>> http://segher.ircgeeks.net/vic-ii/8565R2.xcf (167MB, more complete; >> uploading a new one) > > I'm looking at that one and am wondering about a few pad designations: > > R/_W seems to be an 'input-only' pad since I cannot see any driver > logic next to it. Does that mean that the VIC does not actively > pull R/_W to high when accessing RAM? Yes. It only ever does reads from RAM (or ROM, or whatever), of course. > The circuit diagram for the 250469 board where this VIC was used > shows a 3.3KOhm pullup for R/_W. [Half that actually, two resistors in parallel, if I'm not blind] That doesn't seem to have anything to do with the VIC. Probably bootup conditioning. > Then, below _CS and above LP I see 4 unlabeled pads which seem to > have drivers associated to them but, according to the pinout don't > seem to be used and they have a different form. The lines leading > to them lead towards the video output logic. Testpads? They output the four bits of current pixel colour. Probably test pads yes, they are driven quite weakly. > Same for the pad below LP which suggests an input. It's an output, start of frame (or end of frame) pulse. > Then there is the pad between A5 and A6, it looks as if it was used > but you didn't put a label on it and the VIC pinout doesn't show a > pin between A5 and A6. That's the bias circuit (a charge pump, basically); I think the pad is to add an external capacitor to tune it. The 6569 had none of these pads, FWIW. Segher Message was sent through the cbm-hackers mailing listReceived on 2011-08-28 17:00:03
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