Nice bits of info 😀 Sent from my iPhone
> On Mar 29, 2025, at 13:06, Milo Velimirović via cctalk > <cctalk@classiccmp.org> wrote: > > > >> On Mar 29, 2025, at 12:33 PM, shadoooo via cctalk <cctalk@classiccmp.org> >> wrote: >> >> Hello, >> I'm searching information about all existing variants of DEC Unibus in >> Dual/Quad/Hex flavors. >> I read the "UnibusSpec1979.pdf" on bitsavers, which reports a "Standard >> Unibus" pinout in the last pages. >> However in several backplanes "Small Peripheral Controller", "Modified >> Unibus Device" and "Extended Unibus" are supported. >> Maybe also other unlisted Unibus variants do exist (e.g VAX 11/730)? >> I also found the gunkies.org WIKI very helpful, however it is still quite >> difficult to compare the pinout differences (dummy proof). > > Try this one: > https://hampage.hu/dr/unibus.html > >> >> Where could I find a specific DEC documentation about the more recent >> variants, similar to the 1979 specs, but referred to SPC, MUD, EUB, ect? >> >> Big doubts: >> - why DEC, having defined the dual Standard pinout, had then to implement >> the quad SPC backplanes? > > The “dual Standard pinout” for slots A/B was generally used for a BC11-A > Unibus cable, > with a Unibus terminator in the very last slot. The Unibus cable carried > signals (not power!) between backplanes. > > Quad SPC is common to (at least) Modified Unibus(MUD) and Standard Unibus. > The differences > between the two backplane specs are in slots A/B only, with slots C-F the > same (AFAIK.) > Also some slots of the of the VAX730 backplane. > >> - why DEC, having defined quad backplanes, had then to implement the hex >> (standard + SPC) or (MUD + SPC) or EUB? > > Probably due to changes in cabinets and packaging. The 11/20 was unique in > having a quad > backplane mounted from side to side in a BA-11 (and upside-down too!) Most of > the subsequent > Unibus pdp11s had hex backplanes mounted either vertically, top to bottom, > (11/40, 11/45 and > 11/70,) horizonatlly, front to back, (some 11/05s, 11/34, 11/35, 11/44 etc.), > another > orientation was vertically to one side, front to back in 5.25” cabinets. EUB > was unique to > the 11/24 and 11/44 and only for memory boards. > [https://gunkies.org/wiki/Extended_UNIBUS] >> >> >> I mean: given that in AB all Unibus signals are present (from >> specifications), what is the need for CDEF? > > The ability to use larger printed circuit boards; it gets you higher density > and avoids the need to run (as many) interconnects off the board and thru the > backplane. Remember that 50-60 years ago was the era of 14,16-pin DIP > packages for small-scale and medium-scale > integration; larger packages existed of course, but they were the exception. > You still > needed lots of wires to interconnect functionality between chip packages. > Using a hex > board instead of single or dual boards allowed many of those “wires” to be > traces on a PCB, rather than run through the backplane or on an over-the-top > jumper. (See the 11/34a.) > >> Provided that several signals are duplicated in hex pinout, the backplane >> will connect homologue signals together, >> or AB bus will always be separated from CDEF bus? >> >> My aim is to design a reprogrammable digital logic board which could be >> employed in any system, >> using 18bits address or also 22bits (i.e. for 11/24). > > See the Unibone, to ensure you’re not reinventing the wheel. It also includes > a Unibus description that might be helpful. For something simpler take a look > at the M1710 Unibus Interface Foundation Module. Brochure: > https://vt100.net/manx/details/1,22302 > > https://retrocmp.com/projects/unibone > > —Milo
