Hi guys, I need someone help to resolve my problem, I've created a program which connect with QtModbus via TCP to the server.
For prototype I use slave program created From qt which is connected on 127.0.0.1 port 502

with this code:
Qt Code: 
  1. modbusDevice = new QModbusTcpClient(this);
  2.     modbusDevice->setConnectionParameter(QModbusDevice::NetworkAddressParameter, "127.0.0.1");
  3.     modbusDevice->setConnectionParameter(QModbusDevice::NetworkPortParameter, 502);
  4.     if(!modbusDevice->connectDevice()){
  5.         ui->lbl_result->setText("Error");
  6.         return false;
  7.     }
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The program continue so I suppose that connection work

next I need to Read a register, for example Holding Register at address 1 inside the device so I code:

Qt Code: 
  1. QModbusDataUnit readUnit(QModbusDataUnit::HoldingRegisters, 1, 1);
  2.     if (auto *reply = modbusDevice->sendReadRequest(readUnit, 1)){
  3.         if (!reply->isFinished()){
  4.             connect(reply, &QModbusReply::finished, this, &MainWindow::show_result);
  5.         }else{
  6.             delete reply;
  7.         }
  8.     }else
  9.         ui->lbl_result->setText("Error");
  10.  
  11.     return true;
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and the show_result function is:

Qt Code: 
  1. void MainWindow::show_result(){
  2.     auto reply = qobject_cast<QModbusReply *>(sender());
  3.     if (!reply){
  4.         qDebug() << modbusDevice->errorString();
  5.         return;
  6.     }
  7.  
  8.     if (reply->error() == QModbusDevice::NoError){
  9.         const QModbusDataUnit unit = reply->result();
  10.         int startAddress = unit.startAddress();
  11.         int value = unit.value(0);
  12.         qDebug() << startAddress + " valore: " + value;
  13.     }
  14.     else
  15.         ui->lbl_result->setText("Error");
  16.  
  17.     reply->deleteLater();
  18. }
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But always when this function was called, return an error in the first line: "Device is not connected"

How I can fix this, I try to check all example or someting but i not find error.

Thanks for your help and attention