Sega/Mega CD BIOS - Help with chip ID

[GordJohnson]

Hi all,

I'm working on my Old Mega CD model 2 console. I just finished removing the BIOS and installing a socket on the board. I will be using an M27C1024 EPROM (UV erasable) chip with region-free BIOS. No issues with any of that.

I have the original BIOS chip sitting here. It is marked as follows:

SEGA
MPR-15511-T
5M62-15-L656
9317EAI JAPAN

It contains NA 2.00 BIOS.

Out of curiosity and boredom, I tried dumping this original ROM chip, so I can run a compare against identical firmware version/region I downloaded elsewhere. I have all the tools to do this (I've used a Phyton ChipProg-48 for nearly 20 years), but haven't been able to find a matching chip profile, since the SEGA chip is masked (in-house part number, obscuring the original manufacturer/part number). I've tried pretty much every profile for *27C1024* and even "27C512*" chips, from AMD, Intel, STM, Atmel, Microchip, Fudan, Saifun, etc. For obvious reasons (ROM vs. EPROM), the M27C1024 profile will not read the SEGA proprietary ROM.

Does anyone know which chip was used for the 40-pin 1-Mbit BIOS in the Sega CD? Obviously, many others have dumped the SEGA BIOS ROMs in the past.

Thank you for any information!

[GordJohnson]

I have since learned Sega used the Toshiba TC531024P-15 for the DIP-40 Mask OTP ROM, and replaced it with their own internal part number. My programmer does not have a profile/support for the TC531024P. The datasheet for this chip is here: https://datasheetspdf.com/datasheet/TC531024P-15.html

Hope this info (even if it's kind of useless) is of interest to someone.

[Xrider]

Hello,

You can read your MaskRom Sega MPR-15511-T with your programmer.
Just disable option "Check ID Chip", and choose M27C1024

On minipro TL866II :

[GordJohnson]

That worked! Thanks...

What's interesting is my supposed North America 2.00 BIOS from the Model 2 seems to have some minor differences when a compare is run against already public North America 2.00 BIOS files. I read my ROM a few times to ensure I did not have any data errors, and it was the same result each time. During the compare, I byte-flipped the image so it was human-readable (same with the other file I was comparing against).

If it matters, this unit was purchased in Canada, in Dec. 1993. Maybe there was a Canadian variation of the North American BIOS, but I doubt it. I have attached the BIOS dump if anyone wants to explore.