Write to Slave in modbus

rezaMSLM

Hi
I want to change slave ID In modbus, current slave ID is 3 and i want to change it to 4;
the ID is stored in address 3 of holding registers; I use this code but doesn't work:

void MainWindow::on_pushButton_WriteID_clicked()
{
    QModbusDataUnit writeUnit = QModbusDataUnit(QModbusDataUnit::HoldingRegisters) ;//specify register type
    writeUnit.setStartAddress(3);//set start address
    writeUnit.setValueCount(1);//set number of data blocks
    writeUnit.setValue(0,4);//set value 4 in index 0 (new slave ID)

    if(auto *reply = ModbusObject->sendWriteRequest(writeUnit,/*device slave ID:*/ 3))//send data unit to slave ID 3
    {
        if(!reply->isFinished()){
            connect(reply,&QModbusReply::finished,this,MainWindow::WriteID);
            qDebug()<<"ok";
        }

        else{
            statusBar()->showMessage("error!",2000);
            delete reply;
        }
    }
    else
        statusBar()->showMessage("error!",2000);
}

void MainWindow::WriteID()
{

    auto reply = qobject_cast<QModbusReply *>(sender());
    if (!reply){
        qDebug()<<"returned";
        return;
    }

    if(reply->error()){
        statusBar()->showMessage(tr("ERROR:%1").arg(reply->errorString()),2000);
    }
    else{
        statusBar()->showMessage("Write Successful!",2000);
    }
    reply->deleteLater();

}

when I Click on Write button "Write successful" is printed but the ID is not changed.

dheerendra

It is good idea to look at modbus slave side for troubleshooting this issue.

rezaMSLM

modifying writeUnit like this also doesn't work:

    auto writeUnit = QModbusDataUnit(QModbusDataUnit::HoldingRegisters
                                     ,/*address*/3,/*new value*/4);
/*
  writeUnit.setStartAddress(3);//set start address
  writeUnit.setValueCount(1);//set number of data blocks
  writeUnit.setValue(2,4);//set value 4 in index 0 (new slave ID)
*/

rezaMSLM

This post is deleted!