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Unknown SEGA GG MAPPER CHIP 315-5426
Post Posted: Wed Jan 04, 2017 5:24 am
Hi Folks,

I was poking around the Net looking at some GameGear carts and came across the GG "ROBOCOP VS. TERMINATOR" cartridge. It has a memory mapper chip that I have not seen before.

SEGA part number: 315-5426

I am curious if anyone has seen this pop up anywhere else?
This is the first I have heard or seen this particular Mapper chip.

The Robocop Vs. Terminator ROM is a 512KB image size, so I'm guessing this TQFP version is for 512KB ROMs and not 1MByte like the 315-5912.

It seems to have a similar pinout to the 315-5912 1MB mapper that I mapped out back in 2011 so I was inclined to reach out and see if anyone knows of other games that use this mapper.

See the cart PCBA images below:

CART & PCBA

HI-RES
http://www.digital-circuitry.com/IMAGES/SEGA/GameGear/SEGGA_MAPPER_CHIPS/SEGA_315-5426/x1200/SEGA_315-5426_001.jpg


PCBA 315-5426 MAPPER CHIP

HI-RES
http://www.digital-circuitry.com/IMAGES/SEGA/GameGear/SEGGA_MAPPER_CHIPS/SEGA_315-5426/x1200/SEGA_315-5426_003.jpg

Anyhow,
I'm going to map this one out as well for the MAPPER PINOUT archive, but I would like to know of any other sightings of this little bugger.

So, let me know.
Cheers!
-Gerry
SEGA_315-5426_001.jpg (407.06 KB)
Attachment fairy
SEGA_315-5426_001.jpg
SEGA_315-5426_003.jpg (402.76 KB)
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SEGA_315-5426_003.jpg

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Post Posted: Wed Jan 04, 2017 5:49 am
Interesting, other than a brief mention of it back in 2006 I can't find anything else:

http://www.smspower.org/forums/8052-5100SegaROMsDocumented

Hard to imagine only one game using it though.
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Post Posted: Wed Jan 04, 2017 7:16 pm
I agree with you Charles, it would be hard to imagine that it was developed for a single game.

I wonder if it might have been a custom build, that was requested by the folks over at Virgin for this particular Game they made? and perhaps others that never made it through development.

Perhaps Virgin had plans for something similar to the Codemasters mapper chips?

Interesting indeed.

-Gerry
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Post Posted: Wed Jan 04, 2017 9:36 pm
I think the state of the art in GG PCB inspection is way down, although Bock's dumping logs and checks must help. The discrete mappers are presumably very similar to the integrated mapper designs and thus not too hard to produce, and arguably more flexible because you can add them to any ROM - but it would be weird to find it in only one game.
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Unknown SEGA GG MAPPER CHIP 315-5426
Post Posted: Sun Mar 05, 2017 10:12 pm
So I found another GG cart with this particular 315-5426 Mapper. It is actually a GG Prototype cart for "Bubble Bobble".

Currently listed on eBay by seller "paulweeze71".

eBay item# 322357003878

http://www.ebay.com/itm/Bubble-Bobble-Sega-Game-Gear-PROTOTYPE-Taito-RARE-Undumped-/322357003878?hash=item4b0df98666:g:BwAAAOSwo4pYThAX

I guess there are more of these rare mappers out there.
Pretty Cool.

-Gerry
GG_PROTO_CART_BubbleBobble_04.jpg (168.84 KB)
Bubble Bobble Sega Game Gear PROTOTYPE - Start Screen
GG_PROTO_CART_BubbleBobble_04.jpg
2.jpg (310.34 KB)
Bubble Bobble Sega Game Gear PROTOTYPE - PCB Back
2.jpg
3.jpg (397.38 KB)
Bubble Bobble Sega Game Gear PROTOTYPE - PROM/EEPROM
3.jpg
4.jpg (275.26 KB)
Bubble Bobble Sega Game Gear PROTOTYPE - 315-5426 MAPPER
4.jpg
1.jpg (448.98 KB)
Bubble Bobble Sega Game Gear PROTOTYPE - PCB Front
1.jpg
GG_PROTO_CART_BubbleBobble_01.jpg (244.98 KB)
Bubble Bobble Sega Game Gear PROTOTYPE - CART
GG_PROTO_CART_BubbleBobble_01.jpg

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Post Posted: Mon Mar 06, 2017 3:05 pm
I wonder if the extra hardware on this PCB is used to enable the EPROM to be programmed in-circuit instead of removing it, since removing a non-socketed SOIC package would be very inconvenient.

GG A9 connects directly to EPROM A9. From there, A9 goes into the cathode of the diode, and the anode has a 4.7K pull-up to +5V before going to the mapper chip.

This is important as you need to apply 12V to A9 to read the EPROM ID during programming. This circuit prevents 12V from reaching the mapper chip, and when not programming the EPROM it allows A9 to be connected normally (where driving GG A9 low sinks current through the diode to drive mapper A9 low, and driving GG A9 high does nothing so the pull-up drives mapper A9 high).

I would assume the multiplexers are also used for this purpose, maybe to bypass the mapper's outputs such that the programming address generated by a regular EPROM programmer could be routed directly to the EPROM. I mean they'd need some custom hardware to map the EPROM connector to the GG card edge, but that's simpler than developing an EPROM programmer that knows how to talk to the mapper chip.

Maybe some pins on the GG edge connector were repurposed for this (controlling the multiplexer select input and additional bypassed address line inputs). I also wonder if this mapper is "aware" of a programming configuration and perhaps that's why we see it used so infrequently as it was originally intended for prototypes, and being used on that other commercial game was just done out of necessity.

EDIT: Pin 41 (ground) goes to the select input of at least one (and likely both) multiplexers. It also isn't connected to the other common grounds. So in a real GG this pin is low selecting normal operation, and I guess the programmer could pull it high to pick the alternate configuration. There's three other ground pins anyway, so plenty left.
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Post Posted: Sun Mar 12, 2017 8:08 pm
Hi Charles,
That is really interesting.

I had thought of building a similar type of in-system programmer years back. I guess these PCBA's were potentially only for "In-House" use by developers.

I have to admit, I haven't really seen too many of the 171-5966C PCB's.

It would be interesting to see which version of Board was released in the retail version of this cart.

-Gerry
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Post Posted: Thu May 20, 2021 4:43 am
This mapper also appeared in the regular commercially released version of Sonic 2-in-1 for the Game Gear https://www.smspower.org/forums/11259-Sonic2In1WasUndumpedSonicGameGearGame#1162... which is interesting as both games are in a single ROM and toggled by power-cycling with a short delay
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