I used to design UNIBUS bards in the day. I recall that the 8T26 was a good substitute and there are some pieces of them on ebay.
Marc Howard On Sun, Mar 30, 2025 at 6:55 PM Martin Bishop via cctalk < cctalk@classiccmp.org> wrote: > > https://forum.vcfed.org/index.php?threads/unibus-qbus-alternative-driver-chips.1243045/ > > Found on my travels - should have been attached to my previous eMail > > My summary is "no easy answer" > > Martin > > -----Original Message----- > From: Martin Bishop via cctalk [mailto:cctalk@classiccmp.org] > Sent: 30 March 2025 22:44 > To: General Discussion: On-Topic and Off-Topic Posts < > cctalk@classiccmp.org> > Cc: Martin Bishop <mjd.bis...@emeritus-solutions.com> > Subject: [cctalk] Re: DEC bus transceivers (was: DEC Unibus variants) > > David > > You will have seen my response to shadooo / Andreas. > > Occasional NOS in small quantities excepted, I'm also unaware of slow > transition rate drivers available for purchase. The DS8641 DS3662 DS 3682 > are to my knowledge all unobtanium. > > Your driver design sketches and comments are substantially on the money. > Thank you for making them public. However, an effective implementation in > discrete components would not be "tiny" - even with 0402 passives and a > pick / place machine on the case. Perhaps someday, someone will do a Q/U > driver on a multi project wafer - or is that unafordable. Or, to fly > another kite - what about FPAA (Field Programmable Analog Array) components > ? > > Regarding comparators, as receivers, the TLV3501 (for example) is a 5v / 5 > ns part - add hysteresis and set the H/L thresholds using resistors. > Certainly receives OC signals for me. > > Should you make further progress very interested to hear of it > > Best Regards > > Martin > > -----Original Message----- > From: David Bridgham via cctalk [mailto:cctalk@classiccmp.org] > Sent: 30 March 2025 14:59 > To: Martin Bishop via cctalk <cctalk@classiccmp.org> > Cc: David Bridgham <d...@froghouse.org> > Subject: [cctalk] DEC bus transceivers (was: DEC Unibus variants) > > 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 > >
