Question about ROM expansion for VIC-20

From: Jim Brain (
Date: 2005-01-15 05:41:50

I am trying to design a 32 kB ROM cart for the VIC-20.  I've found some 
RAM expansions that come close to the design I am looking for, but 
here's the rub:

On a RAM cart, you cna just feed the BLK signals to a encoder and get 
the 2 high address bits.  RAM is contiguous.  No issues.

In a ROM/EPROM, there are lots of options:

8kB ROM mapped into BLK1, or BLK2, or BLK3, or BLK5
16kB ROM mapped into BLK1, BLK2, BLK3
32kB ROM mapped into BLK1
32kB ROM mapped in as two separate 16kB images
32kB ROM mapped in as 4 separate 8kB images
16kB ROM mapped in as 2 separate 8kB images

Does anyone have ideas on how to enable such configurations?  If I 
didn;t have to worry about swapping address lines, I could simply put 
switches on the 4 lines.  ON would enable that 8kB segment.  Since 
address line swapping is needed to implement the above, I thought about 
some jumper blocks.

Anyone have better ideas or know of projects already doing this?


Jim Brain, Brain Innovations                      
Dabbling in WWW, Embedded Systems, Old CBM computers, and Good Times!

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