MSCP - was Re: Unibus / Qbus

Paul Koning paulkoning at
Mon Oct 24 07:51:04 CDT 2016

> On Oct 24, 2016, at 7:39 AM, allison <ajp166 at> wrote:
> On 10/22/16 6:05 PM, Toby Thain wrote:
>> On 2016-10-22 4:08 PM, allison wrote:
>>> ...
>>> FYI I have never heard of any one recreating the RQDX1/2/3 software
>>> protocol MSCP
>>> as it was nontrivial, proprietary, and copyrighted.
>> It's been implemented in simh, afaik. Its reputation is a little more imposing than the reality.
>> ...
> That may be so but putting it on a board to accept a IDE drive is far more useful to us that run hardware.
> Why IDE, It can use CF and I also have a large supply of drives from 20-512mb.   Fortunately I have a
> large supply of MFM drives and two SCSI controllers for the larger supply of SCSI drives.  However, I
> feel I'm the exception and many Qbus users are not so fortunate.
> Where is the source code to for that? That is the drive side of that.

There's pdp11_rq.c.  If you were to do a bus interface with microprocessor behind it for the protocol work, that code could be adapted for the job.  And that would be the obvious way to build an MSCP controller -- that's how MSCP was designed to be implemented and how it was done in DEC's controllers.  A BeagleBone Black or the like would be more than ample for the job, given that early implementations such as the UDA50 were done with 2901 bitslice engines (and very odd looking microcode).


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