8Mo cartridge with SRAM, HELP

[oofwill]

Hello

I designed a 8Mo cart with SEGA mapper, using the logic sheme of Megavolt.



I am trying to build a cart with FRAM, but i can't achieve to make it working.

I already made a pcd for 4Mo games and i made SRAM works using a 74HC74 and 74HC139 couple to select the rom or the ram chip (using TIME and D0 signals)

Obviously, this does not work with the SEGA mapper and i can't figure why.
The cart works perfectly for standard game (Tested with SSFII) but if i try to use with the SRAM hack, it seems that the mapper does not work anymore because the screen is glitched.
Is there anybody to help?

i'll try to post capture of my schematics

[Chilly Willy]

You should be using Y0 of U8 to control the save space mapping. ROM space and SAVE space share the same map - ROM at 0x000000 - 0x3FFFFF, and SAVE at 0x200000 - 0x3FFFFF. Most of the time, you'll not be using all of save space... most flash carts only provide 32KB of save. Some more, some less. But F1 controls the save space - b1 = WR_PRO = 1 = save ram write protected, set to 0 to write. b0 = SS_ENA = 1 = enable save space at 0x200000, set to 0 to enable rom space. You'll see a line like this in the startup of games that support the Sega standard for save ram:

Code: Select all

        move.b  #2,0xA130F1         /* SRAM disabled, write protected */

The cart should come out of reset/poweron with the rom space enabled.