("serialport").SerialPort;
var serialPort = new SerialPort("/dev/ttyUSB0", {baudrate: 9600});

// create a modbus client using the serial port
var ModbusRTU = require("modbus-serial");
var client = new ModbusRTU(serialPort);

// open connection to a serial port
client.open();

// tell your coffee machine to do something ...

Using shorthand:

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

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

// tell your robot to do something ...

Using shorthand (TCP):

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

// open connection to a tcp line
client.connectTCP("192.168.1.42");

// tell your robot to do something ...

---

.connectRTU (path, options, callback)

  Connect using serial port.

path {string}: The port path (e.g. "/dev/ttyS0")

options {object}: (optional) The options for this connection.

callback {function}: (optional) Called once the client is connected.

---

.connectRTUBuffered (path, options, callback)

  Connect using buffered serial port.
  Use when serial port has long delays inside packets.

path {string}: The port path (e.g. "/dev/ttyS0")

options {object}: (optional) The options for this connection.

callback {function}: (optional) Called once the client is connected.

---

.connectTCP (ip, options, callback)

  Connect using tcp/ip.

ip {string}: The port ip (e.g. "24.230.1.42")

options {object}: (optional) The options for this connection.

callback {function}: (optional) Called once the client is connected.

---

.connectTelnet (ip, options, callback)

  Connect using a telnet server

ip {string}: The port ip (e.g. "24.230.1.42")

options {object}: (optional) The options for this connection.

callback {function}: (optional) Called once the client is connected.

---

.connectAsciiSerial (path, options, callback)

  Connect using serial port with ASCII encoding.

path {string}: The port path (e.g. "/dev/ttyS0")

options {object}: (optional) The options for this connection.

callback {function}: (optional) Called once the client is connected.