256K C64

[jamesk]

So my IIgs upgrade left me with eight 41256 DRAM chips. I was thinking.. what could I do with these things. Then it dawned on me. What if the DRAM in the C64 was pin compatible with the 41256 DRAM. Maybe I would just have to add an extra address line like I did with the IIgs. Well it turns out, it's been done before:

 

http://www.ktverkko.fi/~msmakela/8bit/memory/index.en.html

 

The old DRAM is replaced with 256 chips. An extra address line is added. A 6821 controls the logic. So the downside is, I don't have a 6821 sitting around.

 

http://www.facebook.com/album.php?aid=2092497&id=1458531880&l=3d34937604

 

Here is a schematic where the 6821 is replaced by seven HCT chips to handle the logic. This was designed for the plus 4, but I don't see any reason why it wouldn't work with the C64. The page says it's compatible. I don't as of yet understand the logic used.

 

edit:

 

The 6821 is $4 at Jameco.. maybe that route is the KISS route.

Edited February 10, 2011 by jamesk

[Hatta]

Very cool. Looks like cbmlink would be a real nice alternative to an x1541 cable for those without flash devices.