PDP-11/05 (was: PDP-11/05 microcode dump?)

Tom Uban tom at figureeightbrewing.com
Tue Jun 15 14:16:35 CDT 2021

On 6/15/21 2:02 PM, Josh Dersch wrote:
> On Mon, Jun 14, 2021 at 10:34 PM Tom Uban via cctalk <cctalk at classiccmp.org
> <mailto:cctalk at classiccmp.org>> wrote:
>     On 6/14/21 3:39 PM, Noel Chiappa via cctalk wrote:
>     >     > From: Tom Uban
>     >
>     >     > it has the early version M7261E Control Logic & Microprogram board and
>     >     > the later version M7260 Data Paths board
>     >
>     > Ah, I'm glad someone found all that stuff I wrote up there useful. As always,
>     > I _think_ I got it all transcribed correctly, but do be on the lookout for
>     > errors!
>     I most certainly did - thank you for creating it!
>     >     > it seems like an older/newer combination, but maybe that was common. I
>     >     > would not have guessed that the four possible combinations would all
>     >     > work together, but maybe they do?
>     >
>     > I honestly don't know. As far as I can tell, the DEC documentation doesn't
>     > even _mention_ the two different board generations; perhaps a sign that they
>     > are functionally interchangeable? (Although even the section on baud rate, in
>     > both DEC-11-HKDBB-A-D and EK-KD11B-MM-001, 4.11, doesn't even mention the
>     > early board. So maybe the manual just ignores the earlier version completely?)
>     >
>     > I don't have an /05 up and running at the moment, or I'd check all 4 and see
>     > if they all work.
>     >
>     >     > Presently, the machine sometimes runs relatively well and other times
>     >     > it does not.
>     >
>     > What are the failure symptoms? (It's almost certainly going to take a 'scope
>     > to fix it; I expect you have one?)
>     I have KM11s, a scope, a logic analyzer, a unibone, shiresoft unibus analyzer, etc.
>     No shortage of gear, just a shortage of time.
>     > I'd start by monitoring the CPU clock, and make sure it's running when the
>     > failure happens. (Note that the front console is handled by the microcode, so
>     > if the microcode isn't running, the machine will be totally dead.
>     > EK-KD11B-MM-001 has a good description of how that works.)
>     I think I checked the clock when I started this project a while back, but I will
>     check it again. Unfortunately, I haven't figured out how to provoke two states,
>     but it mostly picks the completely dysfunctional state, so I'll look at the clock.
>     >     > my initial messing with KM11 boards, reveals that I can step the
>     >     > microcode with a KM11 in either the #1 or #2 position, but when two
>     >     > KM11s are installed at the same time, they do not function properly
>     >     > together. Is this expected or do I have an issue there too?
>     >
>     > Not sure. EK-KD11B-MM-001 (available at:
>     >
>     >   http://www.bitsavers.org/pdf/dec/pdp11/1105/EK-KD11B-MM-001_Jan75.pdf
>     <http://www.bitsavers.org/pdf/dec/pdp11/1105/EK-KD11B-MM-001_Jan75.pdf>
>     >
>     > and definitely something you need) says, at pg. 5-6 "KM11 switches have the
>     > same function in slots KM-1 and KM-2", and on 5-7 "permits the user who has
>     > only one KM11 to plug into either KM-1 or KM-2".
>     >
>     > So that _sounds_ like you should be able to plug two in together. The first
>     > indicates that the switches, the only input to the KD11-B from the KM11, are
>     > wired in parallel, and the only other thing on the KM11 are the lights,
>     > outputs. And why mention "user who has only one KM11", if having two is no
>     > use because one can't use two at once?
>     I've read that doc, but did not come away with the impression that both
>     can be used at the same time or not.
> Just to provide some real-world data, I used a pair of KM11's to debug my 11/05, see the picture here:
> http://yahozna.dyndns.org/scratch/1105-debug.jpg <http://yahozna.dyndns.org/scratch/1105-debug.jpg>
> They worked fine.  (These are clones, from Guy Sotomayor's kit.)  I can verify tonight whether I
> have the earlier or later rev CPU set, if that helps.
> - Josh
Interesting! From your pic, you have the M7260 without the circular baud rate selector switch, but I
cannot tell which M7261 board you have.

Does the machine come up and run normally with the boards in and the switches all the disabled
positions or do you have to do a special sequence to start?

I will have to look at the schematics to see how the two slots connect to the processor on each of
the board versions and maybe also take a look at Guy's KL11 schematic if it is on his site.


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