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Charles MacDonald
MAME Fan
Reged: 01/06/08
Posts: 25
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Re: DU Update: Final Lap 3
09/30/10 12:15 AM



Phil, you are absolutely correct about the MCU differences. The early hardware used a 68705, and later games (mostly 3D ones with analog controls) used the M37450 which is a 6502 variant with more instructions.

The C68 MCU has a pin to select internal or external ROM that is brought out to a jumper on the motherboard. The pin is latched internally during a reset pulse so subsequent changes are ignored. Just to be sure I verified with a trojan that the pin state really is ignored after a reset.
I also tried various out-of-spec reset pulses, and changing the external memory map in hopes that it might crash. No such luck.

Some games like Suzuka 8 Hours will use the C68's internal ROM and have no external ROM. Others like Final Lap 3use the external ROM exclusively. I feel certain the internal ROM contents are the same for all boards that use the chip.

I sent a C68 to Guru for decapping, it's definitely on the list.







Entire thread
Subject Posted by Posted on
* DU Update: Final Lap 3 SmitdoggAdministrator 09/28/10 08:03 PM
. * Re: DU Update: Final Lap 3 jonwil  09/29/10 01:48 AM
. * Re: DU Update: Final Lap 3 SmitdoggAdministrator  09/29/10 02:00 AM
. * Re: DU Update: Final Lap 3 Phil Bennett  09/29/10 03:00 AM
. * Re: DU Update: Final Lap 3 R. Belmont  09/29/10 10:54 PM
. * Re: DU Update: Final Lap 3 jonwil  09/29/10 03:52 PM
. * Re: DU Update: Final Lap 3 Phil Bennett  09/29/10 09:47 PM
. * Re: DU Update: Final Lap 3 Charles MacDonald  09/30/10 12:15 AM
. * Re: DU Update: Final Lap 3 R. Belmont  09/30/10 09:17 PM
. * Re: DU Update: Final Lap 3 jonwil  10/01/10 01:15 AM
. * Re: DU Update: Final Lap 3 Fever  09/28/10 09:38 PM
. * Re: DU Update: Final Lap 3 SmitdoggAdministrator  09/28/10 09:45 PM

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