Pravetz 8D

HARDWARE

Pravetz 8D is clone of Oric Atmos computer. It has:

64 K of RAM (in normal mode uses only 48K)
16K Rom
6502 processor (1 MHz)
Storage memory is tape recorder.
Soft reset : uses NMI pin of the processor.

FULL SCHEMATICS

This is not original schematis of the computer, but it is rewriten by entusiasts form working Pravetz 8D plate and published in our computer magazine in the end of 80's. So, may be there are mistakes. The schematics is here.

ROM

there are several rom images of the basic in Pravetz.
The original is: pravetzt.rom
You can use this rom like original Pravetz. If you wand disk emulation you need 8DControllerROM
and use CALL#320 command.
The modified ROM is: pravetzd.rom
You can use it only with disk controller.
It have some nice features:
- starts dos loading automatically (without need of CALL#320 command). But if you have not loaded disk it loops.
- have Cold Reset. So, if some program do the computer to not responding and Reset button of the bottom is not usable, you can use the real reset pin of the processor. In the usual rom it makes to restart computer and loose program in memory, but with this rom you can back to your program without loosing it. The price is: you haven't STORE and RECALL commands in Basic.
The author of the changes is Borislav Zahariev.

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 bassic 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.

GALERY

Pravetz 8D Face
Pravetz 8D Inside
The last Pravetz 8D - almost nobody have it. It has PC-like keyboard.
8DBook
Printer2PC controller - I used it to connect to PC and transfer programs. The bad new is that I have loosed the driver, and now I must write new one.