See Figures 1 and 2
The CA16DE and CA18DE engines use a Direct Ignition System (DIS). This system has no conventional distributor or high tension wires. Instead, small efficient ignition coils are fitted directly to each spark plug.
The DIS system uses a crank angle sensor, as does the later model conventional distributor. The sensor monitors engine speed and piston position. It sends signals to the ECU for control of fuel injection, ignition timing and other functions. The crank angle sensor has a rotor plate and a wave forming circuit. The rotor plate has 360 slits for one degree and 4 slits for 180 degrees. A Light Emitting Diode (LED) and photo diode are built into the wave forming circuit.
When the rotor plate passes the space between the LED and photo diode, the slits of the rotor plate continually cut the light which is sent to the photo diode. This causes rough shaped pulses. They are converted into on-off pulses by the wave forming circuit and are then sent to the ECU.