>> It turns out the (internal) clock drivers and a few other things >> use the >> 12V >> supply on the 6569 (those use the normal supply on the 8565). >> Those can >> sink >> a lot of current I bet ;-) > > Makes me wonder why they did that. Needed +12V for the dotclock and > color clock to work properly? Higher voltage makes faster circuits; for clocks and other big fan-out signals that can be important, so that edges stay steep. I finally figured out one other weird thing: near the RAS and CAS pin drivers there is a huge FET, with quite a bit of logic from all over the place leading to it -- but it doesn't drive anything. On the 6569, you can see where it would have connected: the enable signal for the address pins. And that makes sense for the logic too, it seems it enables this driver when it is actually fetching anything (not a "3fff" cycle). I guess on the 6566 it didn't drive the address bus when it wasn't actually fetching anything; on the 6569 though, the logic for RAS/CAS etc. is already complicated enough, so it was decided to just drive address always > The power comsumption on +12V helps explain why the 6569 runs so hot. 400mW... That's not _that_ much is it? You can do about 2W without heatsink (depends a lot on your package of course). > Without a heatsink you'll burn your fingers on it. Still, it > doesn't seem to mind. TED and the 8501 don't get as hot by a long > shot but are still more prone to die. :( Would be interesting to know how it dies. You can often see it under a microscope, hint hint hint :-) Heat alone isn't such a big deal, but it certainly can be a contributing factor to untimely chip death. There must be something worse as well though. Segher Message was sent through the cbm-hackers mailing listReceived on 2011-09-04 18:00:20
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