QModbus long frame transmission error

[Hy Tang]

I use a USB-to-RS485 converter, send request frame with write a small number of registers(such as 5 registers), it is ok, but with a large number of registers(such as 60 registers), it can not work well.

Environment:
Windows 7
Qt 5.10.0
MinGW 32bit

Repetition:
I use a spinBox to choose number of register, and a button to send Modbus request.

void MainWindow::on_pushButtonSend_clicked()
{
    int reg = ui->spinBoxReg->value();
    if (auto *reply = mClient->sendWriteRequest(QModbusDataUnit(QModbusDataUnit::HoldingRegisters, 0, reg), 1)) {
        if (!reply->isFinished()) {
            connect(reply, &QModbusReply::finished, this, [this, reply]() {
                if (reply->error() == QModbusDevice::ProtocolError) {
                    statusBar()->showMessage(tr("Write response error: %1 (Modbus exception: 0x%2)")
                                             .arg(reply->errorString()).arg(reply->rawResult().exceptionCode(), -1, 16));
                } else if (reply->error() != QModbusDevice::NoError) {
                    statusBar()->showMessage(tr("Write response error: %1 (code: 0x%2)")
                                             .arg(reply->errorString()).arg(reply->error(), -1, 16));
                } else {
                    statusBar()->showMessage(tr("Write ok"));
                }
                reply->deleteLater();
            });
        } else {
            reply->deleteLater();
        }
    } else {
        ui->statusBar->showMessage(tr("Write error: ") + mClient->errorString());
    }
}

and the initialize:

    mClient = new QModbusRtuSerialMaster;
    mClient->setConnectionParameter(QModbusDevice::SerialPortNameParameter, "COM3");
    mClient->setConnectionParameter(QModbusDevice::SerialBaudRateParameter, 9600);
    mClient->setConnectionParameter(QModbusDevice::SerialParityParameter, QSerialPort::NoParity);
    mClient->setConnectionParameter(QModbusDevice::SerialDataBitsParameter, QSerialPort::Data8);
    mClient->setConnectionParameter(QModbusDevice::SerialStopBitsParameter, QSerialPort::OneStop);
    mClient->setTimeout(3000);
    mClient->setNumberOfRetries(2);
    if (!mClient->connectDevice()) {
        QMessageBox::information(this, tr("err"), tr("can not open"));
        delete mClient;
        mClient = nullptr;
        ui->pushButtonSend->setEnabled(false);
    } else {
        ui->pushButtonSend->setEnabled(true);
    }

the log info:

[jsulm]

@Hy-Tang You will need to provide more information if you want to get meaningful answer.
"it can not work well" - this is not a problem description...

[J.Hilk]

@Hy-Tang does your device even accept such long frames ? How does it handle, for example, access tries of invalid registers. Is the Modbus Exception implemented correctly ?

are you really only sending 60 Registers ?

MODBUS only allows to READ 125 and WRITE 123 Registers in one datagram. aka 256 byte are you sure you'r not exceeding this ?

[Hy Tang]

@jsulm I posted the problem in advance due to misoperation, and have added the details

[Hy Tang]

@J-Hilk I use Modbus Slave (https://modbustools.com/modbus_slave.html) to test this question, in modbus slave's Communication Traffic window, it has receive the long frame, and send the response, but qt client has error information.