A question about using USB serial IOs as one would use Software Serial IO?

Hello all.

I have a general question about the Serial signal via the USB vs the signal via Software Serial.
The two of these obviously differ with the IO pins used.

In the case of the USB serial, say with a 5 volt Nano for example, we have pin D0 as RX.
And in the case of Software Serial - we use a different pin.

But isn't it true - that the incoming signal via USB simply passes through an onboard FT232RL and eventually ends up as a 5 volt signal at pin D0?

In such case, isn't it possible to connect a 5v serial signal directly to DO from a 2nd Arduino?
And it will receive serial signals at D0 just as accurately as it would if those signals passed through the onboard FT232RL?

Or is there a polarity flip in the signal which one would have to take into account?

Thanks in advance!

That is basically correct. Remember the FT232RL output is connected to the arduino and when you connect to that pin you are causing contention and it is a guess which will take control and hopefully nothing burns out. On the good side most boards use a 1K or thereabouts resistor to resolve this conflict. The out going signals will be OK, it is the incoming signals where you will have problems. Also anything you send will also be sent to the serial monitor. Serial software will use different pins and work ok but only in single duplex mode it cannot receive and send concurrently. Pin 13 has a LED connected so avoid this pin if possible.

"Pin 13 has a LED connected so avoid this pin if possible."
Check the Arduino in use - many use a buffer to drive the LED, so there is no resistor/LED connection.

Thanks - I hadn't thought of that!
And that would be the case especially if the FT232RL is holding pin D0 in a fixed state.
Good wisdom!!
Thanks

CrossRoads:
"Pin 13 has a LED connected so avoid this pin if possible."
Check the Arduino in use - many use a buffer to drive the LED, so there is no resistor/LED connection.

Thanks yes - I try to stay clear of using that pin altogether.
Fortunately, most of my projects do not require a lot of IO :-]