Didaktik Gama

It was a small Czechoslovak home computer. First, engineers in Didaktik Skalica (company known of producing teaching aids) tried to make an old Tesla PMD-85 computer faster and better. First two versions of Didaktik were clones of Tesla PMD-85 Intel-based computers with better hardware and keyboard - because small keys in PMD were too small to do any serious thing.
Didaktik Gama was the first clone of ZX Spectrum in Didaktik series, but it was equipped with 80kB of RAM switchable by manufacturing-selected address. It was really hard to get this computer - first units had to be sold to schools, desperately looking for something better than constantly overheating PMDs. More, it was very expensive - more expensive than Delta (nothing to do with Didaktik naming, just Czech rebranding to avoid western embargo) ZX Spectum Plus. Why so expensive? First, manufacturing was very slow and gave many damaged units (which were diagnosed and fixed or working components were desoldered to be mounted in another unit). Second thing was a parallel interface (8255) inside and more memory. In Eastern block, you could use Soviet or western memory circuits. Soviet ones needed extensive testing before they were accepted, because some got errors shortly after manufacturing, western ones were more expensive, but tests could be avoided.


Manufacturer Didaktik Skalica

Origin Czechoslovakia (Slovakia)
Year of unit 1989
Year of introduction 1987
End of production 1992
CPU Z80A
Speed 3.5MHz
RAM 80K (16+32+32K)
ROM 16K (BASIC)
Colors: 8
Sound: 1-bit speaker
OS: Basic similar to Sinclair.
Display modes: Text: 32x24
Graphics: 256x192
 
 

 

Media: External Tape recorder  

Power supply:

Female 5-pin DIN at the computer:
1 - +5V DC (1A)
2 - Ground
3 - Audio INput
4 - +12V DC (200mA)
5 - Audio OUTput (read further!)

I/O: Parallel interface
Expansion system bus
RF modulator
Monitor output
Tape recorder socket (with power socket)
 
 
 
 
 
 
Possible upgrades: Some (from Spectrum) known.
 

 

 
     
Software accessibility: Difficult (A few sites, but ZX Spectrum programs work)  

My unit has been traced to private buyer, not a school.
Personally, I like its case and ergonomy of keyboard - big, visible square keys with documented functions. Unfortunately as you press the keys it's not so good - you don't know you pressed it or not, it doesn't go deep into the unit.


Didaktik M

Next Didaktik was more reliable and advanced computer, with a new case and keyboard with separate arrows. It had only 48K of memory (64K installed, but last 16K not accessible), smaller than Didaktik M, and had no parallel interface. Instead of it, engineers added Kempston and Sinclair joystick ports, but their pinouts were not compatible with anything.
Technically, engineers tried to make Didaktik cheaper. Instead of expensive ULA circuit they used Soviet Angstrem Т34ВГ1 (export version labeled ULA1) substitute, giving slightly different picture than in ZX Spectrum (aspect ratio was closer to 1:1 instead of 4:3). This circuit, tested in Kompas / Компас computer, had better thermal cycling stability than ULA, but only in DIP package - SMD version had poor thermal design, giving many internal thermal expansion forces prying connections from chip module.


Manufacturer Didaktik Skalica

Origin Czechoslovakia (Slovakia)
Year of unit 1992
Year of introduction 1990
End of production 1992
CPU Z80
Speed 4MHz
RAM 48kB (64K installed)
ROM 16K (Basic)
Colors: 8
Sound: 1-bit speaker
OS: Basic (Sinclair-like)
Display modes: Text: 32x22
Graphics: 256x192
Display a bit different than in Speccy - Soviet Angstrem used instead of ULA chip.
 
 

 

Media: Tape recorder
External FDD (thru system bus)
 

Power supply:

7-pin DIN female at the computer:
1,6 -  +5V 1A DC
3,7 -   +20V 200mA DC
2,5 - Ground.
 

I/O: Expansion bus
Sinclair Joystick
Kempston Joystick port
Monitor output
RF out
Tape connector

 
 
 
 
 
 
 
Possible upgrades: Not known
 

 

 
     
Software accessibility: Difficult (a few sites, Spectrum software works)  

My unit comes from school. It has been used so much that letters on keys are worn out. Moreover, its Angstrem is in plastic-molded SMD case, so the computer has its caprices - it sometimes hangs or changes colors. A light knock in case, near Angstrem restores a good situation.


Contents: Starting Revisions Connecting Peripherals Links

Starting:

These are almost Spectrum computers. They behave like Spectrum, so everything is like in Speccy. These computers should run many Spectrum programs well.

Tape creating is also like in Speccy.
 


Revisions:

There were a few revisions of Didaktik Gama computers.
 - The first one, black, called Gama '87, was so buggy that it had problems running Spectrum software.
 - Gama'88 - Engineers thought that 87 was buggy - it was not buggy, the Spectrum was! They had to solve problems to preserve these bugs, making Spectrum software run on Didaktik.
 - Gama'89, with many modifications and improved compatibility.

Didaktik M:
 - Model 90 - First model with ROM nearly the same as ROM 91.
 - Model 91 - With better keyboard (but still hard to type fast) and ROM 91, not sold for long time.
 - Model 92 - Model 91 with major changes in ROM (ROM 92). I have this version.
 - Model 93 - the last ROM, some small improvements. Last 92 models had this ROM.

Didaktik had always 16kB of ROM memory. In my unit they used a 27256 32kB ROM with upper half empty. I have no idea what is the goal of using more expensive memory chips whose areas are are left unusable, maybe to make future patches easier.
 

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Connecting peripherals.

If you know Czech, download docs from my fileland.
 

Tape
Didaktik Gama is small, so tape connector is integrated in power connector. Pinout in computer is as follows:

1 - +5V DC
2 - Ground
3 - Tape Input (from tape)
4 - +12V DC
5 - Tape output (to tape)

And you put a DIN plug with 2 cables to the computer (middle one). Last DIN is for tape recorder:

2 - Ground
1,4 - Input from tape
5,3 - Output to tape

WARNING! Some power supply models have Input/output pins reversed! Why? Because Tesla manufactured tape recorders with reversed pinouts in DIN (?Model TP-210?).  Even more, some have 5V on pin 5, but they're really rare and have additional wire to 2-wired cable. Better check your own with ohmmeter.

In Didaktik M  "MG" tape recorder socket pinout is:

2 - Ground
1 - Output to tape
3 - Input from tape

Joystick:
Didaktik Gama has Kempston Joystick interface built-in in a strange way, connected to the parallel port. You need to make an adapter and put it to parallel connector:


 

Parallel port of Didaktik Gama:

1  -  A0
2  -  A1
3  -  A2
4  -  A3
5  -  A4
6  -  A5
7  -  A6
8  -  A7
9  -  B0
10 - B1
11 - B2
12 - B3
13 - B4
14 - B5
15 - B6
16 - B7
17 - C3
18 - C2
19 - C1
20 - C4
21 - C5
22 - C7
23 - C6
24 - GND
25 - IN0
26 - OUT0
27 - IN1
28 - OUT1
29 - IN2
30 - OUT2

System bus connector is NOT 100% compatible with Spectrum. Generally, pins are similar, but 9V, -5V and 12V are missing, as video and some color signals. More, ROMCS signal is derived not from ULA, thus its electrical parameters aren't stable as fast as it should be. So, connecting ZX Interface to Didaktik Gama will probably make collision on the bus and may even damage computer. Read further to get pinouts.

In Didaktik M you can connect Sinclair or Kempston joystick to the computer, but you have to use adapters, because connectors are non-standard.


You won't find this A/B numbering probably nowhere except schematic :).

Number Sinclair Kempston
1A Ground Ground
2A Keying Cut Keying Cut
3A Right Right
4A Down Down
5A Fire Fire
6A NC Activate
1B NC NC
2B Keying cut Keying cut
3B NC NC
4B Left Left
5B Up Up
6B NC Activate

To get the computer know that Kempston is connected, connect Activate links together in plug.
 

Expansion bus of Didaktik M and didaktik Gama changes in green:

1A A15
2A A13
3A D7
4A NC
5A Keying cut
6A D0
7A D1
8A D2
9A D6
10A D5
11A D3
12A D4
13A /INT
14A /NMI
15A /HALT
16A /MREQ
17A /IOREQ
18A /RD
19A /WR
20A /ROMCS-D (nc)
21A /WAIT
22A /NC
23A /NC
24A /M1
25A /RFSH
26A A8
27A A10
28A NC
1B A14
2B A12
3B +5V
4B NC
5B Keying cut
6B GND
7B GND
8B CLK
9B A0
10B A1
11B A2
12B A3
13B NC (/IORQGE)
14B GND
15B NC
16B NC (Y video)
17B NC (V video)
18B NC (U video)
19B /BUSRQ
20B /RESET
21B A7
22B A6
23B A5
24B A4
25B ROMCS
26B /BUSAK
27B A9
28B A11

One more thing about these edge connectors. They are not protruding from board, they're just on the board. I've never connected anything to it, but I think you can use some edge connectors from, for example, old floppy drive, ISA slot or telephone operator's device, cut its sides and use a mechanized piece of plastic put instead of 2 pins for keying. I don't know will it be OK, I've never tried it!

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Links:

I hope that you stand Czech language, as many pages are in Czech.

http://z00m.speccy.cz/ - Some Didaktik files
http://didaktik.xf.cz/ - The most interesting part is game downoad archive (HRY).
http://www.8bit-museum.de/pcb/index.htm?group=35&id=185# - Didaktik PCB images.
http://www.volny.cz/holcapek/miraclesoft/didaktik.html - OK, here is a brief description of Didaktik line... in Czech.
http://zx.interface1.net/clones/didaktik.html - The older version of above description in English.
http://web.archive.org/web/20090624131919/http://electronics.mysteria.cz/gama192cz/index.htm - A Didaktik M clone.
http://mts.speccy.cz/  - Look in "Dokumentace" - docs for Didaktik floppy drive. There's also pripojene (connecting) of Centronics printer. Yes, in Czech.
http://cygnus.speccy.cz/ - Description of many Didaktik peripherals. In Czech.
http://trtsoft.profitux.cz/didaktik/didaktik.htm - Another site about Didaktik M. In Czech.
http://www.fi.muni.cz/usr/jkucera/pv109/2002/xmichal5.html - An extensive article about history of Didaktik computers. Yes, Czech too :).
http://www.youtube.com/watch?v=OiOtSrkYJNY - Didaktik Gama TV advertisement clip.

 

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