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How does the cartridge slot get mapped to 0x400000?

Posted: Mon Apr 07, 2014 11:51 am
by Mechanical Menace
Is it something the MD does automatically when the expansion port is used and the cartridge detect pin is low or does the CD bios do it?

Sorry if this is a stupid question.

Posted: Mon Apr 07, 2014 12:17 pm
by notaz
It's controlled by /CART (B32) pin on the cart connector only, if it's connected to ground, cart's /CE (chip enable) signal will respond to 000000-3fffff, else to 400000-7fffff.

Posted: Mon Apr 07, 2014 2:10 pm
by Mechanical Menace
Thanks, that has helped a few things make more sense.

Posted: Tue Mar 03, 2015 1:12 pm
by db-electronics
Now that I think of it, smart address decoding coupled with selective driving of #CART is almost certainly how the Everdrive can loads a CD BIOS from the cartridge port.