### Install node-modbus-tcp via npm

Source: https://github.com/dresende/node-modbus-tcp/blob/master/Readme.md

Instructions to install the `modbus-tcp` library using npm. It's advised to consider `modbus-stream` for more complete functionality and broader protocol support (TCP, RTU, ASCII).

```sh
npm install modbus-tcp
```

--------------------------------

### Node.js Modbus TCP Client and Server Example

Source: https://github.com/dresende/node-modbus-tcp/blob/master/Readme.md

Demonstrates how to set up a Modbus TCP client and server using `node-modbus-tcp`, linking their streams for communication. It shows how to define a server event handler for 'read-coils' requests and how the client can initiate a 'readCoils' request, receiving the response via a callback.

```js
var modbus = require("modbus-tcp");
var client = new modbus.Client();
var server = new modbus.Server();

// link client and server streams together
client.writer().pipe(server.reader());
server.writer().pipe(client.reader());
// if you have a socket (stream) you can just
// call client.pipe(socket) or server.pipe(socket)

server.on("read-coils", function (from, to, reply) {
    return reply(null, [ 1, 0, 1, 1 ]);
});

// read coils from unit id = 0, from address 10 to 13
client.readCoils(0, 10, 13, function (err, coils) {
    // coils = [ 1, 0, 1, 1 ]
});
```

--------------------------------

### Modbus TCP Client Methods Reference

Source: https://github.com/dresende/node-modbus-tcp/blob/master/Readme.md

Lists the available methods on the `modbus.Client` object for reading and writing Modbus data. All read methods follow the signature `method(unitId, from, to, next)` and write methods follow `method(unitId, addr, val, next)`, where `next` is an optional callback. Addresses are 0-indexed, meaning 40001 in protocol refers to address 0.

```APIDOC
Client Methods:
- readCoils(unitId: number, from: number, to: number, next?: Function)
- readDiscreteInputs(unitId: number, from: number, to: number, next?: Function)
- readHoldingRegisters(unitId: number, from: number, to: number, next?: Function)
- readInputRegisters(unitId: number, from: number, to: number, next?: Function)
- writeSingleCoil(unitId: number, addr: number, val: number, next?: Function)
- writeSingleRegister(unitId: number, addr: number, val: number, next?: Function)
- writeMultipleCoils(unitId: number, addr: number, val: number, next?: Function)
- writeMultipleRegisters(unitId: number, addr: number, val: number, next?: Function)

Parameters:
  unitId: The Modbus unit identifier.
  from: The starting address for read operations.
  to: The ending address for read operations.
  addr: The address for write operations.
  val: The value to write.
  next: An optional callback function (err, result) called upon server reply.
```

--------------------------------

### Modbus TCP Server Events Reference

Source: https://github.com/dresende/node-modbus-tcp/blob/master/Readme.md

Lists the events emitted by the `modbus.Server` object when Modbus function codes are received. These events correspond to standard Modbus operations. The `data` event is a special case, triggered when an unknown function code is received by the server.

```APIDOC
Server Events:
- read-coils
- read-discrete-inputs
- read-holding-registers
- read-input-registers
- write-single-coil
- write-single-register
- write-multiple-coils
- write-multiple-registers
- data: Triggered when an unknown function code is received.
```

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