Colour RAM Expansion

From: COPLIN, Nicholas. (
Date: 2000-06-27 04:31:33

Hi all,
I recently had time to think about a colour RAM expansion for the C64 and
what prospects it could offer, but I'm not sure if I got the logic correct,
and also have very little info about the way the VIC grabs the colour RAM

I see from the circuit that the VIC has dedicated lines from the colour RAM
so setting up a palette table would be easy (ie use the 4-bit data to index
a RAM/EPROM table and feed this into the VIC), but the only functions I
could see would be to convert colour to grey or inverse....

My thinking was to create a mode where an 8k colour RAM buffer was possible,
hence a 4bit colour byte was available for each byte in the hires map (of
course only in MC hires would the colour RAM be of use).  Doing this would
increase the colour independence (without CPU intensive routines), but
whether this would work or not depends on how and when the VIC actually
grabs the colour nibble?  Does any body know?

Option 1a) would be if colour info was grabbed in parallel to reading the
Video RAM and then stored within the VIC for the next 8 reads of the Hires
RAM. This would mean an expansion is not possible
Option 1b) would be if colour info was read in parallel with the video RAM,
but one for each hires RAM byte... which would mean a counter is required
Option 2) would be if colour RAM is always just the lowest 10 address lines,
and hence if the next three address lines were connected, 8K colour RAM
would be available ono-for-one with the HIRES reading (still have to devise
a way to actually set the values, but the VIC would read it no problems)

Anyone have any ideas?

- Nick

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