Paul Koning via cctalk wrote:
>
>
> > On Mar 13, 2025, at 7:36 AM, Holm Tiffe via cctalk <cctalk@classiccmp.org>
> > wrote:
> >
> > ...
> > Ok, this is a full fledged mainframe CPU.. not really what I want todo
> > first.
> > That stuff tends to "explode" in sight of parts, needed power and space,
> > I know that.
> > On the other side I saw different controllers for PDP11/VAX stuff that
> > used the 290x to control "hardware". That are microprogrammed computers
> > w/o any system bus and macro-instructions. Even the controller of an DEC
> > RX01 RX02 is build around two AM2901.
>
> I can think of several places where DEC used 2901 designs. One is the VAX
> 730. One of the PostScript laser printers also used these, I think -- LPS20
> perhaps? Not the LPS40, that was a microVAX running VaxELAN based firmware.
The FPU's of PDP11's and the VAX11/780 used them too. As far as I
remember there where 16 pcs of 2901 on the FPU board. (Sorry, I only
know the boards of a east german copy of the 11/780, the Robotron RVS
K1840). The terminal multiplexers even had some AM2901, don't remember
how many for now.
After the fall of the iron curtain DEC hired all (!) employees from
Robotron Dresden "I'ts is a masterpeace of knowldge to copy an VAX11/780
with only a reference machine at the hand.."
I was one of the last administrators of the two K1840 fom our University
in Freiberg, east germany. The TU Bergakademie Freiberg is the oldest
university of mining and metallurgy in the world.
We ran those puppies an MUTOS 1800 (4.3BSD), not SVP 1800 (VMS).
The AMD29xx Chips in those machines where soviet products.
>
> Another, and an interesting one, is the UDA50. It has a 16 bit engine using
> 4 2901s plus a 2910 sequencer. My mentor Anton Chernoff worked on the
> microcode for it and showed me some of it. I remember it had a specialized
> assembler where the ALU opcode (for the 2901) was in the left half of the
> line, and the sequencer opcode (for the 2910) in the right half, separated by
> a semicolon. The 2901 had condition codes, which were transferred to the
> 2910 for conditional branches, but with a one cycle delay at least in the
> UDA50. So you could see weird stuff like this:
>
> clr r1 ; bne foo
>
> because the conditional branch would act on the condition codes set by the
> preceding line's ALU part.
>
> The UDA50 had an implementation, in a tiny amount of microcode, for a small
> 16-bit microprocessor instruction set. I think it was roughly a very much
> simplified PDP-11. That was used for various downloadable diagnostics and
> service tools, like a disk formatter. Richie Lary of PDP-8 fame wrote that
> part of the microcode.
>
> paul
>
Yes. There was AMDASM as an example (CP/M based).
But today every macro capable Assembler should do the job. It is only
about defining the function codes of ALU and Sequencer in Macros..
Regards,
Holm
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