TX diode don't get fired with unplugged USB

Projects General Guidance
1

Hi All.

I compiled standard sketch. It prints a message to the serial port.
If I power arduino with USB TX diode fires when message is transmitted.

TX doesn't work if arduino is powered through pins (5v and gnd).

Diode of 13 port blinks regularly (it's my check) in any case.

I tried to connect 2 arduinos tx -> rx and rx -> tx
but diodes still not fires.

2

The TX diode is controlled from your computer not from the arduino. So it will not light up if it is not connected to a computer.

3

The TX & RX LEDs are controlled by the USB to serial chip
not by circuitry that monitors the TX and RX lines connected to the AVR chip.