Do Step 1.5 games run at 66Mhz?

[Hydreigon233]

I guess some of you may know this already.

I'm pretty sure Step 1.5 games run at 66Mhz. It's been mentioned in the MAME source code that the cpu boards off of a Step 1 and 1.5 are identical. All pcb numbers are the same. There is no mention of "Step 1.5" or "Step 1.0" and no additional on-board components that would change the clock speed (also verified in MAME that running the Model 3 Step 1.5 games at 66Mhz and found no negative regressions aside from the current ones).

Does this mean a "Step 1.5" doesn't exist? The answer is no. It wouldn't be hard to figure the difference comes from the video pcbs since Step 1.5 games had a "faster 3d engine". Both PCB layouts are identical but the 1.5 games use later revision of some Sega custom chips. It's impossible to run Step 1.5 games with the earlier Sega custom revisions found on the older video pcbs The example provided was Scud Race booting with a "JUPITER ASIC HAS THE WRONG ID CODE". I'm going to assume Step 1.0 games can't run on a Step 1.5 video board.

What made me share this was from working on a Lost World pcb stack to notice the video and cpu boards look near identical to that of Step 1.0 (hard to notice the later revision video customs at first). I personally am curious to how initial documentation said Step 1.5 games had the main cpu running at 100Mhz?

[Ian]

The video board is slightly different on step 1.5. The culling nodes have extra data members. There are a few other minor differences as well.

[Bart]

It would be interesting to get a look at the crystal oscillators on the boards, although it's also possible that the multiplier is internal to the CPU. Changing the frequency in Supermodel isn't going to have the same effect as on the real hardware because time delays in e.g. video rendering are not emulated accurately (which is why Supermodel can be "underclocked").

Not sure if I have a photograph of a Step 1.5 CPU board handy. I own two Step 1.0 boards and could compare against those.