Originally Posted by Joe Perez

In '95.5 - '97, the crank sensor was used only for misfire detection, while the CAS was used for the staging and timing of both the fuel injectors and the ignition coils. The CAS in all NA cars outputs two signals, which are conceptually comparable to combined crank and cam sensors in the NBs. One signal is four evenly-spaced pulses per cam revolution (one pulse per ignition / injection event) and the other has two uneven pulses, from which absolute engine position is determined.) Thus, an NA can derive both the timing of the engine as well as the phse of the engine from just that one sensor, with the disadvantage of having some jitter introduced by the cam belt.

From '99 onwards, the crank sensor became the timing reference for fuel injection and ignition, while the cam sensor provided the staging reference (eg: so the ECU can tell which crank pulse corresponds to which cylinder.)

On the VVT cars, the cam sensor additionally allowed the ECU to judge the exact angular position of the intake cam, by comparing the phase angle of the cam sensor to the crank sensor.