QT and USB Modbus comunication

[tbscope]

QExtSerialPort is not intended for USB.

You need a driver that exposes an api that you can use to get the data from the USB port
Any website about hobby electronics probably has a link to such a driver.

Then you need to use that api and implement the modbus protocol.

[hruodbert]

Thank for your reply

But I want put the data on USB port. I do use a driver that exposes an api also for put the data or that solution it's valid only for get the data from the USB port?

[tbscope]

I guess most drivers can send and receive.
http://sourceforge.net/apps/trac/libusb-win32/wiki

You can also buy ready made solutions (read: a modbus driver)

[marcvanriet]

Hello,

Modbus is just a serial protocol using RS485 (something similar to the RS232 port on your desktop computer).

You can use QExtSerialport (it's on sourceforge I think) for the serial communication.

You can use an USB-to-RS485 convertor to communicate on the RS485 bus (you can buy it on Newark or Digikey or in your computer shop).
This kind of converter acts like a serial port, so you don't have to know anything about USB.

And then you have to implement the Modbus protocol (that is, send the correct data packets on the bus and handle the incoming data packets).
I believe there is an open-source implementation of Modbus that can get you started for implementing the protocol.

If you get this to work, give me a signal. I can use it too

Best regards,
Marc

[HM]

Have a look at pvbrowser http://pvbrowser.de/pvbrowser/index.php - They have implemented Modbus RTU via USB and other protocolls.