[cctalk] Re: Massbus emulation

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 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 >>> >>>