Moscow Nights

Moscow Nights
=============

I have decided to try one of my Elektronika MK-90 [1] portable
computers. For a long time I had one special item in my "todo.txt"
file:

----------------------------
(D) +mk90 @test @code Try to play "Moscow Nights" BASIC example
----------------------------

As you may know, the Elektronika MK-90 is a USSR portable computer
which used a PDP-11 CPU clone. It has a liquid-crystal screen (120x64),
a full keyboard (with calculator-style keys), some 16 kB of RAM (but
just about 10 kB available for user) and a ROM of 32kB (the BASIC was
stored here) and two clots for "memory cards" (16kB each - there was no
another size but it is said that the card controller can support memory
chips up to 64kB).

The display can show 40x8 characters and also some graphics (black and
white only, of course). And there is also a communication port (the
only known use is to connect to a very experimental Elektronika MK-92
dock with integrated plotter and with the tape recorder connector).

The important thing is that the device has also a very simple beeper
which can be used to produce some noise.

So, it is a cute device which can run BASIC. It is a clone of an old
version of the DEC PDP-11 BASIC [2] with some commands added and some
others removed.

I even have an original printed manual with sample programs. One of
them is also a program which plays the soviet "Moscow Nights" melody
with use of the beeper (via the PLAY command). I always wanted to try
this one bud I never found time to code that. So this task was one of
the long-standing in my "todo.txt".

At January 1 I decided to code the program. It has only about 10
lines but half of them is filled with data for the PLAY command.
Surprisingly, it worked... The result can be found on my Phlog page. IT
is not pleasant but it somewhat resembles the melody... It was recorded
with use of a simple microphone and the IRIS Indigo.

If you are curious how the MK-90 works: the keyboard is not nice
(similar to calculators or to the HP 2000LX keyboard but its quality is
lower) and the screen font is big (and thus ugly). But shortcuts for
most of BASIC commands are available on the keyboard (there was ever a
transparent keyboard overlay available to have them on hand).

The bad thing is that there is no BASIC command to write data/files to
storage devices (and also no command to read such data). Interactive
input is of course available and there is also the DATA statement.

The device has also some commands to save, read, edit, delete and copy
files (but the files are expected to be BASIC ones, with number at the
beginning of each line).

It is good to remember that MK-90 was not a finished product: only some
1500 pieces were produced, the BASIC 2.0 was only available on a data
card (there is probably no actual MK-90 with the BASIC 2.0 in the ROM)
and most of expected add-ons were made. For example, the device has
commands to print on a printer but there is probably no such printer.
The only know thing is the MK-92 dock which requires to use memory card
with an updated BASIC (the 2.0) and it is very rare.

Anyway, it is one of a few portable PDP-11 clones (the Elektronika
MK-85 is even smaller - it's a calculator with the PDP-11 CPU).

References:

[1] http://www.pisi.com.pl/piotr433/index.htm#mk90
[2] http://bitsavers.trailing-edge.com/pdf/dec/pdp11/basic/DEC-11-AJPB-D_PDP-11_BASIC_Programming_Manual_Dec70.pdf
[3] gopher://gopherpedia.com:70/0/Moscow%20Nights