SCC-I cartridge with 256KB or 512KB

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By Gradius2

Hero (598)

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08-09-2010, 03:21

Everyone should know is very easy to expand the memory from 64 to 128KB and use it just like a MegaRAM, now anyone managed to do the same with 256KB, or even 512KB?

If so, can you please post the diagrams, etc?

I'm not talking about Flash Eprom or CMOS, just using the same DRAM (MB81464) on it.

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By Eugeny_Brychkov

Paragon (1166)

Eugeny_Brychkov's picture

08-09-2010, 07:14

DRAM requires refresh, SCC seem not help in it using its MA lines. Thus such cartridge need to contain SCC access / refresh separation schematic plus additional counter for refresh addresses. That seems too complex comparing to using SRAM as ROM connected to SCC.

By Gradius2

Hero (598)

Gradius2's picture

11-09-2010, 01:58

I see, so it would be a lot easier to use just Flash EPROM on it.

By socram8888

Supporter (7)

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11-09-2010, 17:53

Use a PSRAM (Pseudo Static RAM). It will consume less power and it will be easier to use, since it refreshes itself automatically (PSRAM=DRAM+auto refresh circuit)

By OeiOeiVogeltje

Paragon (1361)

OeiOeiVogeltje's picture

11-09-2010, 18:20

consider the price of a SCC-I cartridge (Snatcher or SD-Snatcher)
then consider the price of a Playsonic

in there there is a SCC-I too with 512 Kb (among other things...)

(proud Playsonic owner)

By RetroTechie

Paragon (1563)

RetroTechie's picture

11-09-2010, 20:59

Use a PSRAM (Pseudo Static RAM). It will consume less power and it will be easier to use, since it refreshes itself automatically (PSRAM=DRAM+auto refresh circuit)
A pseudo-static RAM still needs refresh & be told when to do so, and therefore isn't as easy as an SRAM which holds data as long as power is on. See here for an example where someone thought PSRAM = as easy as SRAM (not... :evil: ). Given today's pricing there's no point in using a PSRAM.

So only choice here is between original memory type (=easy to add to circuit board), SRAM (=simple decode logic) or Flash EPROM (holds data after power off). Or battery-backed SRAM as in-between the last 2.

By socram8888

Supporter (7)

socram8888's picture

11-09-2010, 23:39

AFAIK, Sega Megadrive (Genesis in USA) uses PSRAM (www.segaretro.org/Sega_Mega_Drive/Board_Revisions) as main RAM, but the main processor (68000), and the only that has complete access to the RAM) does not refresh it, and there are no additional circuits to do this

As you can see on TC51832 (main PSRAM of the Genesis) datasheet: http://www.datasheetcatalog.org/datasheets/480/493267_DS.pdf , it explicitely says that it has internal address counter for RAM refresh

You can see a new 64Mbit PSRAM from Toshiba rather than that old from the Genesis, and it still says that it has internal counter to automatically refresh RAM: http://www.datasheetcatalog.org/datasheet/toshiba/1861.pdf

By Bastiaan

Champion (332)

Bastiaan's picture

12-09-2010, 14:46

don't destroy your SCC-I, buy a new megaflash-rom instead
http://www.msxcartridgeshop.com/

or build an ese -scc from an normal SCC
http://www.msxnet.org/gtinter/nogame-e.htm

By sd_snatcher

Prophet (3326)

sd_snatcher's picture

13-09-2010, 01:43

I bought a Mega-flash-rom SCC+ and must say: The cartridge is awesome. It's much cheaper than the original Konami SCC+ and comes with 1MB of Flash. No moding needed.

By Gradius2

Hero (598)

Gradius2's picture

14-09-2010, 05:07

consider the price of a SCC-I cartridge (Snatcher or SD-Snatcher)
then consider the price of a Playsonic

in there there is a SCC-I too with 512 Kb (among other things...)

(proud Playsonic owner)

I have them all, 20xSCC, Snatcher SCC-I, PlaySoniq (still waiting to arrive), anyway, it does SCC/SCC-I by emulation, and I always likes the original sound in this case.

I'm just looking for another little project for fun, not something "ready to play".

I was thinking on Flash EEPROM (if no more simple DRAM was possible), but couldn't find the diagram for 1MB upgrade (just 512KB).

By Eugeny_Brychkov

Paragon (1166)

Eugeny_Brychkov's picture

14-09-2010, 11:07

I was thinking on Flash EEPROM (if no more simple DRAM was possible), but couldn't find the diagram for 1MB upgrade (just 512KB).
You can create diagram yourself (making sure it will be upgradable when larger flash memories will be available!)

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