Modbusjs NPM | npm.io

ModbusJS

Overview

Modbus communication library for NodeJS using promises.

Status

The library is under active development and i keep adding functionality as well as possibly changing already implemented functionality if required. However i'll try to keep already implemented and working interfaces unchanged.

Currently implemented and working functionality :

ModbusTcpClient - Modbus client (master) for communication over TCP
- readCoils
- readDiscreteInputs
- readHoldingRegisters
- readInputRegisters
- writeSingleCoil
- writeSingleRegister
- writeMultipleCoils
- writeMultipleCoilsSameValue
- writeMultipleRegisters
- writeMultipleRegistersSameValue

Installation

npm install modbusjs

Usage

ModbusJS is using ES6 Promises (thus no 3rd party promise module dependency) to handle read/write requests. On top of that events are implemented as well for connection handling.

ModbusTcpClient

var ModbusTcpClient = require('modbusjs').ModbusTcpClient;

constructor

Returns a new instance of ModbusTcpClient. Connection is not established at this point.

function(host, port,options)

host: IP address or DNS name of modbus server
port: Port of modbus server (usually 502)
options: Optional
- debug: Turn on debugging messages printed out to console. Default value is FALSE.
- autoReconnect: Automatic reconnect in case connection is lost. Default value is FALSE.
- autoReconnectInterval: Interval before trying to reconnect in seconds. Default values is 10.

example

var modbusTcpClient = new ModbusTcpClient('localhost', 502, {debug: true, autoReconnect: true, autoReconnectInterval: 5})

connect

Tries to establish communication with target modbus server. Triggers error event in case of error and connect if successful.

example

modbusTcpClient.connect().then(function(){
    // Success
}).catch(function(err){
    // Error
});

disconnect

Destroys TCP socket if active and runs several clean up procedures. Triggers disconnect event if successful.

example

modbusTcpClient.disconnect().then(function(){
    // Success
}).catch(function(err){
    // Error (ie. no active connection)
});

reconnect

Tries to reconnect to target modbus server. Triggers reconnect event if successful.

example

modbusTcpClient.reconnect().then(function(){
    // Success
}).catch(function(err){
    // Error
});

isConnected

Returns current connection status.

var connectionStatus = modbusTcpClient.isConnected();

readCoils

Reads coils from the modbus server. Maximum number of coils which can be read in one transaction is 2000.

function(address, length,options)

Input parameters

address: Starting coil address
length: Number of coils to read
options: Optional
- timeout: Request timeout. Default value is 5 seconds.

Result

result: Array of booleans
request: Request object
response: Response object

example

modbusTcpClient.readCoils(0, 10).then(function(result){
    // Success
}).catch(function(err){
    // Error
});

readDiscreteInputs

Reads inputs from the modbus server. Same interface and return values as readCoils.

example

modbusTcpClient.readDiscreteInputs(0, 10).then(function(result){
    /// Success
}).catch(function(err){
    // Error
});

readHoldingRegisters

Reads holding registers from modbus server. Maximum number of registers which can be read in one transaction is 125.

function(address, length,options)

Input parameters

address: Starting register address
length: Number of registers to read
options: Optional
- timeout: Request timeout. Default is 5 seconds.
- unsigned: By default all the results are read as signed. If this options is TRUE then unsigned conversion will be used instead.

Result

result: Array of (U)Int16
request: Request object
response: Response object

example

modbusTcpClient.readHoldingRegisters(0, 10).then(function(result){
    // Success
}).catch(function(err){
    // Error
});

readInputgRegisters

Reads input registers from the modbus server. Same interface and return values as readHoldingRegisters.

example

modbusTcpClient.readInputgRegisters(0, 10).then(function(result){
    // Success
}).catch(function(err){
    // Error
});

writeSingleCoil

Writes single coil value.

function(address, value,options)

Input parameters

address: Coil address
value: Valid values are true/false and 1/0
options: Optional
- timeout: Request timeout. Default is 5 seconds.

Result

result: Echoed value from the request
request: Request object
response: Response object

example

modbusTcpClient.writeSingleCoil(6, 0).then(function(res){
    // Success
}).catch(function(err){
    // Error
})

writeSingleRegister

Writes single register value.

function(address, value,options)

Input parameters

address: Register address
value: Maximum value is 0xFFFF.
options: Optional
- timeout: Request timeout. Default is 5 seconds.

Result

result: Echoed value from the request
request: Request object
response: Response object

example

modbusTcpClient.writeSingleRegister(1, 123).then(function(res){
    // Success
}).catch(function(err){
    // Error
})

writeMultipleCoils

Writes multiple coils in one transaction.

function(address, values,options)

Input parameters

address: Starting coil address
values: Array of booleans (or 0/1) to be written to the server starting from starting address.
options: Optional
- timeout: Request timeout. Default is 5 seconds.

Result

result: Number of updated output coils
request: Request object
response: Response object

example

modbusTcpClient.writeMultipleCoils(1, [true, false, false, true, 0, 0, 1]).then(function(res){
    // Success
}).catch(function(err){
    // Error
})

writeMultipleCoilsSameValue

Just a helper with a same functionality as writeMultipleCoils providing function for cases when the value is same for the whole bulk of coils.

function(address, length, value,options)

Input parameters

address: Starting coil address
length: Number of coils to be updated
value: Boolean (or 0/1) value to be written to address, address + length interval.
options: Optional
- timeout: Request timeout. Default value is 5 seconds.

Result

result: Number of updated output coils
request: Request object
response: Response object

example

modbusTcpClient.writeMultipleCoilsSameValue(1, 20, true).then(function(res){
    // Success
}).catch(function(err){
    // Error
})

writeMultipleRegisters

Writes multiple registers in one transaction.

function(address, values,options)

Input parameters

address: Starting register address
values: Array of UInt16 to be written to the server starting from the starting address.
options: Optional
- timeout: Request timeout. Default is 5 seconds.

Result

result: Number of output registers
request: Request object
response: Response object

example

modbusTcpClient.writeMultipleRegisters(1, [1,2,3,4,5,6,7,8]).then(function(res){
    // Success
}).catch(function(err){
    // Error
})

writeMultipleRegistersSameValue

Just a helper with a same functionality as writeMultipleRegisters providing function for cases when the value is same for the whole bulk of registers.

function(address, length, value,options)

Input parameters

address: Starting register address
length: Number of registers affected
value: UInt16 value to be written to address, address + interval.
options: Optional
- timeout: Request timeout. Default is 5 seconds.

Result

result: Number of output registers
request: Request object
response: Response object

example

modbusTcpClient.writeMultipleRegistersSameValue(1, 20, 666).then(function(res){
    // Success
}).catch(function(err){
    // Error
})

Events

connect

Emitted when successfully connected to the modbus server.

modbusTcpClient.on('connect', function(err){
    console.log('CONNECTED - EVENT');
});

error

Emitted when network (socket) error occurs.

modbusTcpClient.on('error', function(err){
    console.log('ERROR - ' + err);
});

disconnect

Emitted when the connection is lost. (not emitted during reconnection)

modbusTcpClient.on('disconnect', function(){
    console.log('DISCONNECTED - EVENT');
});

reconnect

Emitted when successfully reconnected to the modbus server

modbusTcpClient.on('disconnect', function(){
    console.log('DISCONNECTED - EVENT');
});

Examples

All the examples can be found in examples folder or above per individual functions.

Examples can triggered via npm however IP address of modbus server might have to be modified directly in the file (default localhost)

npm run [example-name]

nodejs modbus plc automation

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