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P > PRAVETZ > 8D     


Pravetz
8D

The Pravetz 8D was a Bulgarian clone of the Oric Atmos featuring a Bulgarian version of the 6502 processor called CM630, 16 KB of ROM and 48 KB of RAM

The keyboard was almost the same as the original Atmos version, including a MK key, similar to the CTRL key, a C/L key allowing to display Cyrillic or Latin alphabets, and cursor keys. As in Pravets 82 (etc), the original lowercase characters were replaced by cyrillic characters and the C/L lock key, was the CAPS LOCK key of the Oric Atmos.

Like the original Atmos, The 8D had two modes of recording : Fast mode at 2400 bits/sec. and slow mode at 300 bits/sec.

The computer also featured a parallel Centronics interface and a user port. Pravetz provided a local dot matrix printer called "Petritch" but the popular Epson printers could be also connected to the 8D.

The "D" after Pravets 8 stays for "Äîìàøåí" (Domashen = For home use), and the idea was, that it should be used without having to buy any peripherals - monitor (which couldn't be connected through composite video to a Pravets 8D without modification) and FDD (cassete recorder used instead).

Floppy drives, modem and joysticks were also available. Floppy disk drives were very hard to find (in fact they appeared only in the early nineteens). They were a modification of the Pravetz 82 FDDs but with a built-in controller, making them two times bigger. Probably that was one of the reasons why Pravetz 8D never achieved the popularity ot Pravetz 8 (despite of the 3 times lower price).

There were in fact two ways to have floppy disk drives for the Pravetz 8D. One was indeed to use Pravetz 82 FDD and to develop an additional controller + power supply (the schematic and firmware were published in "Computer for you" magazine). There was an operating system called DOS 8D, developed in Bulgaria by Borislav Zahariev.

Later, Pravetz factory decided to develop special FDD for the 8D, which was bundled with the controller and the power supply in a box twice bigger than the normal Apple ][ floppy. It came out on market when the production of the computer itself was finished! It used also modified version of DOS 8D for DIY floppy.

The computer was very well crafted and the survived systems often look as new.

___________

Contributed to this page : Bozhidar Stefanov, Jordan, anonymous visitor

Peter Petrov reports:

ROM
There are several rom images of the basic in Pravetz. If you wand disk emulation you need 8DControllerROM and use CALL#320 command.

RAM
With Basic you have 48 K RAM to work, but with this little schematics you can use additional 16K. The signals that you need for proper work are these. One trigger is used to form MAP signal, but second is free to use additional thing. If you realise schematis of disk controller below you can use these schematics together to load 8DDOS v2.10 in additional RAM. You must use write operation in these adresses to use the controller:

#380 - writing in additional RAM - additional thing is off
#381 - writing and reading in additional RAM - additional thing is off
#382 - writing in additional RAM - additional thing is on
#383 - writing and reading in additional RAM - additional thing is on
for "additional thing" see Disk controller section

So, if you realise this little controller you can use:
FOR I = #C000 TO #CFFF : POKE I,0 : NEXT - clearing first 4K of additional RAM or you can move the basic interpreter in additional memory and use:
POKE #381,0
to go in RAM interpreter and make changes in it.

DISK CONTROLLER

If you have Apple ][ floppy drive and disk controller you can use this schematics to connect them to your Pravetz (Oric). The schematics is from two parts:
buffers
controller
The signals for proper work of the controller are here:
You can change the signal Q with changing the resistors of monovibrator 74LS123. The record of EPROM is here:
You must write it from addres #20 of the EPROM.

Connecting RAM controller and disk controller:
you can connect these controllers by this way:
pin 9 of 74LS74 is connecting to A8 addres bar of 2716 EPROM, so the "additional thing" is second page of the EPROM, where is the program of loading DOS 8D v.2.1 into additional RAM. (The record of the EPROM above is exatly for first and second page).

SOFTWARE

The versions of the DOS I have are:
Dos 8D v1.0 - you can use it if you realise only the schematics of the disk controller, but this versions loads in normal RAM, so it is unusable with long games.
Dos 8D v.2.1 - you can use it if you realise the two schematics and connect them. So - dos loads in additional RAM and you can use all the programs you have.
You can use regular Oric software in Pravetz 8D, but you have not regular letters. You have cyrillic letters instead. Changing of the keyboard maps is with Ctrl-T.
There are some games for Pravetz like SnakeByte, Tetris (exellent clone) and other. Most of them are from Bulgarian computer magazine "Computer for you". There is 80 column text editor, Disk copier program and the most beautiful - Borislav Zahariev ported BigMac Assembler from Apple ][ to Pravetz, so you can use if you realise schematics above. Soon I hope you will see this software here.

We need more info about this computer ! If you designed, used, or have more info about this system, please send us pictures or anything you might find useful.
ShareThis


 

This machine was perfect. I work on her in 1990 in
Physics faculty in Sofia. I think after 20 years she''s still working. New PC can''t live more then 5 years.
The old is better maked , but old. Sweet memories .

          
Monday 5th July 2010
Stanislav  (Bulgaria)

WOW !! Dimiter , do you have an emulator ? where can i find it ?

L

          
Friday 7th July 2006
luca (Italy)

This is my first personal computer. I even have an emulator for it. It works with TV/monitor and it has colors (I can't remember how much, but the games were colorful). I loved to play games on it, it works with cassette tape recorder instead of floppy. I learnt to program in Basic on it :)
It's TV Out was better than mine GeForce 2 LOL :)))

It was cheap low-cost solution to home users.
I gave it as present to my cousin before couple of years and I have to check will the games still run.

          
Friday 24th December 2004
Dimiter at lycos.co.uk (Sofia)
NN

 

NAME  8D
MANUFACTURER  Pravetz
TYPE  Home Computer
ORIGIN  Bulgaria
YEAR  1985
END OF PRODUCTION  1989
BUILT IN LANGUAGE  Basic
KEYBOARD  Full stroke 57 keys Qwerty + cyrillic
CPU  CM630 - Bulgarian copy of the 6502
SPEED  1 mHz
RAM  48 KB
ROM  16 KB
TEXT MODES  40 columns x 28 lines
GRAPHIC MODES  240 x 200 (+ 3 text lines)
COLOrsc  8
SOUND  Programmable Sound Generator AY-3-8912 (from General Instruments)
3 voices, 8 octaves + white noise
SIZE / WEIGHT  35 (W) x 25 (D) cm
I/O PORTS  Power supply, Expansion port, Printer/Centronics port, Tape-recorder DIN plug, RGB video out, RF TV out
POWER SUPPLY  Built-in power supply unit
PERIPHERALS  floppy disk unit, modem, dot matrix printer
PRICE  420 levs (Bulgaria, 1985)


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