[cctalk] Re: Massbus emulation

What are you emulating - the UNIBUS MASSBUS interface or the MASSBUS devices? If you intend to emulate the interface, have you had a look at the UNIBONE emulator? Using that one reduces the MASSBUS interface emulation to a software problem only. And the community of UNIBONE users would be very happy too if that emulation was added... Jim Bender via cctalk <cctalk(a)classiccmp.org> schrieb am Do., 23. Apr. 2026, 10:46: > Does anybody here still use Massbus? > > Or have a Massbus system you’d like to run, but the idea of dealing with > washing-machine disk drives is a bit less appealing these days? > > In what may classified as a momentary lapse of reason, I have taken up the > old > Living Computer Museum Massbus emulator project and am in the process of > resurrecting / modernizing it. > > Current progress photo here: > > http://www.dmv.net/mbe/mbe1.jpg > > Why, you ask? "Has he gone insane?" are you thinking? > > I have three PDP-11/70s that I would like to get running again. Sure, I > could > cheat and hang a UNIBUS SCSI controller with a ZuluSCSI disk simulator, but > where is the fun in that? Also, the 11/70 was designed and optimized > around > Massbus for primary storage, so it seems only fitting to use it that way. > > The original LCM emulator used a PC with a Mesa 5I22 FPGA card as the > Massbus > interface. The FPGA implemented the drive-side bus logic, while the PC > software emulated the backing disk or tape image. A driver/receiver (“D/R”) > board sat in the middle to translate the Massbus differential signals into > logic levels suitable for the FPGA. It worked... > > Since Mesa 5I22 cards are now pretty much unobtainium, I went looking for a > cleaner and more modern approach. The result is a redesigned D/R board > that > accepts a Terasic DE10-Nano directly. The DE10-Nano is a small Linux SBC > with > a Cyclone V FPGA onboard, so it can host the emulator software itself while > the FPGA handles the Massbus interface duties that were previously done by > the > Xilinx FPGA on the Mesa card. Same general architecture, but much tidier. > > There is still work to do, but it is coming along nicely. The board in the > photo is not yet fully populated, since I am doing incremental testing > before > committing the rest of the parts. > > As I have gone down this rabbit hole, naturally a few questions in the “why > did they do THAT??” category have come up... > paging @Rich Alderson ... > > If anyone here is still actively using Massbus, has experience with the > original LCM project, or just has relevant war stories, comments, > warnings, or > encouragement, I would be glad to hear them. > > Cheers! > Jim > >