Hi,
yesterday I´ve found an interesting thing, which I didn´t know until now. On pin "S" of the cartridge-slots of an Atari 800 there´s not the "PHI2" signal attached as on all newer machines - there´s "RAS" connected. The falling edge of PHI2 and RAS is nearly the same, but RAS is much shorter low than PHI2 (of course, there must be some time for CAS, too).
Most modern circuits (in flash-carts or flashable carts) sample the PHI2 signal for their logic. So I think, this might be most sig