Braineack, you're right.
I was going to give you guys a little write-up since I've had a hard time figuring out the problem myself.
First of all let me appologies for my rotten english ;-)
I am going to upload some pictures of all the mod and the megasquirt maybe this evening, since I have to first some good looking once done before. For now I've taken the libary to use some of the pictures coming from the MS2Extra homepage and modefied them.
This applies only for the Megasquirt 2.0 on a V 3.0 PCB running MS2Extra Code.
THE PROBLEM: I was getting no RMP signal while cranking, so obiously MS wasen't even trying to trigger the coils. The output mod as exactly the same as on MS I (see Braineack's write-up).
For the input mod I've refered to the MS2Extra Homepage and the CAS 4/1 mod. (Actually it's the same as the CAS 4/2 mod).
THE CORE: The ms cpu needs to see the same polarity for both signals- CKP & CMP in order to read a valid RPM signal.
It WON'T WORK with just the CKP (primary tach signal). Since the primary tach input (HALL) from the PCB uses the opto isolator (U3) the signal comming in is going to be inverted.
As an conclusion the signal read from the second tach input needs to be inverted too in order to work. The opto isolator that you need to install in the proto area is doing this job for you, while at the same time protecting your CPU input.
Alright, let's first have a look at the input circuit of the PCB (U3 opto isolator)
Notice the way the output of U3 are hooked up.
Let's have a look at the input mod for the cas 4/2 sensor.
Notice the pin (5) on the lower right hand site of the 4n25. That's part of the output to the processor.
Now take a close look at the curcuit for cas 4/1 input mod.
BINGO: There you go, ... you see that one of the output pins from the 4n25 is described wrong (6) you would first need to change that to pin 5. Still there is another error. Noticed the 1k resistor on the signal line going towards the MSII CPU. Go ahead an remove it, since the MSII daughter card has this 1K resistor allready on it.
Those are the two big problems I was dealing with the hole time
You can go ahead and check what you've done by powering up MS (with stim). Using a multimeter messure between ground and JS10. You should be able to get a good 5V reading. Now ground the input line from the secondary tach input (SPR1 from your CAS) you should now get a close to 0V reading.
Do the same on the primary tach input to make sure the input mods are correct. Then set the trigger in megatune to "falling edge".
Like I said, I will do a complete write-up(tutorial) if nessesary. But I guess the little hints I trew should get you back on the track.
Hope that helps a little.
Greetz from Germany,