[cctalk] Why do we do these things? (was: Massbus emulation)

Why do we do these things? I'm working on porting a multitasking forth I wrote in the 80's to a Mac plus rom replacement. Jim. On Thu, Apr 23, 2026 at 12:10?PM Chris Zach via cctalk < cctalk(a)classiccmp.org&gt; wrote: > Jim: > > Oh absolutely, and no shade meant on the problem. The Vax 8600/780/750, > the pdp11/70, and the DecSystem 2050/2060/2065all have dedicated Massbus > channels that don't deal with Unibus. So a device that plugs into the > end of a MBA cable would be neat without a doubt. > > My 2020 is one little chunk of the puzzle, and I am planning to get a > pair of Unibones so I can emulate disks (somewhat important) and a TU77 > tape drive (really important). Tape is the big issue, as only the TU45 > and TU77 (maybe the TU16, I forget) are supported on a 2020 and both > require the extremely rare TM03 with the 18 bit fiddler (AI has one on > the TU77 there, but I don't think I want to ship my 20 out to Washington > to use it again :-) > > An emulator that could do an RM80/RP06/RP07 would be quite handy. If you > need someone to test it, I'd be happy to assist. > > CZ > > On 4/23/26 11:37, Jim Bender via cctalk wrote: > > > > Yes, there are simpler ways to approach the disk/tape storage problem, > > and for > > the most part it is already solved on 16 bit machines-- i.e., the > > unibus SCSI > > card plus a ZuluSCSI if you want to get away from spinning media > > entirely or > > perhaps a unibone. > > > > For 18 bit disks the situation is a bit more complicated, which is > > likely one > > of the reasons the original LCM Massbus emulator came into existence. > > > > The goal of this project isn't just to "solve" the disk/tape problem, > > it is > > also to be able to utilize a major hardware component of the systems > > that most > > people have avoided in recent years because of the unwieldy, > > power-hungry and > > relatively low capacity drives normally connected to it. > > > > For some systems, Massbus is a better way to attach storage than on the > > unibus, and on other systems the only really practical way. > > > > > > > > On 4/23/2026 10:08 AM, Chris Zach via cctalk wrote: > >> 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 H?lscher 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 &lt;cctalk(a)classiccmp.org&gt; 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 > >>>> > >>>> >