Rounding off edges of a square wave ?

I'm working with a square wave format that is close to the SAE 1850 spec and I read in a whitepaper that all the waves have "rounded off edges"

They say they do it for noise... ?

If I'm using a pic to put data on this bus, how do I round off wave edges, or do I even need to ????

Thanks!

The sharper the edges on a square wave the more hagh frequency harmonics it has. So to reduce noise you can round of the square wave as long as it still meets the risetime requirements. A simple RC filter would do it.