"Aircraft equipped with TCAS II also require at least one Mode S transponder to provide the data communications needed to coordinate RAs with nearby aircraft."
Where did I get this information? From an NTSB recommendation. I am sure there are other sources on the web. Look at the very bottom line of page 1. It does say TCAS II. I believe you will find that most aircraft with TCAS installed have version II.
http://www.ntsb.gov/recs/letters/1999/A99_55_56.pdf