The upper unit fires once per rev as the crank angle sensor runs at half e-shaft speed I think. Lynn can probably confirm or deny. The lower unit tells the computer when to fire the plugs and provides a handy tach signal. We need the green wire to give us a sync signal for our data acq.
BTW this upcoming p-port wave form test is going to give use a million times more data than has been previously available on this subject. I am not exaggerating. Only Mazda may have more info on this subject. In just a few minutes, while the engine revs from 1800 RPM to 6,600 RPM, tons of data will be recorded. 3 data points every 1/1000 of a second. We can see exactly what the p-port runners are doing as far as pressure waves are concerned in a mere instant of time.
Paul Lamar
Hello all,
I need to ask an amateur question...are the crank angle sensors the
same for the 20B and the 13B engines or do they have different
internals (rotating wheels, pickups, etc)?
Thanks much,
John Bell

In theory it could be but I am not sure. I have a complete
stock 20B in the hangar I could pull the top off the
CAS next time I go out there.

Paul Lamar