Hi Simon,

there are 2 sorts of noise:

1.
If noise are voltages always below the signal amplitude, a Schmitt-Trigger works well.

2.
If noise on an equal amplitude, but always shorter you need digital filtering.
On using the build in UART there is always such filter hardware implemented:
The receive signal was sampled 3 times in the middle of a bit time and the most sampled level was accepted (majority logic).


Peter