FYI - This is how the 115kbaud signal (ie. 0xAA, 0x55 sent) looks like at the 1284p' Rx input when passed via 220kohm serial resistor with 100pF to ground (the "RC filter"). Hard to recommend, though.. The same with 10k pullup on the Rx input. The same with 10kohm serial.. And a picture when connected directly w/o the "RC" filter (FTDI or BT output resistance assumed ~200ohm typically)..
