[cctalk] Re: DEC bus transceivers (was: DEC Unibus variants)

Does anyone have a list of what boards they were used on? I do have some boards I'm planning or recycling (I know, I shouldn't say that, especially here, but most are common boards nobody uses anymore.) I haven't looked at the IPBs yet, but did plan on pulling some of the chips. On Sun, Mar 30, 2025 at 9:59 AM David Bridgham via cctalk < cctalk(a)classiccmp.org&gt; wrote: > On 3/29/25 7:29 PM, Martin Bishop via cctalk wrote: > > The why not use a UniBone comment has merit, what will your (FPGA) > implementation add ? > > > I'm not shadoooo but I've also been working on a somewhat similar > FPGA-based board called the USIC / QSIC. We started working on it > before the UniBone but have been slower to come to completion. A lot > slower. Maybe there's no point to it anymore but I keep poking along on > the design anyway. > > > > If you solve the (near) unobtanium OC driver / receiver problem - I for > one will be all ears > > > Ah, yeah, this problem. At one point in the QSIC project I started > doodling up circuits to deal with this so we wouldn't have to use up NOS > bus transceivers, wouldn't have to deal with the 5V/3.3V conversion for > the FPGA, and would be all surface-mount parts to make automated > fabrication easier (I never found any DS3662s). A comparator for the > receiver with just the right amount of hysteresis. Have to look around > a little to find one that's fast enough to meet the 35 ns requirement > but they're out there. And then the driver is just a transistor and a > capacitor on the gate/base to limit the slew rate. Shouldn't be all > that hard to design, right? Might want to go with a constant current > source to charge/discharge that capacitor to make it a proper trapezoid > waveform though I don't know that that's really needed. > > This all needs testing and I was going to make up a little test board > with both my circuit and a DS8641 that could be plugged into different > busses to have a look at the waveforms that come out. I looked up the > pinouts for SPC, MUD, and QBUS so I could design a board that would > equally work in all three. > > I was talked out of this idea though. We were doing enough new already > with the whole rest of the board and from our prototype QSIC we knew > that the DS8641s with level converters would work so it made sense to > stick with that. > > Still, I think about this idea from time to time. In the small chance > that anyone is interested, I just now threw my circuit ideas up on > GitHub. Remember, this is doodling. I can see three generations of > ideas in there, as I thought through different possibilities. I also > had this idea about switchable, active termination so that's in there > too, though I'm now less sure that's a good idea. > > https://github.com/dabridgham/DEC-Bus-Transceiver > > Dave > >