On Mon, 3 Nov 1997, Daniel A. Seagraves wrote: Remember he has an M9302 terminator. That card will lock up the bus (actually it asserts SACK and keeps it asserted) if the grants are not continuous. On the other hand, having an NPG jumper (the little wire-wrap between pins CA1 and CB1) where you shouldn't have one will cause all sorts of problems. I'm pretty sure that a UDA50 is an NPR (== DMA) device - did you cut the jumper when installing it? Tim : Can you remember which of the 2 UDA50 cards needs to have the NPG jumper cut? Does the other one short CA1 to CB1 anyway? Tracing grants is something you'll get good at if you mess about with PDP11's... -tony

On Tue, 4 Nov 1997, Daniel A. Seagraves wrote: If you can boot RT11, then the grants must be continuous. Is the RX211 nearer the CPU than the UDA50? Normally, if you've left an NPG jumper in where you shouldn't have, then the devices past that point fail to do NPR's correctly. No, I mean on the backplane. The little single-height continuity cards only connect the bus grants. The dual-height ones do the NPG signal as well, _but_ the jumper I mentioned below is still fitted, since a lot of older cards do not short CA1 to CB1 themselves, so the wire-wrapped link is need if you use one of those cards. Absolutely. The wire in question is between pins CA1 and CB1 on the _same_ slot - the slot the control cart of the UDA50 is in. It's a little loop of wire, and is quite difficult to find the first time. When I re-wrap them (say after removing a card), I normally use red wire to make them easier to spot the next time. The jumper shorts NPGin to NPGout on the slot. It must be fitted on slots that do not contain options that use DMA (either empty slots, or slots that contain options that use programmed I/O only - like DL11's, DR11-C's, etc). It must be removed on slots that contain DMA options (like the UDA50). If you just pulled a single-height grant card and fitted the UDA50 card, then I am _sure_ you need to cut this jumper as well. Otherwise NPGin is shorted to NPGout on the UDA50 and the internal grant logic goes crazy on this card (it won't do any damage, though). -tony

On Tue, 4 Nov 1997, Daniel A. Seagraves wrote: You can always solder a jumper back in place. But a 3-in-1 (wrap, unwrap, strip) wirewrapping tool is not that expensive (say about $25, I think), and is almost essential if you work on DEC backplanes (or on a lot of other computer hardware). I'd recomend buying one. For some crazy reason DEC fitted the CA1-CB1 jumper before they put the other wires on those pins. So you have to cut it - you can't unwrap the old jumper, alas. -tony

On Tue, 4 Nov 1997, Tim Shoppa wrote: [NPG jumpers] Hmmm... While such kludges may be great if you need to quickly try a machine with a board removed, I'd rather use a proper soldered or wrapped jumper in a machine I was trying to use. After all, the tool needed to do the job properly is not expensive, and it's useful for a lot of other repairs as well. Why kludge when the proper repair is easier and quicker? I'll remind you of that next time you're sitting alongside a fully stuffed BA11-F trying to remove an NPG jumper from the middle of a DD11-D backplane :-). It's a lot easier to dike it out. And even if you do manage to remove it, you have to put the replacement on top of the other wires - you can't re-wrap it in the same position. I still think this jumper should have been fitted _after_ the other wiring. -tony

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