PLCLink

A library that "links" node and real PLC infrastructure.

Installation

Run the following command in the root of your directory

npm install plclink

Quick Start

Save a new PLC Device with

import PLC from 'plclink';

const plc = new PLC({ host: "[Your PLC's IP]", port: 502 })

[Required] Then connect to it using

await plc.connect()

After that you can pretty much use simple commands to read/write from the PLC

Examples

Read the value of the holding register "1" and write "54" to the holding register "2":

import PLC from 'plclink';

const plc = new PLC({ host: "[Your PLC's IP]", port: 502 })
await plc.connect()

const ValueOf1 = await plc.read(1)
await plc.write(2, 54)

console.log(ValueOf1)

Set the coil "5" to false/0 and read multiple input registers:

import PLC from 'plclink';

const plc = new PLC({ host: "[Your PLC's IP]", port: 502 })
await plc.connect()
await plc.writeCoil(5, false)

const Values = await plc.readInputs([1,23,65,98])
console.log(Values)

Read discrete inputs and check their values:

import PLC from 'plclink';

const plc = new PLC({ host: "[Your PLC's IP]", port: 502 })
await plc.connect()

const inputs = await plc.readDiscreteInputs([1, 2, 3, 4])
console.log(inputs)

Read coil states from a machine and log which ones are active:

import PLC from 'plclink';

const plc = new PLC({ host: "[Your PLC's IP]", port: 502 })
await plc.connect()

const coils = await plc.readCoils([1, 2, 3])
for (const [address, result] of Object.entries(coils)) {
    console.log(`Coil ${address}: ${result.AddressValues[0] ? 'ON' : 'OFF'}`)
}

Using the Watcher (New in v2)

Monitor specific registers and react only when the value changes:

import PLC from 'plclink';

const plc = new PLC({ host: "127.0.0.1" });
await plc.connect();

// Watch registers 1, 5, and 10 every 500ms
const watcher = await plc.watch([1, 5, 10], (changes) => {
    console.log("Changes detected!");
    for (const [address, data] of Object.entries(changes)) {
        console.log(`Address ${address} went from ${data.PrevValue} to ${data.Value}`);
    }
}, 500);

// You can manage the stream without destroying the interval
watcher.pause();
watcher.resume();

watcher.stop();

Supported Protocols

• Modbus TCP
• S7 (Soon)
• EtherNet/IP (Soon)
• (More coming in later versions)

API reference

new PLC(options)

| Option | Type | Default | Description | |--------|------|---------|-------------| | host | string | required | The IP address of the PLC | | port | number | 502 | The port to connect to | | unit | number | 1 | The unit ID of the PLC | | protocol | string | "modbus" | The protocol to use |

plc.connect()

Connects to the PLC. Must be awaited before any read/write calls.

plc.read(registers)

Reads holding register values. Accepts a single address or array of addresses.

plc.readInputs(registers)

Reads input register values. Read-only. Accepts a single address or array of addresses.

plc.readCoils(coils)

Reads coil values. Accepts a single address or array of addresses.

plc.readDiscreteInputs(discreteInputs)

Reads discrete input values. Read-only. Accepts a single address or array of addresses.

plc.write(register, value)

Writes a number to a holding register.

plc.writeCoil(coil, value)

Writes a boolean or 0xFF00/0x0000 to a coil.

plc.watch(registers, callback, interval)

Fires callback every time the specified Holding Registers change value.

plc.watchInputs(registers, callback, interval)

Fires callback every time the specified Input Registers change value.

plc.watchCoils(coils, callback, interval)

Fires callback every time the specified Coils change state.

plc.watchDiscreteInputs(discreteInputs, callback, interval)

Fires callback every time the specified Discrete Inputs change state.

Watcher Instance

| Method | Description | |--------|-------------| | .pause() | Stops firing the callback but keeps polling the PLC. | | .resume() | Resumes firing the callback when changes are detected. | | .stop() | Clears the interval and stops the watcher completely. |

Created and distributed by Cozen10 (Anastasios Fountoglou)