Re: Hiding code from the User...

From: Nicolas Welte (
Date: 2001-04-02 13:30:36 wrote:
> But how to do some of the other devices work:
> RAMLINK (in particular where does RLDOS live)??

I'm sure it is mostly a kernal replacement that lives at $e000 and uses
Ultimax mode to map into the C64. This is why it needs the extra cable
attached to the HIRAM signal in the C64 to allow access to RAM at $e000. I
have no idea where it maps the rest of its ROM when needed, but it can be
everywhere from $1000-$ffff. I can't check it, because all I have is a
broken, non-working RAMLINK board. Some GALs seem to be dead :-(

> Epyx FastLoad (there's only a ROM and logic here)??

There once was a thread in comp.sys.cbm about this cartridge, called "epyx
fastload internals" or something like that. I think parts of the ROM are
mapped into I/O space, and accesses to I/O space trigger a circuit that maps
in ROML for a certain time. After a timeout the ROM vanishes again. Quite
tricky :-)

> Action Replay (EPROMS, RAM and Logic)??

The AR is very well understood, there are even docs on funet to make your own
clone. Another very good source for cartridge information is the source code
of the VICE emulator. 

> How do the C128 carts do it?

Nothing special, I guess. Without any extra circuit the 128 can address 32k
ROM on an expansion port card (minus some bytes for MMU addresses).

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