using DDR , SDRAM externally ?

[camp david]

only I need to make a genesis sega cart (U MK3)
because it's unavailable in our markets

any way I would like to thank you all
for great information .

[ckielstra]

We are thinking way too difficult for what he wants to build. The Sega Genesis is a very old game console where you insert a ROM module. The ROM module is directly connected to the Sega memoy bus.

You can create these modules with just a simple Flash memory chip. Only problem is that the modern Flash chips run at 3V so you'll need a voltage conversion to 5V. Cheap chips exist to do this.
Or you try to get hold of the older Flash chips running at 5V and accept that these have smaller memories.

With the large memories you can use your PIC processor to select from one of the many games stored in ROM.

With a simple Google search I found a 'programmable' Sega Genesis module that's not even using a microprocessor at all: http://raphnet.net/electronique/genesis_cart/genesis_cart_en.php

[camp david]

this cartridge 8 mbits = 1 mbytes : 2 ICs
so I need 8 ICs for MK3 rom which it's size is 4 mbyte
.
is this reasonable ?

[ckielstra]

Yes, you could do it with 8 chips of 4Mbit.
Or with one 32Mbit chip (2M x 16).

The technology is simple. What makes it difficult is that the technology is old. The article I linked to is from 2005 and the Sega Genesis game console is from 1988.
5V Flash chips are not common anymore, everything is 3V now.
When I had a quick look at the website of one of the larger electronics shops, everything larger than 8Mbit has to be ordered.
You could do it with 4 x 8Mbit chips, about $3 each = total $13
Cheaper is to use the ancient EEPROMS. You can buy used 27C322 32MBit EEPROMS for about $4 on ebay.

This thread is going off-topic and has nothing to do any more with PIC programming. I suggest you try searching the internet. Search for Genesis and 27c322 and you will find many ready made projects.

[camp david]

the price is not an issue
our markets is no more contains these stuffs
and buying online isn't available for me
if I could buy online , then I would buy a "sega genesis everdrive"
it's an SD CARD based cartridge

can you give me a number of a modern flash with 32mbits ?
perhaps it's found in some devices I have & I dont notice !

[ckielstra]

The market you live in sounds hard.
Your project is not very difficult and given all new electronic circuits that have been developed since your Sega came to the market, there are multiple solutions. I've given you a few suggestions which you say are impossible for you because of missing parts. I don't know what parts you do have access to, so this isn't going to work.
You'll have to get creative.

[Ttelmah]

I already gave part numbers for a number of 4M*16 memories.