Pushing the Classic II over the 10mb limit?

[uniserver]

Looks like there is 2 different kinds of Classic II main boards.

Looks like the main difference seems to be the ROM I/C's.

The Earlier Classic II Version had 4 ROM I/C's

The Later Classic II Mainboard had only 2 ROM I/C's

I was going to maybe start by experimenting, and changing the later CLASSIC II's Roms with maybe ones from a LC-III.

see what that does?

Maybe slap a couple of 16mb simms in there?

Anyone have any ideas? If that doesn't help, I would like to find the what is limiting the ram...

 

[Paralel]

The Classic II isn't the only one that suffers from this issue, no? I figure it must be something all the models share in common.

 

[CC_333]

My understanding is that it's based on the LC I architecture, which is affected by this limit (and so to are various other machines which are based on it, of course).

If the limit can be lifted, great! But I'm not totally sure it's as simple as changing ROMs with a later system (though that might enhance other aspects of the machine, I suppose). Somehow, I think It could be some sort of limit that's built into the hardware.

We might have to consider not only changing the ROMs, but perhaos also replacing the MMU (if it's a separate chip) or whatever it is, and rework the board so that it'll work (if that's even possible).

...goes back to do more homework...

c

 

[Trash80toHP_Mini]

IIRC, I've read here recently that it's the way the ASICs of the LC are set up that screws with the memory, not the ROMs.

 

[gobabushka]

That was always my understanding as well. Would the ASICs just impose some sort of address bus limit? What about some sort of extension that could jump beyond that address limit. If this is a ROM limitation couldnt someone code a patch driver, that could execute a jump instruction to an address outside the limitation, or am I wayyy off here?

 

[trag]

First thing to check is whether the twelfth address bit is wired up in the SIMM sockets. Without that, the machine cannot physically address a SIMM larger than 4 MB. It's pin 24 in the socket.