Internal memory at I/O 2 and 3

[doug_in_nc]

I just had my favorite sort of idea - a bad one. Has anyone tried to expand the VIC by putting in 2K of RAM at I/O2 and 3 internally, ie that can be seen by the VIC chip? Unless I have made a mistake, that looks like it would be a good place to relocate video RAM. If it were possible, that would free up the whole RAM area from the top of zero page to the end of block 3 for BASIC if it was fully populated, while still giving 2K of video memory to push the limits of the VIC’s graphics capabilities. I know some people here have installed a 3K block at RAM1-3 which allowed video memory expansion and/or a larger block for BASIC, but I haven’t been able to find anyone who has done so with I/O 2&3, which admittedly rather suggests my idea won’t work.

[Mike]

viewtopic.php?t=7750 ...

In short: yes, putting internal RAM at I/O 2 and 3 - so that the VIC chip can 'see' it - is possible. Doing so is however slightly more complicated than adding internal RAM at $0400..$0FFF.

[doug_in_nc]

Thanks. I searched for a while last night, but I didn’t find that thread. I guess I’m going to have to sit down with a schematic and try to work out exactly what was discussed both in that thread and the earlier one that referenced your design for the internal 3K (which I had found and read). If nothing else it should be a good exercise and a way to understand better how the VIC works.