The Mega Everdrive can act as a RAM Back Up cart for the Sega CD. Will this functionality ever implemented in the standard Everdrive? I already own the Everdrive cart. So it would save me a lot of money if I could use it instead of buying a MegaED.
I don't know if it can. Is the RAM backup implemented on the same address/data lines as normal gave same RAM chips?
Backup RAM for the CD is somewhat different than save RAM... the BRAM cart puts an ID out aliased over than entire first 2MB - the ID tells CD software how big the cart is. The next 1MB holds the actual RAM used... it's normally byte-wide sram with a battery. The last 1MB of space is used for write-protect hardware - writing this space allows you to set/reset the write protection on the BRAM. You can find specific info on BRAM carts over at SpritesMind, but that's the brief overview. The MegaCart, the MD Myth, and the MegaED all support acting as BRAM. I don't know if there's enough gates left in the controller of the ED-MD to support BRAM function.
Ohhhh, so the RAM chip and Flash memory is all going through the FPGA? I thought the FPGA was merely used for the flashing part, never knew it went through it directly first before the console saw the data.
Yeah similar to PSP and Gamecube memory cards, Sega considered the possibility of larger size Sega CD backup RAM carts they didn't release.
Well, you really HAVE to these days... most memory is 3.3V or less now-a-days. You need something that can act as a level shifter, as well as a buffer, and as logic for decoding addresses, and whatnot.
That's what I was afraid of. The EDMD doesn't have strong enough hardware to do the low level converting needed to emulate the RAM cart. Time for me to start saving monies for Mega ED... I'm keeping my EDMD so don't even think about asking for it.
ram cart function, or any other hardware level functions will not be implemented with edmd. edmd CPLD chip already used on 100%
In theory the only thing the EDMD could do is backup the internal BRAM (inside the Sega CD unit) to SD Card. This would not help with getting more total memory to use at once. It would kind of be like the EverDrive 64 idea of being able to backup those Memory Paks to SD card. It would allow you to have multiple sets of saves but not a bigger amount of save data available at once.
That should be doable... activate the CD via Mode 1, and make the sub cpu program look for commands to read/write the internal bram, passing the data in the word ram.
Chilly, I thought you might have written such a program already for the Neo MD. But I sold my Neo MD after getting a Double Pro Fighter and later getting the EverDrive MD. But your work with the Neo MD made it actually reasonable to use.
^ So if this homebrew exists, how hard would it be to port it over to the EDMD. Just curious. I already have a RAM cart so it doesn't matter to me. I'm just asking for others. I know it won't help for the few games that need the RAM cart to function properly but it can help those who have more game saves than the internal memory can handle at once. Sorry if I no make sense. Kinda drunk ATM...
It doesn't exist, but it wouldn't be TOO hard to write. The big issue previously was getting Mode 1 working, but that got worked out last year.
