Weird behaviour when reading starting at odd and even addresses

[stefangeorgescu970]

G'day!

I am experiencing, as the title suggests, some weird behaviour when accessing registers from a PLC. As a disclaimer, there might be something extremely easy that I am missing, having close to no experience with this protocol.

The code I am using is the following

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

// open connection to a tcp line
client.connectTCP("localhost", { port: 20001 });
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);

When reading registers from address 0, the data received is the following:

[ 0, 0, 0, 0, 0, 0, 0, 16968, 0, 16968 ]

However, when reading from address 1, as opposed to the expected result (seeing the non zero values move to the left one place), we receive:

[ 0, 0, 0, 0, 16968, 0, 16968, 0, 0, 0 ]

When reading from address 2, the addressing is correct relative to reading from address 0:

[ 0, 0, 0, 0, 0, 16968, 0, 16968, 0, 0 ]

Reading from address 3 is correct relative to reading from address 1:

[ 0, 0, 16968, 0, 16968, 0, 0, 0, 0, 0 ]

This behaviour continues as we move forward through the addresses. I am using package version 8.0.9

Having searched through the issues I could not find anything, so my assumption is I am doing something wrong. Is it something completely wrong that I am doing? Could it be something related to the modbus server I am reading from?

[stefangeorgescu970]

Something that perhaps is worth mentioning about the code snippet setup. I use localhost since I have a TCP tunnel from my machine to the remote PLC.