tcas
Without going into what the states and other countries require when it comes to tcas how about i give you the basic differences.
TCAS 1 - gives TA's which mean traffic advisories, they make the crew look out and spot the traffic and alert you to traffic you cannot see. (first generation tcas)
TCAS 2 - gives RA's which mean resolution advisories, a voice telling you to climb or decend or monitor your vertical speed NEVER a turn left or right.
Now as far as mode c and mode s transponders.
If both aircraft have mode s transponders, they will talk to each other so to speak and coordinate the RA. For instance one aircraft will be told to climb the other told to decend.
Both aircraft dont need mode s for the RA to work as long as the the other aircraft at least has a mode c transponder (gives altitude) which compared to mode a which does not..
Its simplified but I hope this helps
510