>> The C64C uses a LH5062 Sharp CMOS part. It might well be faster, but >> who knows. > > There are 2 different 64pin Chips in the C64C, one that includes > the color RAM (252535-01, LR38125 from SHARP) and one that doesn't > (252715-01, LH5062B). Also Sharp; pretty much the same design if you ask me (well, the non- memory part that is); "B" is the speed grade. >> My current theory is all the components are just a little different, >> and it all conspires to make R/#W or #CS too early :-) > > The problem is that the data bus doesn't carry all 1's when idle, > so where do the 1's that video sequencer sees when hitting the > 'grey dots' come from? The internal data bus is precharged during the first halve of each memory cycle. I explained in detail in a previous post. > Another way I have been thinking about is to rig up a +12V > regulator and use a 6569R5 in a board made for the 8565R2 and > supply pin 13 with +12V. Shouldn't be too hard, the voltage doubler > circuit is still there, just needs a 7812 plus some capacitors. If > we still don't see grey dots then, this suggests it's something > with the 856x-VIC. Before doing such major surgery, maybe we should get some more data first: get scope traces of all the relevant signals (clock, VIC #CS, R/#W, #AEC, #RAS, #CAS, some A and D pins) on various different machines. I couldn't find a single bus trace online. >> This hypothesis can be tested, yay! Anyone want to try? Put a scope >> on the analog Vdd, and/or try a bigger bypass capacitor on it. > > I could, but the C64C I have access to at the moment (the others > are stored away) doesn't show the vertical bars. Most C64C only > show them somewhat, they are really visible on a C128 though. None of my C64C do (and no dots either!) Segher Message was sent through the cbm-hackers mailing listReceived on 2011-11-19 23:00:03
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