Hello, I am a beginner with Arduino, I bought an UNO Rev3 board, and had a look at the schematic of this board,
and I have a question about the RX/TX lines usage.
These two lines (of the ATMega328) are connected to the corresponding Atmega16U2 lines in order to upload code
and communicate via the USB cable,
but these lines are also available on a connector for shields (or homebrew extensions), like for example bluetooth.
How can these shields work with the ATmega16U2 TX line NOT DISCONNECTED ?,
is it the 1K resistor that allows it ? (this supposes the TX output resistance of the connected serial device is quite lower than 1k).
In some readings (topics, in this forum), there has been suggested to unplug the USB cable in order to avoid trouble, but it seems for me
that the ATmega16U2 will still be powered (by the then needed external power supply), so this supposes also that this device keeps it's TX
pin in high-impedance (or in input mode) when USB cable unplugged.
Any clarification about (hardware) sharing of the TX/RX lines on UNO Rev3 board is welcome.