I have an application where multiple Arduinos communicate with a central Arduino via serial. It seems that the central TX pine can be connected to multiple remote RX pins (I haven't figured out what the max fan-out is).
However, the opposite doesn't seem to work, eg, multiple remote TX pins tied to the single central RX pin.
This tells me the RX pin is a passive pull-up, while the TX pin is an active high. Is this right?
Do I need to buffer all the remote TX through a multiple input AND gate?
I was under the impression that the TX pin was an open collector output with a passive pullup, so that it was only active low.