Gameboy Development Forum

Discussion about software development for the old-school Gameboys, ranging from the "Gray brick" to Gameboy Color
(Launched in 2008)

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#1 2008-07-16 12:15:02

From: Asturias, Spain
Registered: 2008-07-09
Posts: 10

External interface on cartridge

I'm working in a Flash Cart as you can see in this thread: … .php?id=38
Now i'm thinking on adding features to it, like 128K Save RAM (planned) and an interface to access external hardware.

So i'm thinking on a way to use the cart bus to write/read data to/from something different than the ROM and SRAM.
As my cart uses MBC5, If address A000 (normally used to access cart RAM) is used, the ROM is disabled (as ROM /CS is connected to A15), but to enable the cart's RAM, you have first to write 0Ah to 0000-1FFF.

So, if I write/read from A000 without enabling cart's RAM, I think I can access some external interface, do you think I'm right?
I'm thinking on NANDing A15 and Cart's RAM /CS to obtain a /CS signal to this interface. (if sram and rom are disabled, external stuff is enabled).

What do you think about this?




#2 2008-10-12 02:08:43

New member
Registered: 2008-10-12
Posts: 3

Re: External interface on cartridge

I'll have to look at what info I have on the MBC5 again, but there might be a pin or combination of pins that could be something like a /CE for RAM? You could then disable RAM (don't know if this trashes what's in it!) to allow writes to A000-BFFF where you have external I/O, then re-enable RAM when you're done. You might also want to check out using one of the upper address lines on the MBC5 to enable/disable stuff like the rumble carts do. Lots of info over at:

Hope that helps...

Update: Here's the site I was looking for - lots of good info on interfacing with the cart: … ;GBcontent

Last edited by CrazyJoe (2008-10-12 02:12:27)



#3 2008-10-16 01:04:50
Registered: 2008-04-04
Posts: 20

Re: External interface on cartridge

Take a look at :
I haven't external RAM. I/O are very powerfull and can interface a lot of things (including serial RAM)



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