Thursday, February 23, 2017

Fujitsu MB86233 "TGP" DSP

In this post we look at obtaining the Fujitsu MB86233 ROM for the following:
  • #14 Sega 315-5571
  • #15 Sega 315-5572
  • #16 Sega 315-5573

 First decap a sample chip to get more information.  Here's 315-5571:

Which tells us it's contact programmed:

Under 20x brightfield illumination:

Our computer vision expert was concerned automatic capture would be noisy and asked for a 100x die scan.  Unfortunately, 100x takes a long time.  Fortunately, a quick test showed a 20x scan with crossed polarizers has sufficient SNR:

We then fed this into computer vision tools like on 39.  Finally, ROM bit order was swapped around until it disassembled relatively cleanly.  Unfortunately, instruction set documentation is incomplete meaning even correct bit ordering may produce disassembler errors.

Chips around #211 - 218 are suspected to be similar chips and we might take a look at them in the near future.

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To be clear, 14-16 were all decapped and captured (gotta catch'em all!)

#14 Sega 315-5571:

#15 Sega 315-5572:

Similar to above, but takes up slightly more code space.

#16 Sega 315-5573:

This one uses basically all of the code space.  There's also minor overglass delamination in two spots.  Here's the worse one:

Unclear what caused this, but fortunately bits are not obscured by it.  If they were, could probably be removed with brief HF wash.