Re: Ultimax questions

From: Marko Mäkelä <>
Date: Sun, 20 Oct 2013 09:42:02 +0300
Message-ID: <20131020064201.GA4245@x220>
On Sat, Oct 19, 2013 at 06:51:35PM -0400, Steve Gray wrote:
>Will Max support something bigger than 6116? I ordered a few cheap 32k 
>sram chips in sdip that don't take much room... Even if we cant use the 
>whole capacity.

I do not see why not, you should be able to use part of it at least. The 
Max uses static RAMs. I guess you could decipher the maximum RAM map 
from the PLA equations somehow:

Given that the PLA inputs include address lines A12 to A15, I would 
expect the memory to be divided into blocks of 4096 addresses.

Some 15 years ago, I experimented with the Ultimax mode on the C128. You 
can programmatically set the GAME and EXROM lines on the C128 MMU at the 
same time when switching to C64 mode. From that I remember that the 
character generator ROM would disappear from the VIC-II memory map and 
be replaced with floating data lines. I was trying to see what happens 
if both the processor and the video chip is accessing unconnected 
address space for several clock cycles, but did not spend enough effort 
to see how many cycles are possible.

You can always do some bank switching on your own, like I did on the Vic 
Flash Plugin. Are the I/O1 or I/O2 signals available on the Max 
cartridge port? Even the Atari VCS 2600 cartridges can use some bank 
switching, even if the cartridge port does not distinguish reads and 
writes. I wonder how they are doing that, I guess watching for magic 
access patterns, such as read-modify-write instructions, accessing the 
same address three times in a row (1 read and 2 writes).

Best regards,


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