Modbus_Serial

[c77asper]

Hey :)
I am working on a school project, but it seems to be a bigger project than expected because of QT :)
I made a board, that can turn off and on some resistors in parallel, and give a specific value on my output.
I use modbus poll to write to my board (there is a STM32 microprocessor on the board) to set the value i want.

The problem is, i need a GUI interface, but it has to be simple.
The user just need to choice the COM port, all the settings with baud rate, stop bits etc. is already predefined.
After the user has selected the COM port, the user just need to write a resistance he wants, and that's all.
It is function code 6 (Write single register) and address 0.

Can someone help me a litle? i found a project with modbus interface, but i can't figure it out how to turn things in my way :)