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32X question and /TIME usage
cgfm2 - Jun 9, 2006
  cgfm2 Jun 9, 2006
I noticed some of the smaller 32X games such as Space Harrier and Afterburner have a jumper on the PCB that allows the /BYTE input of the mask ROM to be tied low or high; normally high for all 16 bits of the data bus to be used.

Any idea why such a feature would be present? Can the SH-2 in the 32X be set up to run on an 8-bit bus, sort of like some of the 68000 variants that support 16 or 8 bit bus widths? Would the 32X BIOS for the 68K support such behavior or does it make the 68000 execute code out of cartridge ROM during startup?

Also, which cartridges use the /TIME strobe for their on-cart hardware? The ones I'm aware of:

- Super Street Fighter II (ROM banking)

- Phantasy Star IV (ROM banking)

 ExCyber Jun 9, 2006
- Beyond Oasis / The Story of Thor (same banking scheme as PSIV)

 fonzievoltonov Jun 11, 2006
Interesting...

http://www.genny4ever.net/index.php?page=stuff#pic...

See part "The cartridge"


  
	
	

		
		

			Opening the cart, I discovered two jumpers points on the PCB, one soldered.



In the actual jumper configuration, the whole cart is 16bit (like commercial 32X carts).



Editing those jumpers puts the lower part of the cart in 16bit mode and the upper part in 8Bit mode.



I'm 99.9% sure they added those jumpers in the case the board was Z80 based (for cost reasons), but they finaly choosen the 68000 (for speed reason).



This also explain why the 32x startup by itself, because a 8bit cpu cannot startup the 32x?.



So, to conclude, the CPU choice was made at last minute, rushy design.


Could it be the same thing we are speaking here?

Cheers

 ExCyber Jun 11, 2006
Interesting... I know a bunch of copiers (and I think also the Game Genie) took that route for cost reasons, so I guess it's possible.

 cgfm2 Jun 18, 2006

  
	
	

		
		

			Originally posted by fonzievoltonov@Sun, 2006-06-11 @ 06:29 AM



Could it be the same thing we are speaking here?


I think there are a few mistakes with that person's assumption:

- If the system was in Mark III mode and the Z80 was enabled, the cartridge pinout to map Z80 signals to the ROM are incorrect (especially the high-order address lines above A15)

- In 8-bit mode the ROM doesn't function as a hybrid 8/16-bit part, it's strictly 8-bit only with D15-D8 unused.

Given the way the 32X is set up, I think in 8-bit mode it could only conceivably used with the SH-2 set up to use an external 8-bit bus. But the BIOS would have to detect and configure the SH-2 accordingly, and AFAIK it doesn't. Plus the 68000 wouldn't be able to execute code from the cartridge at all.

However, I wonder if this *could* be used for supplemental data cartridges for 32X CD games. Once the 32X booted and was running, it could configure the CS1 space (ROM cartridge) bus for 8-bit mode, and then access the 8-bit ROM directly. Something like the Saturn's ROM/RAM cartridges. The 32X memory map conveniently has an entire CS space devoted to the ROM cartridge, so it can be configured independently of the other 32X memory/peripherals.

Then again for speed reasons you'd want 16-bit mode anyway, but that's the only logical situation where 8-bit mode could be used that I can think of. Unless Sega add the jumper just to confuse people...

BTW, The Game Genie runs normally like other carts, it has two 16K ROMs in parallel to provide data to the 68000. Would have made a cool devcart if it did work in Mark III mode!