modbus

A simple interface for Modbus

• Read and write modbus registers
• One interface for both RTU and TCP
• Support for promises and callbacks

Quick Example

const modbus = require('modbus')

//Create a TCP Device
const device = modbus(ipAddress,port,unitId) 

//Create an RTU Device
const device = modbus(commPort,baudRate)

//Read
let myCoil = await device.read('c0')
let myHoldingRegister = await device.read('hr0') 
let myHoldingRegisters = await device.read('hr1-2') 

//Write
await device.write('c0',true)
await device.write('hr0',15)

Device Object

Constructor

const modbus = require('modbus')
const tcpDevice = modbus(ipAddress,port,unitId)

Properties

• ipAddress
• port
• unitId
• timeout
• online

Methods

read(address,[callback])

• address - Coil or register to read.
• callback(err,res) - Optional.

write(address,value,[callback])

• address - Coil or register to read.
• value - Data to write.
• callback(err,res) - Optional.

Address Syntax

[Short Hand + Register Number]

i.e.

• 'i8' - Descrite Input 8
• 'hr418' - Holding Register 418
• 'hr418-419' - Holding Registers 418 through 419

Applicable Datatypes

Data Type                  Short Hand   Size        Accessibility     
Descrite Input             i            1 Bit       Read Only
Coil                       c            1 Bit       Read / Write
Input Register             ir           16 Bits     Read Only
Holding Register           hr           16 Bits     Read / Write

Implemented Function Codes

• FC1 - Read Coil
• FC2 - Read Input
• FC3 - Read Holding Registers
• FC4 - Read Input Registers
• FC5 - Write Single Coil
• FC6 - Write Single Register
• FC15 - Write Multiple Coils
• FC16 - Write Multiple Registers

Recompile for Electron

If modbus is not compiled for the correct version of Node.js, you will not be able to communicate via Modbus RTU. (Modbus TCP is not affected)

When you install modbus it will compile against the version of Node.js on your machine, not against the Node.js runtime bundled with Electron.

To recompile modbus (or any native Node.js module) for Electron, you can use electron-rebuild

Install modbus:

npm i modbus

Install electron-rebuild with --save-dev:

npm install --save-dev electron-rebuild

Run electron-rebuild:

$(npm bin)/electron-rebuild

Or if you're on Windows:

.\node_modules\.bin\electron-rebuild.cmd