<![CDATA[How to set QSerialPort::PinoutFlags and XonLimit/XoffLimit values?]]>@QSerialPort port(port_info.name);
if (port.open(QIODevice::ReadWrite)) {
port.setParity(port_info.parity); //QSerialPort::NoParity
port.setFlowControl(port_info.flow); //QSerialPort::SoftwareControl
port.setBaudRate(port_info.baud_rate, //QSerialPort::Baud19200
QSerialPort::AllDirections);
port.setDataBits(port_info.data_bits); //QSerialPort::Data8
port.setStopBits(port_info.stop_bits); //QSerialPort::OneStop
port.setReadBufferSize(port_info.read_buffer); //8
port.setDataTerminalReady(port_info.data_terminal_ready); //true
port.setRequestToSend(port_info.request_to_send); //false
if (port.isReadable() && port.isWritable()) {
qDebug() << port.pinoutSignals();
if (port.error() != QSerialPort::NoError) {
qDebug() << port.errorString();
}
else {
forever {
if (!allowed_to_work) {
break;
}
else {
readLoop(port);
writeOnceIfNeeded(port);
}
}
}
}
}
port.close();@

This skel code of mine is working for many different sets of QSerialPort's properties; I can freely read from and write to some devices I'm using it with. Now I'm trying to use it with new hardware and it needs to be configured in a way I don't know how to bite.

The above code returns no errors but also no PinoutFlags. I want my port.pingoutFlags() to return (0x80|0x40) (QSerialPort::ClearToSendSignal, DTS) but:

I would expect the above example to return (0x40) (DTS only, no RTS) while it's returning no flags,

I don't know how to set CTS variable because I can't find method similar to those to set DTS and RTS values,

I found some weird output when playing with setRequestToSend() and setDataTerminalReady() methods:

  • If I set RTS to true then I'm getting (0x40) (RTS only, no DTS) no matter if I'm setting DTS to true or to false,
  • if I set RTS only, I end up with (0x4|0x40) (RTS and DTR on);
  • etc. but the isDataTerminalReady() and isRequestToSend() methods return predictable values, different than these viewable by pinoutSignals();

Using Device Monitoring Studio I can see that the values of PinoutSignals count as "FlowReplace", not values returned by above mentioned methods - that's why I'm looking for the way to change them directly... but pinoutSignals() returns no reference, only a copy so I can't just use operator|= and hope for the best.

Also, I can't figure the way to set XonLimit and XoffLimit values...

]]>https://forum.qt.io/topic/48371/how-to-set-qserialport-pinoutflags-and-xonlimit-xofflimit-valuesRSS for NodeSat, 25 Apr 2026 12:51:04 GMTThu, 20 Nov 2014 15:38:05 GMT60<![CDATA[Reply to How to set QSerialPort::PinoutFlags and XonLimit/XoffLimit values? on Thu, 20 Nov 2014 17:55:29 GMT]]>
  • Windows, yes. Device is home-made so I don't think it has a "type"...
  • They are. There were "if jungle" there but I've deleted the checks before posting to make it more clear to you. Btw. isn't " if (port.error() != QSerialPort::NoError)" enough?
  • I think I get all these flags wrong. I just deleted the part of code which was trying to set them and now everything is working... sorry for garbage topic.
    • ]]>    https://forum.qt.io/post/251733https://forum.qt.io/post/251733Thu, 20 Nov 2014 17:55:29 GMT    <![CDATA[Reply to How to set QSerialPort::PinoutFlags and XonLimit/XoffLimit values? on Thu, 20 Nov 2014 17:09:02 GMT]]>
  • Please provide info about your OS and device type.
  • Please check that all setXX() methods returns true!

    • [quote]
    I would expect the above example to return (0×40) (DTS only, no RTS) while it’s returning no flags,
    [/quote]

    Why do you expect it?

    [quote]
    I don’t know how to set CTS variable because I can’t find method similar to those to set DTS and RTS values,
    [/quote]

    Is is impossible, since CTS is an input line.

    [quote]
    bq. If I set RTS to true then I’m getting (0×40) (RTS only, no DTS) no matter if I’m setting DTS to true or to false,
    [/quote]

    How you did " setting DTS to true or to false" ?

    [quote]
    etc. but the isDataTerminalReady() and isRequestToSend() methods return predictable values, different than these viewable by pinoutSignals();
    [/quote]

    the isDataTerminalReady() and isRequestToSend() implicitly calls of pinoutSignals() to query a desired bit.

    [quote]
    that’s why I’m looking for the way to change them directly…
    [/quote]

    You can change only RTS and DTR signals, since it is outgoing signals..

    [quote]
    Also, I can’t figure the way to set XonLimit and XoffLimit values…
    [/quote]

    This is a platform-specific thing (I suppose you talk about Windows). So you can use QSerialPort::handle() -> query the DCB -> change what you want -> update DCB.

    ]]>    https://forum.qt.io/post/251730https://forum.qt.io/post/251730Thu, 20 Nov 2014 17:09:02 GMT