Stby is right answer
Until you operate into an airport utilizing multilateration technology, which requires the transponder to be set to ON/ALT (TA/RA in some machines) during taxi operations.
TCAS II is normally inhibited below 800' or 1200' (model dependent) to avoid conflicting warnings with a GPWS/EGPWS and the stall warning system. For want of a more technical description, it is degrading itself to act like a TCAS I.
jtr, I feel your "definitive source" would be the Jepp manuals (or whatever chart system you use) that will describe what to do with the transponder at the airport(s) you operate from.