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

Jay Logue jay-cctalk0092 at toaster.com
Mon Jun 14 10:37:29 CDT 2021

I also have an 11/05 with the early CPU boards that exhibited stuck bits 
on arrival.  Turned out to be bad transistors in the inhibit circuits on 
the G110.  Pretty easy fix once I tracked it down. So far I've found the 
GT40 print set to be a fairly accurate, at least for the boards I have.

I'll be curious to learn how your serial console works.  Mine had a 
manufacturing defect that had to be corrected before input would work.


On 6/13/2021 1:44 PM, Tom Uban via cctalk wrote:
> I am working on the first of my two 11/05s. Interestingly, it has the early version M7261E Control
> Logic & Microprogram board and the later version M7260 Data Paths board (with circular baud rate
> selector switch) as described in:
> http://gunkies.org/wiki/KD11-B_CPU
>  From the description there, 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 have a couple different drawing sets for the 11/05 and while some have the matching M7260
> schematic, only the GT40 drawings (I found on bitsavers) has the M7261E schematic:
> http://www.bitsavers.org/pdf/dec/graphics/VT11/GT40_Graphic_Terminal_Engineering_Drawings_Feb73.pdf
> The GT40 drawings has the PROM listings and related, so I am hoping that they match what is in the
> two boards.
> Presently, the machine sometimes runs relatively well and other times it does not. It does have bit
> 1 stuck ON in memory, but that should be a relatively simple task to diagnose as it is not
> intermittent. When the machine is "working" I am able to deposit 0777 at 0100 and run. When running
> this simple program, I've experimented with flexing the boards and such, so it doesn't seem like an
> obvious poor connection, but that remains to be seen.
> The machine is a configuration #2 model (as described in the "gunkies" site) and 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?
> Thanks much to those who have provided details and documents on the web, they have already been of
> great value and will most certainly continue to be a resource in the future.
> More updates in the future...
> --tom
> On 5/6/16 5:32 PM, Noel Chiappa wrote:
>>      > From: Mattis Lind
>>      > Thanks Noel for sorting this out.
>> Eh, de nada. But thank you.
>>      >> I wonder if the ucode in the two versions is identical? The uROM chip
>>      >> numbers should give it, (if they are the same on both versions, albeit
>>      >> in different locations on the board), but I have yet to check. Does
>>      >> anyone happen to know?
>> OK, so the situation here is pretty complicated. To start with / make things
>> worse, that CPU uses lots of PROMs. Lots and lots and lots and lots of PROMs.
>> For the data paths board (M7260), both major versions appear to contain the
>> same PROMs (going by the DEC part numbers), but the chip location (Exx)
>> numbers are all different.
>> For the control board (M7261), the C, E ('early' version) and F ('late'
>> version) etch revisions each contain mostly the same PROMs, but apparently
>> with slight differences between the sets of PROMs in each (as reflected in
>> different DEC part numbers). For details see:
>>    http://gunkies.org/wiki/PDP-11/05#Control_PROMs
>> to which I have just added all the gory details.
>> As to getting the contents of all of them dumped in machine-readable form -
>> oi vey!
>>      >> on the earlier version (prints for that version are in the GT40 prints
>>      >> online
>> It turns out that I have hard-copy prints for the "C" etch revision of the
>> M7261, which do not yet appear to be online; the GT40 prints have the "E"
>> etch revision.
>> I will scan the pages for that revision of the board, and put them up 'soon'.
>> (I'm not doing the whole print set, it's about 1" thick, and most of them are
>> for other things anyway, like MM11-L memory, etc.)
>> 	Noel

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