To study the ATMEGA MCU, I am installing an ATMEGA168 on a breadboard. Power is supplied by a 9V battery whose voltage is stabilized at 5V by the classic 7805.
Now to make debugging easier, I thought of using the USART to display the values of the variables through a serial connection through PUTTY. On my computer, I install an FT232 USB-SERIAL converter with FDTI chips. I know that if I set the FT232 to work at 5V the micro RX pin in addition to receiving data also starts to power the microcontroller.
Why this? I tried to understand from the datasheet dell'ATMEGA, but I can not give me an answer.
However, I have found that if I do so the FT232 works at 3.3V, then the microcontroller will not power, if not when it is powered by the 9V battery.
In the breadboard, I put a button to reset the micro, and in the code, at the start, a greeting is sent. So when I keep the FT232 connected and turn off the power from the 9V battery and press the reset button in the serial monitor, I see the greeting message, indicating that the microcontroller is powered by the RX pin.
I would be grateful if you can explain the reason for this behavior. I also tried to look in the Electrical Characteristics section, but I could not figure out why.
Consequently, components that communicate via serial with ATMEGA must have a working voltage of less than 5V?
If you need I could provide you a image of the circuit.
Thank you so much, and I apologize for any trivial question.