On 08/28/2011 06:20 PM, Segher Boessenkool wrote: >>> 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. Too bad... A little blitter in the VIC, wouldn't that have been nice? :) >> 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. Hm, Couldn't make out the driver circuit in the vincinity so I thought it was a input. Too bad they didn't use this signal to generate a 'start of frame' raster IRQ (maskable of course). Yes, you can do this with a normal raster IRQ, but then you have to reprogram the comperator for other raster IRQs. A fixed raster IRQ 'start of frame' might have made some things easier. > The 6569 had none of these pads, FWIW. Maybe they wanted some extra test capabilities to sort out broken chips before packaging them. Gerrit Message was sent through the cbm-hackers mailing listReceived on 2011-08-28 17:00:18
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