Will depend on aircraft fit:
Aircraft covered under ELS (elementary surveillance) equipage mandate will provide Mode S 24 bit address, altitude to 25ft if available, Mode A code, Flight ID and various status indications.
Aircraft equipped for EHS mandate will provide ELS plus all the IAS, Selected Altitude, Turn rate, ROC/ROD, Mach no, etc.
Where fitted, TCAS RAs and TAs are also broadcast to groundstations.
ADS-B squitter equipped aircraft also broadcast positions, Flight ID and Velocity vector.
Lots of stuff, much more useful than Mode A and Mode C!
RS