modbus-tcp-client

ModbusClient

ModbusClient manages connection and fetches data based on provided layout of modbus regusters and coils.

const ModbusClient = require('modbus-tcp-client');

const layout = ModbusClient.ModbusLayout.fromFile('./layout.json');
const host = 'localhost';
const port = 502;

const client = new ModbusClient(host, port, layout);

client.open();

client.on('open', () => client.update());
client.on('close', () => console.log('client closed'));
client.on('update', (layout) => console.log(layout));
client.on('error', (err) => console.error(err));

ModbusLayout

ModbusLayout class describes location and type of data stored on modbus registers and coils.

coils and discrete arrays should consist of objects containing field address. descrete and holding arrays should consist of objects containing fields address and type (available types are listed below). If type is omitted, uint16 is assumed.

In addition all objects can contain props property which will be attached to ModbusCoil and ModbusRegister objects created by ModbusLayout.

const ModbusLayout = require('modbus-tcp-client').ModbusLayout;

const layout1 = ModbusLayout.fromFile('./layout.json');

const layout2 = new ModbusLayout({
  coils: [ { address: 0 }, { address: 1 } ],
  discrete: [ { address: 10000 }, { address: 10001 } ],
  input: [ { address: 30000, type: 'uint16' } ],
  holding: [ { address: 40000, type: 'uint32' } ],
});

Example modbus layout file:

{
  "coils": [
    {
      "address": 0,
      "props": {
        "name": "Coil 1",
      }
    }, {
      "address": 1,
      "props": {
        "name": "Coil 2",
        "description": "Description of second coil",
      }
    }
  ],

  "discrete": [
    {
      "address": 10000,
      "props": {
        "name": "Discrete 1",
      }
    }, {
      "address": 10001,
    }
  ],

  "input": [
    {
      "address": 30000,
      "type": "string16",
      "props": {
        "name": "Name",
      }
    }, {
      "address": 30008,
      "type": "uint32",
      "props": {
        "name": "Age",
      }
    }
  ],

  "holding": [
    {
      "address": 40000,
      "type": "uint16",
      "props": {
        "name": "IP",
      }
    }
  ]
}

Available types

Following register types are supported:

| identifier | description | |-|-| | int16 | 16 bit integer (2 bytes / 1 word) | | int32 | 32 bit integer (4 bytes / 2 words) | | int64 | 64 bit integer (8 bytes / 4 words) | | uint16 | 16 bit unsigned integer (2 bytes / 1 word) | | uint32 | 32 bit unsigned integer (4 bytes / 2 words) | | uint64 | 64 bit unsigned integer (8 bytes / 4 words) | | float | single precision floating point number (4 bytes / 2 words) | | double | double precision floating point number (8 bytes / 4 words) | | stringX | string of specified byte length, where X is the number of bytes |