Unibus disk controller with modern storage

Paul Koning paulkoning at comcast.net
Wed Oct 19 18:46:43 CDT 2016

> On Oct 19, 2016, at 6:48 PM, shadoooo <shadoooo at gmail.com> wrote:
> Hello,
> I read several posts about Unibus disk interfaces and emulation.
> One of my retrocomputing dream is to design an Unibus universal board,
> probably based on FPGA because of precise timing requirements,
> to emulate one or more disk/tape interfaces, and possibly something more.
> The real storage could be based on SD card, so very easy to be moved
> to a PC for imaging and data transfer.
> Probably a low level emulation would be quite easy, while a more complex
> solution (MSCP) could be more difficult.
> The board itself wouldn't be cheap at all, because PCB would be big,
> and because FPGA aren't cheap either.
> Probably it would be anyway cheaper than an MSCP-SCSI, and it would be far more
> flexible.

Actually, Unibus has very straightforward timing.  It certainly should be a breeze with an FPGA, but the original designs (nicely spelled out in the back of the early Peripherals Handbooks, or later on in the Unibus Handbook) take just a handful of MSI ICs.

Yes, a non-MSCP disk would be a good choice.  I'd suggest the Massbus series, they are just about as simple as anything and that's where you find the largest capacities short of MSCP devices.  And even an RP07 fits comfortably on a small SD card.  Or 8 of them, for that matter.  Apart from MSCP, avoid RL emulation also.

SD is actually the hardest part, at least the initialization.  If there's off the shelf IP that handles that state machine, the rest is simple.  Alternatively, is CompactFlash still around?  That's just an ATA interface, really easy.

How small is the smallest possible Unibus DMA card?  Quad, if I remember right, because of where the NPR/NPG wires live?


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