DIY LTCC or similar system for LT1s

[kur4o]

Here is how PCM interprets opti signal and what it counts.

High res signal is counted at every slot full or empty, totalling 720 counts.
Low res signal is trigger for high res counting. The cylinders are encoded 8 1 2 3 4 5 6 7 in the software.

The rotation could be backwards, not sure. TDC location on the disk is also not confirmed. Someone with dismantled opti could check rotor position and see where the disk is at #1 TDC.

All calculations in PCM are handled by a special third processor. Unfortunatelly I cant access rom section of the processor to make a dissasembly of the code.
If anyone knows how to read the third processor rom or have a dump of it, I will be more than happy to make a dissasembly.

[lionelhutz]

Here is how PCM interprets opti signal and what it counts.

High res signal is counted at every slot full or empty, totalling 720 counts.
Low res signal is trigger for high res counting. The cylinders are encoded 8 1 2 3 4 5 6 7 in the software.

The rotation could be backwards, not sure. TDC location on the disk is also not confirmed. Someone with dismantled opti could check rotor position and see where the disk is at #1 TDC.

All calculations in PCM are handled by a special third processor. Unfortunatelly I cant access rom section of the processor to make a dissasembly of the code.
If anyone knows how to read the third processor rom or have a dump of it, I will be more than happy to make a dissasembly.

Looking at your picture, you can take make a decent guess that TDC will be the leading edge of each low res notch since the leading edges are all equally spaced 45* around the disk and it would only make sense for 1 edge of the low res signal to represent TDC.

It's also possible that the PCM detects the low res notch and then does the detecting to know the next upcoming cylinder so it can then fire that cylinder at the proper BTDC advance. So, the notch everyone assumes represents #1 TDC could really be to tell the PCM it's 45 notches from cylinder #8 being at TDC.