Robotron K1840 .. (11/780 alike..)

Holm Tiffe holm at
Sun Sep 27 05:27:08 CDT 2015

some people from the "Rechenwerk Halle"
..a bunch of people that is interested in historical computing got an
Robotron K1840 DEC 11/780 clone lately and they try to get it running
again. (freinds of mine).

Unfortunately a thing called SKR Busadapter (Massbuss adapter) and the
entire console computer are missing.

So far as I know is the main CPU 100% compatible to the DEC original
using an UNIBUS System, PCBs are exchangeable, but the Console Computer
is not.
In The K1840 this is a K1620 Computer, the CPU is build from 8 Bit NMOS
slices (U830) and ordinary EPROMs (
using a mechanical different PCB System. The same system was used in the
K1630 PDP11-alike (see below) which had an MMU (K1620 has none).
The Main difference that's preventing unpatched OSes are the U834 Bus
interface ICs, that must be software configured before the devices can be
accessed from the QBUS-like System Bus. The U834 are containing the Bus
drivers and all needed registers for interrupt and DMA and the entire
address decoder logic needed for QBUS Systems which simplified the
interfaces somewhat.
Nevertheless of that progressive design, it was the worlds slowest PDP11..

In the K1840 ordinary TEAC FD55FV Floppies (2x) where used for the console
System to boot up the system.

So far so good (or bad).

There are a few things that I want to know now..

I know that in the original 11/780 the Console CPU was an 11/03
with some interface to load the VAX Microcode in to the main CPU.
Do you think it is possible to use an ordinary 11/23 instead?
What Floppy Controller was used in the original, I know that there was a
single 8" floppy drive in the 11/780 and don't think that the controller
was the usual RX01 or RX02 System...?

That's an article from the german magazine C't about the people which got
the K1840:

That's the K1840 on the left:

and The K1630 .. PDP11 not so "clone" on the right.
I don't think that the Tape drive was shipped with that machine, the
bulgarian original looked different so far as I remember..

Is there someone that would help out them with missing hardware/software?



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