Qserialdevice 2.0 waitForBytesWritten halfduplex question

[egadget1]

I have a question, writing a Qt GUI and I have the RTS line connected to a RS-485 driver transmit/receive control signal. I am sending out x number of bytes, I use the setRts(1) to make it go high (start of transmisson) and setRts(0) when I finish (as direction control). Does the waitForBytesWritten method work? I want it to wait until all the bytes have been transmitted out of the serial port, so I can setRts low. I see that sometimes the RTS signal is going low before all the bytes have been transferred. Any one have any ideas?

Do I have to set it up in unbuffered mode?

Here is a snippet of my code. Thanks in advance.

void TraceDialog::procSendButtonClick()
{
    QByteArray data;
    data.append(ui->lineEdit->text());
    m_port->setRts(1);
    if (data.size() > 0) {
        m_port->write(data);
        printTrace(data, false);
        ui->lbError->setText(QString::number(m_port->error()));
    }
    // Add in sleep timer
 
    while(m_port->waitForBytesWritten(15));  // Time out for 15 ms
 
    m_port->setRts(0);
}

void TraceDialog::procSendButtonClick()
{
    QByteArray data;
    data.append(ui->lineEdit->text());
    m_port->setRts(1);
    if (data.size() > 0) {
        m_port->write(data);
        printTrace(data, false);
        ui->lbError->setText(QString::number(m_port->error()));
    }
    // Add in sleep timer

    while(m_port->waitForBytesWritten(15));  // Time out for 15 ms

    m_port->setRts(0);
}

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