this are the requirements in our A/C that may trigger and R/A or a T/A, hope this helps.
Operating transponder for both A/C.
T/A @ 40 sec. from point of closest app.
R/A @ 25 sec. from point of closest app.
R/A req. at least mode C.
Coordinated R/A req. both TCAS equip.
Alt. and Vert. motion are included if A/C is mode S or C equip.
Prox. TFC advisory if within 6 nm. & 1200’ vert.
Vertical motion info is avail if rate > 500’/min.