Has anyone figured out the details about how to use DRAM on the Genesis? I'm assuming it is capable of automatic refresh, which would simplify the glue logic used. My guess is that the DRAM control register at $A11000 is used to enable it, periodically halting the 68000 to insert a refresh cycle.
But I don't know the details; for example the cartridge port has two /CAS strobes and no /RAS. Likewise the expansion slot has two /CAS, one /RAS, but no /AS so I don't see how external logic can know the address bus is valid.
Also I'm wondering what limitations there are on how many addresses are refreshed, basically what the size of the refresh counter is. I'd like to think it could handle 4MB, but it could be much smaller.
Any tips?
But I don't know the details; for example the cartridge port has two /CAS strobes and no /RAS. Likewise the expansion slot has two /CAS, one /RAS, but no /AS so I don't see how external logic can know the address bus is valid.
Also I'm wondering what limitations there are on how many addresses are refreshed, basically what the size of the refresh counter is. I'd like to think it could handle 4MB, but it could be much smaller.
Any tips?