But this is only on some units. Other units work just fine with the 1k series resistor. The RX on the KL15 goes to 0v.
I didn’t chose the 1k and I don’t think it needs to be there but I would still like to understand what’s going on inside the XMega and KL15 that clamps Vin-low to 2v.
I'm trying to find the UART RX/TX output circuit (the guts in the chip at the pin) of both processors but no luck yet. Could anyone direct me to a schematic of explain it to me?