I want to get started using modbusClient in C# and visual studios to read the registers from a Seeed Studio TPH sensor that I linked below. I downloaded the manufacturers recommended application QModBus and followed the examples I found in the data sheet to set the COM port to COM 3, baud rate to 9600, data bits to 8, stop bits to 1, and parity to none.
Then I read from slave ID 1, function code 0x03 to read holding registers, start address 0 and number of coils 1 and I get a response of the temperature. This is all done in QModBus application.

Now I want to translate that to my C# code and display the temperature on a windows form. So far, I can connect to the COM port (COM3) and I think I am setting the initial parameters correctly.
I am not really sure how to set up the ModBus Request section and actually read the data from the register.

I think, in the method that I have called “buttonSendTest_Click” I want to set the Request data and read from the register, but I am unsure how exactly to set that up.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.IO.Ports;
using System.Threading;
 
namespace WindowsFormsApp1
{
    public partial class WeatherStation2 : Form
    {
        LPModBus modbusClient;
        private bool rloadConnected;
 
        public WeatherStation2()
        {
            InitializeComponent();
            modbusClient = new LPModBus();
            modbusClient.SetBaudRate(9600);
            modbusClient.SetCoilData(1);
            modbusClient.SetParity(System.IO.Ports.Parity.None);
            modbusClient.SetStopBits(System.IO.Ports.StopBits.One);
            modbusClient.SetUnitId(1);
            rloadConnected = false;
        }
 
 
        // Connect to the COM port
        private void buttonConnectCOM_Click(object sender, EventArgs e)
        {
            if (!rloadConnected)
            {
                string prt = Helpers.SafeGetComboSelectedText(comboBoxCOMport);
                if (prt != "")
                {
                    try
                    {
                        if (modbusClient.OpenModbusPort(prt))
                        {
                            Helpers.SafeSetLabeltext(labelStatus, "Connected");
                            rloadConnected = true;
                            Helpers.SafeSetButtontext(buttonConnectCOM, "Disconnect");
 
                        }
                    }
                    catch // (Exception ex)
                    {
                        rloadConnected = false;
                        Helpers.SafeSetButtontext(buttonConnectCOM, "Connect");
                        Helpers.SafeSetLabeltext(labelStatus, "Open Port Error");
                    }
                }
                else
                {
                    Helpers.SafeSetLabeltext(labelStatus, "Select comm port to continue");
                    rloadConnected = false;
                    Helpers.SafeSetButtontext(buttonConnectCOM, "Connect");
                }
            }
            else
            {
                Helpers.SafeSetButtontext(buttonConnectCOM, "Connect");
                modbusClient.ClosePort();
                rloadConnected = false;
                Helpers.SafeSetLabeltext(labelStatus, "Disconnected");
            }
        }
 
        //Here is where I want to read from the register and display it in a message box
        private void buttonSendTest_Click(object sender, EventArgs e)
        {
            modbusClient.SendReadHoldingRegisters();
            MessageBox.Show(modbusClient.ReadPortBytes(null, null).ToString());
 
 
        }
 
        // This method populates the COM ports combo box with all the detected COM ports. 
        private void comboBoxCOMport_Click(object sender, EventArgs e)
        {
            string[] PortNames = System.IO.Ports.SerialPort.GetPortNames();
            Helpers.SafetSetComboboxItmsClear(comboBoxCOMport);
            Helpers.SafeSetComboboxItems(comboBoxCOMport, PortNames);
        }
    }
}

https://www.seeedstudio.com/RS485-Air-Temperature-Humidity-and-Pressure-Sensor-p-5801.html[
QModBus Application Screenshot](https://i.sstatic.net/3aLqFLlD.png)

Ive tried writing the following code and reading from the holding register, but all I get is “System.Byte[]”. I am not sure what functions I need to call to read the register or whether I need to implement a time.sleep(), or any other useful tricks for the ModBus protocol.