[cctalk] Re: Massbus emulation

Indeed. I still have a RM80 MASSBUS drive for MC (Decsystem/20) here, and the thought of firing it up fills me with dread. Running a "modern" SMD drive that plugs into the SMD-ish side of the MASSBUS controller on an RM02/03/05/80 would be the simplest (it's SMD with some signals inverted because DEC is stupid). Running something that attaches to the RH11-C would be ok, but to be honest the Unibone with 18 bit circuitry would be the win. That way it's just a slot on the computer and your disk and tape problems are solved. Chris On 4/23/26 06:40, Hans-Ulrich Hölscher via cctalk wrote: > 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 >> >>