Sega Model 2/3 step revision vs conversions

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    • Sega Model 2/3 step revision vs conversions

      Can someone enlighten me as to what's the deal with Model 2/3 step revisions and conversions?

      From what i've read you can only convert a model 2/3 board to another game of the same step (of the donor board) but what is the reason for this limitation? is it something in the roms which dictates this?

      Take model 3 for example, each step just ups the CPU clock speed with the exception of 2.1 which just changes the package type of some custom IC's (according to system16). What stops a higher step board running games from a lower step?

      I can see the logic in a higher step game not running on older, slower hardware but the other way around?
    • Old thread but I just saw this and thought Id' chime in.

      There are other differences beyond clock speed, the ROM mapping is different and there are other bits of hardware too.

      So Model 2 has 4 versions
      Model 2o (original)
      Model 2A CRX
      Model 2B CRX
      Model 2C CRX

      From what I can see from the MAME driver B and C both have texture ram and a co-processor while original and A do not.

      original and A are pretty similar but o has less normal RAM with some extra dual-port ram while A has more normal ram but no dual-port RAM (Maybe some else who knows this hardware better can chime in with any corrections/other differences)

      It might be possible to get 2o games to work on 2A hardware, and to get 2B and 2C games to work on the other hardware but I don't think you'll ever get 2B or 2C games working on 2A hardware.

      Changing which version the game runs on would likely require some patching to deal with the differences.


      Model 3 has 4 versions as well:

      Model 3 Step 1.0
      Model 3 Step 1.5
      Model 3 Step 2.0
      Model 2 Step 2.1

      Step 2.0 and Step 2.1 are functionally identical and games on one can work on the other.

      Looking at MAME source here the clock speed is different from 1.0 to 1.5 to 2.0 and some of the hardware looks mapped differently as well. The ROM boards are laid out different too. Again, it might be possible to port games between steps but would require some patching to do so.
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