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binary data communication through SerialPort

  • Hi,

    I am a newbie working on Qt to get data through Serial Port, trying to talk to CY5670, Cypree Dongle.

    It seems like, QSerialPort Class cannot talk to it with binary communication very well that, I cannot get any data.

    Is there a way that Qt may work like RealTerm/IIRC to communicate through binary data via serial port?

    Thank you!

  • QSerialPort is what you need. Have you got the dongle protocol?

  • Lifetime Qt Champion

    hi besides what @mrdebug ask, have you tested wtih
    Its available directly in Creator and good for testing.

  • Hi @mrdebug @mrjj ,

    That Terminal example is exactly what I have tried, and then I got the conclusion that QSerialPort Class cannot talk to it; I assume that is because of the failure of binary communication, however not sure about it.

    All I know is, serialRead() was never activated even though serialWrite() has been gone through again and again.

    Here is cited by Cypress Forum about CY5670 dongle communication:
    "Since the communication uses binary codes Putty is propably not the right tool. Maybe use RealTerm, IIRC it has a mode the send and receive binary data. And I think you need to send the correct data to the dongle to answer. Maybe there is some command sequence to get a version number?"

    It is sure that Putty could not talk to the dongle, while QSerialPort is similar to Putty.

    Could anyone help me find a solution to talk to the CY5670 dongle?

    Thank you!

  • Every comms in serial is basically binary. It will not know a difference.
    In most cases it is a baud rate respectively other settings issue. I guess that is also the issue with Putty.
    Do you have the correct baud rate, data and stop bits and otzher flags?

  • Lifetime Qt Champion

    Im not sure what you mean by binary communication.
    But QSerialPort can handle all that a com port can send.

    When data comes in Terminal Example
    Its read into a byte array which can handle binary just fine.
    But the PutData calls

    And if its not printable as text, it might become nothing. (shows nothing)

    So first check is to see if readData() is called.

    If dongle has protocol, it might expect you to send something to it before it
    sends anything.

    void MainWindow::readData()
    QByteArray data = serial->readAll();
    qDebug() << "Its alive"; /// to test its called

  • @koahnig said:

    Do you have the correct baud rate, data and stop bits and otzher flags?

    Yes, I am sure those are correct.

    The dongle is controlled by command packets. And any wrong command packets should active a error response, which I never received; the serialRead() was never called.

  • Lifetime Qt Champion

    well I would try with then and see if it even works at all.

  • Have you tried the QThread approach instead of events?
    Please, download this
    and have a look at the file qthcomport.cpp
    I know everybody don't like the QThread approach instead of events but in a difficoult situation I think the QThread approach is better. You can manage timemouts an polling.
    Have you got the dongle serial protocol?
    Every serial device has a protocol. For example if you send at a modem at&v you will have the current modem configuration.
    Often the serial devices have a command to know the firmware version. This is the first command to implement. Normally there are a byte to begin, end and control.
    Have you found the serial protocol in the sdk?

  • Lifetime Qt Champion


    Maybe a silly question but are you sure this dongle can be used like a serial port ? The description says BLE to USB bridge.

  • I think the same thing. I normally use ble with bluez ( the Debian bluetooth stack) and not the usb dongle directly. Maybe his usb dongle has the bluetooth stack embedded.

  • Hi @mrjj @mrdebug ,

    Thank you guys for helping me.

    I finally got a response after sending a command packet to the dongle through a serial port.

    So happy about it!

  • Lifetime Qt Champion


  • Lifetime Qt Champion

    Nice, what was the problem ?

    On a side note, you don't need to modify your thread title anymore, just use the "Topic Tool" button to mark the thread as solved :)

  • That CY5670 BLE dongle discards any commands without a header, which means I need to add a header to my command packet to talk to the dongle, otherwise nothing will happen.

  • Lifetime Qt Champion

    Thanks for sharing your findings :)

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