IIRC I wrote that as I compared the C128 VDC register description with the CRTC register settings. The first 20 registers look very similar if not identical (except for mode register R8).
Of course they are not compatible. CRTC has no color handling for example. But the memory address generation of the VDC is very similar to the Rockwell 6545 in its "Transparent Adressing" Mode, where the CPU writes the address it wants to access in the video memory to the CRTC and the CRTC then controls the video RAM address lines for the CPU data transfer. The mode is explained in
http://www.6502.org/users/andre/hwinfo/crtc/diffs.html
As you say, Commodore might well have taken most of the CRTC logic blocks and added the color handling to it to create the VDC.
André
kc5tja wrote:
fachat wrote:
The 8563 seems to be a direct descendant of the 6545/6845 CRTC. You can find some info on those here:
I remember reading register descriptions for the 8563 years ago; I don't believe they're compatible chips. I think, by "descendent," Commodore might have meant, "We took the major logic cells from the 6545 and re-used them in the 8563." I don't think that they're register compatible at all, however.
This is, of course, assuming my memory is correct.