Ocean 256K cartridges / 256K EPROMs?

[modeler]

Hi Marko,

Re. https://github.com/msolajic/c64-uni-cart#ocean-256k specifically the part that says:

"Use a 512k EPROM or FLASH. You need to program the same image in both 256k halves of the EPROM"

This does work fine of course, but I was curious to see if a 256K EPROM would work in that configuration so I tried Shadow of the Beast with a W27C020 flash PROM and an AT27C020 OTP PROM. Both worked fine with MODE Ocean, LOCK No, SIZE 16k, GAME connected, MD disconnected, resistor and diodes installed (as documented).

I tried some other 256K Ocean carts i.e. Robocop 2, Battle Command, Chase H.Q. 2 and Space Gun (I think that's all of them!) and the all worked. Were there known issues with 256K EPROMs hence the advice to use 512K with concatenated binaries? Just interested to know.

I've also had no issues doubling up 128K binaries and using 256K EPROMs.

Thanks,
Dan

[msolajic]

Dan,
I have wrote it this way, since VICE manual (which may not be perfect) says:

The 256Kb type of cart has 32 banks of 8Kb ($2000), 16 banked in at $8000-$9FFF, and 16 banked in at $A000-$BFFF.

I have actually never disassembled the code or had a physical Ocean cart in my hands at the moment of writing that to confirm or deny the above statement, so I wrote to use a 512k flash. That way, if the cartridge is in 16k mode, the highest address line is controlled by C64 A13 and the code can be seen in the $A000-$BFFF range if needeed (it now resides in the last quarter of the 512K chip).

Hope this helps,
Marko