Unable to connect TCP

[piyushparag]

Hi. I tried the code as it is mentioned in the example:

// create an empty modbus client const ModbusRTU = require("modbus-serial"); const client = new ModbusRTU();

// open connection to a tcp line client.connectTCP("127.0.0.1", { port: 8502 }); client.setID(1);

// read the values of 10 registers starting at address 0 // on device number 1. and log the values to the console. setInterval(function() { client.readHoldingRegisters(0, 10, function(err, data) { console.log(data.data); }); }, 1000);

But, I am unable to get a connection with TCP. When I try running the code, I get the following error:

node:internal/process/promises:288 triggerUncaughtException(err, true /* fromPromise */); ^

Error: connect ECONNREFUSED 127.0.0.1:8502 at TCPConnectWrap.afterConnect [as oncomplete] (node:net:1237:16) { errno: -4078, code: 'ECONNREFUSED', syscall: 'connect', address: '127.0.0.1', port: 8502 }

Node.js v18.5.0

I have tried doing this with different versions of nodejs but I am getting the same result everytime. Can you please help me? The code worked just once yesterday and I have been trying to make it work again since but have been unsuccessful. Please help.

[saguado69]

I recommend you to wrap setIntercal in a function and call this after TCP connection is done.

ECONNREFUSED means the host is not reachable, I suggest you to check first with ModPoll, or any modbus tool.

async function modbusConnect() {
    await client.connectTCP(hostAddress, hostPort)
        .then(() => {
            if (client.isOpen) {
                console.log(`Polling Modbus → IP: ${hostAddress} /PORT ${hostPort.port}`);
                pollModbusDevices(3000);
            }
        })
        .catch(err => {
            if (err.code == 'ETIMEDOUT' || err.errno == 'ECONNREFUSED') {
                if (intervalId) {
                    clearInterval(intervalId);
                }
                modbusConnect();
            }
            console.log(err.message);
        });
}

// Read registers values starting at address 0
// on all nodes (nodeIds), and show values to console
function pollModbusDevices(interval) {
    intervalId = setInterval(function () {
        for (let node of nodeIds) {
            client.setID(node);
            client.readHoldingRegisters(0, 100, function (err, data) {
                if (data) {
                   // do whatever ...
                }
                if (err) {
                    console.log(err.message);
                    if (err.errno == 'ECONNREFUSED') {
                        client.close();
                        modbusConnect();
                    }
                }
            });
        }
    }, interval);

}