96Mbit SNES Cart



Kyuusaku's Decoder


The Address Bus Connections





   X = No Connection
   Connections are horizontal

SNES 32Mb ROM 64Mb ROM 8Mb SRAM
A23 A21 A22 A19
A22 X X X
A21 A20 A21 A18
A20 A19 A20 A17
A19 A18 A19 A16
A18 A17 A18 A15
A17 A16 A17 A14
A16 A15 A16 A13
A15 X A15 X
A14 A14 A14 X
A13 A13 A13 X
A12 A12 A12 A12
A11 A11 A11 A11
A10 A10 A10 A10
A9 A9 A9 A9
A8 A8 A8 A8
A7 A7 A7 A7
A6 A6 A6 A6
A5 A5 A5 A5
A4 A4 A4 A4
A3 A3 A3 A3
A2 A2 A2 A2
A1 A1 A1 A1
A0 A0 A0 A0


The 32Mbit ROM must map to 00-3f:8000-ffff and 80-bf:8000-ffff banks 00-3f will map the first $200000 bytes of the ROM. When the ROM address reaches $200000, A21 gets set, since this must be connected to SNES 80:x000, Rom A21 must be connected to SNES A23.

For the 64Mb ROM, it must map to $40-7d:0000-ffff, and c0-ff:0000-ffff. One 64KB chunk will be lost to banks 7e-7f system RAM. That would be the 32nd Mbit of this 64M chip. This means A0-A15 of both SNES and ROM connect.

For the SRAM, you can map up to $10:0000 bytes from $00-3f:6000-7fff, and 80-bf:6000-7fff. You can wire in less, simply use less, same goes for the ROM chips. Mirrors are produced automatically. Here is an 8Mbit SRAM: http://uk.farnell.com/alliance-memory/as6c8008-55zin/sram-8mb-2-7-5-5v-1024kx8-tsop44/dp/1562904

Note: Star Ocean cart has 64Kb SRAM ($2000 bytes). Unknown whether larger SRAM can be used (64Kb mirrors used??)