Forwarding a mail which got lost... ---------- Forwarded message ---------- Date: Wed, 28 Jun 2000 15:47:01 +0100 (BST) From: Richard Atkinson <firstname.lastname@example.org> Subject: Re: Colour RAM Expansion On Tue, 27 Jun 2000, COPLIN, Nicholas. wrote: > 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? According to Christian Bauer's VIC article, it is at the same time as a video matrix access (c-access in the article), which occur in the processor's half of the cycle during a bad line. > 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 This is the correct option but it does not mean that a colour RAM expansion isn't possible. If the color RAM were changed to be 8K x 4 bits and the extra address lines connected to A12 - A10 on the VIC, then an FLI routine would generate accesses to the 8 1K colour matrices on each line of every character row in turn. You'd have to make sure that the 8 video matrices were at 8 locations with different A12 - A10 values, but this happens anyway with consecutive video matrix pointers. Writing to these 8 colour matrices would require extra hardware, since the processor A12 - A10 are always 110 when writing to colour RAM. Richard - This message was sent through the cbm-hackers mailing list. To unsubscribe: echo unsubscribe | mail email@example.com.
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