So, i've checked that if you type \.\COM3 to cmd when a CH340 Uno is plugged in, it resets.
Why does it do that?
Because the serial driver on your PC begins by sending the DTR or DSR, turn on signal and then off. I forget which it is, but it is the driver in your PC that is doing the actual controlling of the serial data.
Hi @the_com3_port. To add to what @Paul_KD7HB said, your UNO board has a special circuit that resets the ATmega328P microcontroller when the DTR control signal is asserted on its serial port by your computer.
If you are curious about this circuit, there is a nice technical explanation of it here:
The reason for this circuit is that the bootloader must be activated in order to upload a new sketch to the board. The bootloader is activated by resetting the ATmega328P. If the board didn't have this circuit, it would be necessary for you to manually reset the board at just the right time during every upload. So the auto reset is very convenient! However, if the reset when the port is opened is problem for you, there are ways to disable it. We can provide instructions for doing that if you need them.
So that's why it resets? Oh. I'l keep it in mind.
Thank you for the respond! Sorry that i couldn't respond any sooner. I was a bit busy.