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Taiwan 8 KB RAM adapter for playing MSX ports on SG-1000 II
Post Posted: Mon Feb 13, 2012 3:14 pm
Attached are pictures of a rare Taiwanese RAM extension adapter to be used to play certain types of cartridges on the SG-1000 II.

Cartridges released by Dahjee or Jumbo among others make use of this adapter to allow porting of MSX1 games to the SG-1000 II.

There's two types of adapter but I was only able to open one of them. I assumed that they were identical but upon late inspection of my cartridge dumps I am finding different use of the memory layout and this assumption that both adapters were the same may be wrong.

Here's the different types of memory usage layout I could find. This covers 5 types of cartridges (5 different cartridge colours/manufacturer) and a total of 15 games.

Type A
Use 8 KB of RAM in region 0x2000-0x3FFF, and 1 KB of RAM in region 0xC000+

Type B
Use 8 KB of RAM in region 0xC000+

Guess: Type A requires Adapter to play on both SG-1000 or Master System consoles.

Guess: Type B requires Adapter to play on SG-1000 and doesn't require adapter to work on Master System.

Question:
Can you tell from the board pictures if the adapter pictured would be able to play both Type A and Type B games ?
In the case of Type A it would redirect range 0x2000->0x3FFF to its RAM chip and leave the range 0xC000+ range accessing the console RAM.
In the case of Type B it would override 0xC000+ range with its own RAM.
Can anybody trace down the connection and logic on the pictures below and confirm that this would be a possibility? Consider the fact that the cartridge are different and maybe through their own signals could direct the adapter.
If this isn't a possibility maybe the adapters are indeed different.

I will see if Wenli in Taiwan can perform some compatibility test with his adapters.
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Post Posted: Mon Feb 13, 2012 4:50 pm
Also, for the "Type B" games, note how with the adapter in place their memory layout correspond to those of a Mark III / Master System. So if the ROM image were named with a .sms extension they would work with most emulators.

However, it is technically more accurate to release them under a .sg extension with a custom mapper (seeing how SG/SMS have other differences than memory and those games were technically released for the SG-1000 II + Adapter). That would break compatibility with most emulators that aren't getting updated.

I am a bit cautious about this move but I think I'll release them as .sg extension to be more correct and hopefully it'll push more emulation author to have a look at all those weird Asian mappers and adapters (for the end user there is always the side solution of renaming files back to .sms extension).
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Post Posted: Mon Feb 13, 2012 6:16 pm
Pretty cool stuff. I think naming it to SG is the proper thing to do.
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Post Posted: Mon Feb 13, 2012 8:07 pm
Another problem that is puzzling me right now is the classification of those games on the website. Example:

- In Taiwan, Tank Battalion is an SG-1000 II game using the aforementioned adaptor and thus using more than the available memory of a regular SG-1000.
(NB: in Taiwan the Mark III/SMS was much less common than SG-1000 II).

- In Korea, Tank Battalion is a Master System game, and much like a lot of port rely on more RAM than what a SG-1000 have.
(NB: in Korean SG-1000 II wasn't released)

Given that, the strictly "correct" way would be to have two /Games pages but it would be rather odd in particular since they are the same game.

(A very slightly odd but less odd case is C_So! which has a regular SG-1000 version but the MSX1 version was ported to SMS in Korea and thus it is classified as SMS. It is somehow more acceptable seeing that the games are slightly different, whereas for Tank Battalion both are ports from the MSX1 version)
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Post Posted: Mon Feb 13, 2012 8:42 pm
Stupid question: is there a difference in the amount of RAM memory between the SG-1000 and SG-1000 II? If so how much do they each have?
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Post Posted: Mon Feb 13, 2012 8:54 pm
Talk about that being a stupid question, I've been actually wondering all day. All legit SG-1000 code seems to clear out 1 KB. Charles' test performed on a SC-3000 refers to 2 KB and I don't recall anyone (me included) actually performing test on an SG-1000 I/II.

I'll give it a try this week, if you're feeling like writing a minimal test program maybe displaying a character for each power of two of RAM i can try it on multiple systems (hoping my new TV would handle the SG-1000).
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Post Posted: Tue Feb 14, 2012 3:19 am
I looked at some PCB photos of various consoles to confirm:

SG-1000 has a Toshiba TMM2009AP
SG-1000 II (single chip version) has a Toshiba TMM2009AP
SG-1000 II (discrete chips version) has a Toshiba TMM2009AP

TMM2009AP is 1Kx8 according to Enri. I can't find a datasheet but I am certain he is correct.

SC-3000 has Fujitsu MB8128
SC-3000H has Fujitsu MB8128

MB8128 is 2Kx8, verified with the datasheet. My SC-3000H notes have the part number written incorrectly (MB82128) which isn't a real part. :)

So the SG* systems have 1K RAM, the SC* systems have 2K RAM. I guess for a computer they realized it would be more useful with more RAM.

About the adapter: I can't quite figure out that adapter from the picture as some connections are hidden under the chips (but not on the back side). If you have a multimeter and can do continuity testing it will make this much easier.
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Post Posted: Tue Feb 14, 2012 6:53 pm
Thanks for the info, should be pretty obvious if most SG-1000 games run with just 1k of RAM. I guess I have to update my emulator now.
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Post Posted: Tue Feb 14, 2012 11:56 pm
FluBBa wrote
Thanks for the info, should be pretty obvious if most SG-1000 games run with just 1k of RAM. I guess I have to update my emulator now.

For information, MEKA has been running with incorrect settings for SG-1000 as well since ~10 years :). I don't think any official game rely on memory mirroring because else they wouldn't function on the Master System, but there might be some odd case/bug where this could happen.
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Post Posted: Thu Jun 26, 2014 4:27 am
Ohh...I have never seen it before.
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DahJee on Sega Mark III/Sega Master System
Post Posted: Sun Feb 14, 2021 5:33 am
So if I were to play a DahJee MSX to SG-1000 conversion on a Master System/Sega Mark III (Specifically on real hardware) by converting the sg1000 rom to a master system rom using the "sg2sms" software, would it still require the DahJee RAM extension adapter?
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