!11-PDP eht ni deppart m'I !pleH
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Today I  have got  a new  toy: the  Soviet pocket  computer Elektronika
MK-85M. I  already have a  bunch of Elektronika  MK-85 ones (and  a few
MK-90s, too) but I never had the precious MK-85M.

It is not very different, actually.  The only change is larger RAM (6kB
instead of  2kB of the  MK-85). But these two  extra chips made  it not
only  more  power  hungry  but  also much  expensive  (RAM  chips  were
expensive in the past).  Thus it was also much less  common. It was the
first MK-85M  which I ever  spotted on the  eBay (the MK-85s  are quite
common there).

So what it this "Elektronika MK-85M"?  It is a pocket computer which is
designed to look and function like the Casio FX-700p calculator. It has
the  same dimensions,  the same  keys and  its BASIC  interpreter works
almost exactly as  the BASIC of that Casio. But...  the Casio used some
simple CPU. Soviet engineers (from  the "Angstrem" company located near
Moscow) used a CPU which was easily available for them. It was the 1801
series CPU  [1]. These  CPUs ware  commonly used  both in  military and
industry. These CPUs were Soviet designs (they are not clones) but they
were compatible with the PDP-11 CPUs from DEC.

Thus it is a device which looks like Casio calculator but internally is
more close  to DEC's  minicomputers. The particular  CPU used  in these
MK-85(M) has some limitations, it can  address only small RAM (only 128
kB, I  think but it  was not so important  because RAM size  was mainly
limited by  available power source -  and batteries in 1980s  were much
weaker than today's ones). So the MK-85  machines had only one 2 kB RAM
chip and the MK-85M model has three these chips.

The  CPU can  run in  so-called  "turbo" mode  at  2 MHz  but then  the
batteries can be flat in few  hours. Thus it normally runs at something
like 0.5 MHz. It is still faster  than the CPU of the FX-700p (but some
functions - namely the goniometric ones  - in the BASIC interpreter are
done in  very ineffective way so  actual computation is slower  if they
are used). There  is also possibility to use external  power source and
then there is no problem with the "turbo" mode.

It is  interesting that it  is sometimes  stated that the  MK-85(M) was
produced from  1986 to early  2000s. Of course,  in later 1990s  it was
produced only  in small batches and  often only on a  special requests.
For example,  my machine has printed  1992 as a year  of production but
the  serial  number (which  is  pressed  into  the case,  not  printed)
includes also production  date which is 1995! (I assume  that they used
old cases with pre-printed date for a long time).

The device has some advantages over the poor old Casio (FX-700p is from
1982, the MK-85 is from 1985). Some of the design and software mistakes
were fixed (like the known exp() problem) and there is also added input
and output in the Russian alphabet. Also, the 10-segment liquid crystal
display can  be used not only  as alphanumeric one but  every available
pixel  can  be  addressed  individually.  So  some  crude  graphics  is
possible. There  of course are some  new bugs and -  more importantly -
the device pis much less durable  than the Japan-made Casio. The screen
protection pis from  a low-quality plastic material  but more important
is lower quality of some  connection between electronic components (the
main problem  is the  display connection). It  is interesting  taht the
keyboard is better  on the Soviet model (it has  better feedback and to
me it seems to be more durable).


And with so powerful PDP-11 in my  pocket I can even play the Prince of
Persia! Well, not exactly. There is a game written for the MK-85M which
somewhat looks like the Prince of  Persia but is of course much simpler
(still, it only fits to large RAM  of the MK-85M and it requires to run
the CPU in the  "turbo" mode). Now I have to find  the link and re-type
the game into the device.


References:

[1] gopher://gopherpedia.com/0/1801%20series%20CPU