Just to clarify, there are essentially three distinct levels of aircraft fit:
Mode S only: the aircraft transmits its hex code, altitude and squawk, but only in response to an interrogation from a ground station
Mode S + 1090ES (Extended Squitter): as above, plus a few additional parameters such as vertical rate and flight ID (callsign), but broadcast continuously without requiring a ground station interrogation
Mode S + 1090ES + ADS-B: as above, but also including navigational data such as position and groundspeed derived from onboard GPS or INS, again broadcast continuously
To complicate matters, aircraft may also have an ELS (Elementary Surveillance) or EHS (Enhanced Surveillance) fit, which allows ground stations to interrogate additional parameters such as airspeed, selected altitude, heading, etc, regardless of whether the aircraft has 1090ES or ADS-B. Unfortunately enthusiast Mode S receivers don't decode this info.
HTH
Dave