Aren't FTDI chips TTL? Such as the one and the arduino Duemilanove?
I would suggest starting here:https://www.google.com/search?q=difference+between+TTL+and+CMOS
or threw it in the trash !
TTL (74LS) is completely obsolete. Even for service replacement (just use a 74HCT part).
AFAIK unconnected TTL inputs are held safely HIGH.
Ah, this is obviously some strange usage of the word 'safe' that I wasn't previously aware of.Douglas Adams, Arthur Dent in "The Hitchhikers Guide to the Galaxy"
As a follow up you might want to look up Don Lancaster's TTL COOKBOOK & CMOS COOKBOOK.Most of these guys either have a tattered old copy or had one at one time and maybe gave it to their sonas a hand me down..
Well they float high, I wouldn't say it was safe because they are prone to EMI pickup in this mode.