BEMZ Byte (Байт)

This Spectrum clone has been manufactured in BEMZ - Brest Electromechanical Plant in Brest, currently Belarus. When it was designed in late 1980s, it was USSR, and mass production started around 1990. It was produced after dissolution of USSR, probably until mid-1990s (?1996?), now in Belarus - when it stopped to be useful as computer, it was still well usable as game console. Bajt (Byte) is a ZX Spectrum clone made on TTL chips.
The biggest difference between Bajt and Spectrum is the keyboard - here it's like a PC keyboard with quite well-working keys. Additional arrow keys have been moved to the rightmost block, where a dynamic speaker is also located. The dynamic speaker is used because the sound synthesizer of Byte is different than in Spectrum - in Bajt there is a 3-channel 8253-like timer chip working as a 3-channel generator. Additionally, a Kempston joystick interface is built-in with some buttons connected to additional keys.
The video is displayed through an RF modulator working on SECAM system or RGB output, sometimes with 7-pin and sometimes with 5-pin DIN socket. Another functional difference is presence of two character ROM sets - one is a ROM with Cyrilic characters while another is with Latin. Usage of these ROMs can be switches using keyboard. Additionally, there are two Spectrum ROMs, one like original one and another with messages translated to Russian. Switching between them is done by a button located on the right side of computer (near Reset switch). The processor, being a Z80-clone, was either Soviet or East German, while EPROMs were western. Memory has been implemented like in Spectrum, but using Soviet single-voltage chips (in earliest units there were even damaged 64kbit chips used like in Spectrum or multi-voltage chips).
The power supply unit supplied with Bajt was a heavy, transformer-based unit giving 12V at 1A (a bit less than 1A may be needed) and 5V on a few amps... give it good 3A, there's no ULA there but lots of TTL chips.
This computer's mainboard is designed like military equipment, which was also made by BEMZ. Very strict design rules have been used - there can be only horizontal and vertical tracks with really single exceptions of short 45-degree bends. Because there are around 80 integrated circuits and many discrete components inside (SECAM colour coder made using them), the mainboard has 8 layers of tracks. These times in Poland, a freshly implemented technology had problems with 3-layer boards (and PC AT-clone had to be composed on 2 layers only). Manufacturing of these was definitely not cheap. Later, a more professional unit has been developed - Byte-01 with 128kB of RAM, CP/M capability and tower-like floppy disk drive.
 

Manufacturer BEMZ Brest

Origin Belarus / USSR
Year of unit 1991
Year of introduction 1989/90?
End of production 1994?
CPU Z80
Speed 3.5MHz
RAM 48/80kB
ROM 16kB
Colors: 16
Sound: 3-channel synthesizer chip
OS: Spectrum-like BASIC
Display modes: Text: 32x24
Graphics: 256x192
 
 

Media: Tape Recorder

Power supply:


4-pin male connector at the computer

1 - +12V 0.5-1A
2,3 - GND
4 - +5V 2,5A

(This is NOT a Molex-like plug! voltages are NOT like in a PC!)
I/O: Expansion slot
Kempston joystick
Tape in/out
RGB out
RF out (channel 4)
 
 
 
 
 
 
Possible upgrades: Not much known
 
Software accessibility: Quite easy (Spectrum)
   

History of my unit is not known. I bought it form an ad as in unknown state, was working. The power supply unit is not original, but is probably from the set, as it's a bit older Soviet unit.

 

Contents: Starting SCART Pinouts Links

Starting, power:

Generally works and behaves like Spectrum in quite high degree, starts with a beep and emits clicks with speaker when buttons are pressed. To use Cyrilic letters, use RUS (ПУС) key, to go back to Latin - LAT. Russian ROM can be switched on with a button "СОВМЕСТ" on the right side.

The power connector can be made using an old Molex plug, but be careful about voltages - they are REVERSED so don't plug directly an AT/X power supply, modify a connector before. I have successfully modified a Molex connector, but it required some modifications:
1. The power wires - 5V and 12V are NOT like in PC, they're reversed.
2. The notch has to be a little larger. I sticked pieces of plastic to make the connector fill the hole entirely.
3. Holes for pins have to be a bit smaller (squeeze them in plug a little). If not -> no 12V, no starting.
4. A small piece of plastic may be needed in one hole if connector is a bit loose - the pitch of Bajt's connector is not exactly like AT. This piece of plastic pushes the metal part towards ground parts.

About tapes, this is like Spectrum and many Speccy games will work.
 

SCART connector

UNTESTED!
There are two versions: With 5 and 7 pin RGB connector. Usually 7-pin version has audio output and intensity signal on additional pins. The intensity allows to display "Bright" colours, but its downside is that it can display "black with intensity" and this IS visible as something like "dark grey".

DIN5 (7) pins

SCART pins
1 (Sync) 20 (Sync)
2 (GND) 5,9,13,4 (4 for audio)
3 (B) B (7)
4 (G) 11 (G)
5 (R) 15 (R)
6 (Audio) 2,6
7 (Intensity)  -


Schematics of various connections can be found in this site: http://zxbyte.ru/byte_connection_to_tv_and_monitors.htm (in Russian). The problem with Intensity-based connection is that it allows to make black+intensity (looking like a bit brighter "black" :) ). This needs some logic.

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Pinouts

Video pinout:
There are 5-pin and 7-pin versions - 5-pin have no Audio output and Intensity signal is not present.
Pin Function
1 SYNC
2 GND
3 B
4 G
5 R
6 Audio OUT
7 Intensity

 

Cassette port pinout:
1 - Output
2 - GND
3 - Input
4 - Output?
5 - n/c?

 

Joystick port pinout:
1 - Up
2 - Down
3 - Left
4 - Right
5 - NC
6 - Fire
7 - +5V
8 - GND
9 - NC

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Links

http://zxbyte.ru - This is a very good site about Byte computer. In Russian and English. Technical and other information.
http://zxbyte.ru/download.htm - Download documentation, ROMs and software
http://zxbyte.ru/byte_connection_to_tv_and_monitors.htm - Connecting to TV using SCART, also 7-pin version.
http://speccy.pl/articles.php?article_id=35 - Article about this computer in Polish
https://archive.codeplex.com/?p=zxmak2 - ZXMak2 emulator, can emulate Byte with ROM and RAM, so many original Byte programs can be run.
http://www.bemzbrest.by/ru/component/content/article/166-history-in-years.html - History page of BEMZ (yes, they exist today!) mentionong that Bajt manufacturing has been started in 1989, in 1990 they started serial production.
 

 

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