Elwro 800 Junior

In mid-80's, the Ministry of Education decided to introduce a Polish computer to schools. Of course it was too late, many bigger schools had ZX Spectrum computers or Timex ones, accessible a bit easier than Spectrum. Other institutions decided to go with MSX, more expensive computers but with disk operating system.
The new computer had to be cheap, ZX Spectrum compatible and able to be easy produced and repaired.
In 1986, Ministry confirmed Junior design, created by engineers from Technical University in Poznań, and directed it to production in Elwro factory, Wrocław.
The computer was cheap in manufacturing. Many components came from Elwro warehouses, already made for something totally different. For example outside case of Elwro 800 Junior is the case of "Elwirka" toy electronic piano, produced earlier by Elwro. The computer was cheap, but it had better capabilities than Spectrum.
Designers added a network based on serial communication, parallel port, floppy disk thru network support and support for CP/J operating system - a CP/M clone, designed especially for network appliances. In 1987 first units were shipped to schools. After lots of problems especially with network and floppy drives, computers became an useful aid in IT teaching.
In late 80's (or early 90's) another Junior computer has been designed, not only educational but full-featured home computer with built-in 3.5" floppy drive and RS-232 instead of Junet. Elwro 804 never came out of prototype phase.
Unfortunately, Junior was a bigger cause of Elwro's bankruptcy. During crisis times in late 80's it caused a debt - over 20% of yearly production.

Manufacturer Elwro

Origin Poland
Year of unit 1988
Year of introduction 1986
End of production 1989
CPU Z80A (MME prod.)
Speed 3.5MHz
ROM 24K (Basic, CP/J loader)
Colors: 8x2=16
Sound: Beeper
OS: Basic
CP/J (CP/M 2.2 compatible)
Display modes: Text: 32x24, 64x24
Graphics: 256x192


Media: Tape
External FDD if controller installed

Power supply:

Built in semi-switching power supply giving
5V DC at 1.5-2A, connected to M/B with 2 wires on the left.

I/O: Joystick connector
Spectrum network (rare)
Composite monitor
RGB monitor
Tape connector
Junet network
Disk drive connector (if controller installed)
Printer connector (Centronics)
Possible upgrades: FDD controller (dedicated)
FDD from PC.
Software accessibility: Dedicated: Almost impossible
Spectrum, CP/M software: easy.


I have a complete unit and a few not working mainboards of different revisions. There were 3 versions of this computer:
 - Elwro 800 - With no FDD controller and Junet network support
 - Elwro 800-2 - With Revision 2 / B mainboard, which was much better.
 - Elwro 800-3 - With FDD controller, and the best Rev. 3 / C mainboard.

Small school usually got one set of computers, larger ones got two.
A set of computers consisted of: 8 student's Juniors, without FDD controller, one Teacher's Junior, with FDD, one Mera D-100 printer, Neptun 156 display units for every computer.
Of course everything was done quickly and carelessly, so units came incomplete, damaged, or even not assembled. Manufacturer testing was simple: They put a program (memory R/W, CPU usage, graphics character juggling) in loop and left computers run it overnight. Next day, if it was still working - Test Passed. If it hanged, they performed one more 24h test. Maybe it'll work. After 2 or 3 unsuccessful tests computers were diagnosed and repaired. Now they passed tests.

JUNET was a serial bus network. It means that the computers were daisy-chained, forming a bus, if you disconnected one computer, all computers next to this point were disconnected from network. Connecting to network was performed by plugging 2 DIN plugs into the computer. Sockets are jumpered 1:1 inside. Network has 3 lines: Data, Clock and busy. It seems self-explainable what are their functions. Clock works at 14MHz/256, so transfer is about 55kbit/sec. Master computer gives clock to all slave ones. Input and output are connected with each other in Data line. All networking is done by 8521 USART. If you can't find 8251 inside your Junior, it's KP580BB51A. Soviet analog.

Network is used in CP/J, a CP/M clone with Junet network capabilities. If one computer uses the network, BUSY signal gives information that no other computer may use it.
Floppy disk can be divided up to 16 "private" sections, for reading/writing files and one "public" section, but read only.
After connecting Juniors in network and turning them on, user sholud boot CP/J at teacher's computer and use INSTAL command to define network. This configures computers' hardware addresses, quantity etc. Next, command JUNET is used to run a network. CP/J should be now broadcasted to all student's cmputers.
To use shared printer, PRINT command is used. Job queuing should work.
To send messages between computers, use MESS command.
If you noticed that I'm writing this using "should" and  "may" words, you should know that I've never used Junet, but Junet users told me that there were more unsuccessful tries with it than successful ones.
It is possible for teacher to capture student's screen, however, this may end with crashing student's computer first, teacher's computer after 3-4 seconds and finally killing a whole network.
 One more thing: Sending messages from teacher's computer to specified student's computer doesn't work in some configurations. Use 255 to broadcast.
The most common thing you can get from Junet is:

Błąd sieciowy.
Powtórz Zaniechaj Ignoruj:

It means: Network error. Retry Ignore, Fail:
If you see this, just reset everything. In many cases system will NOT work after this error.

Elwro 800-4 Junior PC was Elwro 800-3 Junior with home computer capabilities. It was Polish Commodore 65 - a legend, and only few prototypes survived. In first months of 2012 one unit has been sold in auction for 3400 Zlotys (~800EUR).
Differences between this and 800-3 are probably:
 - Default booting to CP/M mode (holding B during boot-up runs BASIC mode)
 - RS-232 instead of Junet
 - Fully Centronics-compatible printer interface.
 - Color TV modulator (in plans - no survived units have it)
 - 3 floppy drives support (with external 800-3 Junior floppy drive)
 - 720K 3.5" Floppy Disk Drive built-in.
 - BASIC mode supports printing with D-100M printer and serial port.
 - Spectrum emulation is slower than in Junior 9about 20% slower)
 - 2 floppies with software:
  > PC-Junior floppy transfer program,
  > REDJ document editor,
  > FRED word processor,
  > GRED graphic editor,
  > Optyka and Funkcje educational software (these two probably not used at all)
 - Ability to handle A: and B: floppy disks with one drive - with prompt to swap when needed, C: and D: reserved for external floppy unit, the same as in normal Junior.

Source: Bajtek, 1988

Junior in Infosystem '89. Src: Bajtek 1989

Junior in Infosystem '87. Src: IKS 1987

Early Junior with white keyboard -
Source: IKS 1987

Better photo of this unit (from Bajtek, 1986):

Junior with printer. Src: IKS 1987

Contents: Starting Making tapes, floppies Pinouts Emulation Links


It boots displaying a nice logo, with information about equipped hardware:
 - Wersja dyskowa - version with FDD controller
 - Wersja bezdyskowa - version without FDD controller.
This procedure ends and throws you into Spectrum mode. In this mode computer works quite like ZX Spectrum. Keys have ZX Spectrum meaning, it can load and run Spectrum software.
It should be possible to use disk drive in Spectrum mode using LOAD*, SAVE*, MERGE* commands. Listing should be done using DIR command, or DIR [drive no].

Loading CP/J:
Boot to Spectrum mode
Press Ctrl and release it.
Press Alt, then DOS. CP/J will pop on the screen.
Press Return (CR). It should boot the floppy.

Making system tapes and floppies:

Tapes are like in Spectrum. They are Spectrum tapes at all.
Disks are made like normal CP/M disks. In my filelend you'll find two programs: 22dsk142 is a DSK reader/writer for general CP/M disks. disks.zip contains some NOT VERIFIED software read by CPCDiskXP software, included in archive.

If you have Hungarian floppy disk drives with your Junior, for gods' sake, DO NOT USE THEM! It's the best way to destroy a floppy. Manufacturer replaced them months after release, so all drives should be good.





Video - nearly all Polish microcomputer displays have this connector:

1 - Luminance
2 - Ground
3 - Sound

And RGB output (D-sub 9 female)

1 - Ground
2 - NC or Composite sync
3 - Red
4 - Green
5 - Blue
6 - Brightness bit
7 - Sound
8 - H sync
9 - V sync


1 - Tape out*
2 - Ground
3 - Tape in

Tape out also goes to Spectrum Network middle pin.

Junet network

1 - Data
2 - Ground
3 - Clock
4 - Busy
5 - Reserved for future use (bridged inside)

Printer (Centronics), D-sub 37 pin female:

1 -   /STROBE
2 -   Data1
3 -   Data2
4 -   Data3
5 -   Data4
6 -   Data5
7 -   Data6
8 -   Data7
9 -   Data8
10 - /ACK
19-28 - Ground

Joystick, D-sub 9 pin male: Nothing more is known. It goes to 8255.

1 -   PA3
2 -   PA2
3 -   PA1
4 -   PA0
5 -   PA5
6 -   PA4
7 -   +5V
8 -   PA6
9 -   PA7

Floppy disk drive (DSub 37-pin Male)

Junior PC FDD connctr
1 -   /WREN
2 -   /LCT
3 -   /STEP
4 -   /DIR
5 -   /W DATA
6 -   /R DATA
7 -   /INDEX
8 -   /READY
9 -   /FR
10 - /HDSEL
11 - /TRACK0
12-13 - /HDL
15 - /SEL0
16 - /SEL1
19-27,29 - GND

31 - /RUN0
32 - /RUN1
36 - /WPROT
37 - /FAULT


10, Drive B
16, Drive B


It's possible to hook up the floppy drive, using pinout on the right half of the table. Drives must have DRIVE0 and DRIVE1 jumpers selected.





There are 2 emulators of Junior.
First, commercial one, has been made by Vulcan in early 1990s and it seems to, more or less, work under DOS. I have no idea if it was ever released widely or not.
Second one, available in my fileland too, is an open-source unfinished project, which I've never tried.
One of interesting things in this open source emulator is a ROM archive. This contains all ROMs, PROMs, EPROMs from the computer.
In my fileland, you'll find a 2.88MB bootable DOS disk image with pre-configured emulator to run on any virtual machine, which emulates VGA graphics. Why not conventional 1.44MB? Emulator comes with one floppy with CP/J, and during run it produces one more floppy image to put to drive 2. They are about 720K each, which fills conventional floppy.

To enter CP/J, use following combo: Press and release Ctrl, hold Alt and press Home key, release both. CP/J text should pop at the bottom of the screen. Press return.

This emulator doesn't emulate Junet at all. It hangs during start because of: a. one computer is not a network for it (or for OS broadcasting :) ), b. it doesn't emulate network interface.

PrintScreen key toggles to options.

Here I'm going to show a few screenshots from emulator. Click on a screenshot to see full resoultion.

This is a general view of the emulator. On second screenshot there's a Junior prompt.


This is a CP/J prompt and INSTAL networking program.


This is a Junet splash screen. During this screen original Junior sets network up and running.





If you think that you can find a software for it in the Internet, forget about it. Currently there's no software for Junior accessible.

http://sites.google.com/site/krzkomar/elwro-800-junior - Here (site in Polish) are some explainations, schematics and Junet protocol.
http://www.starekompy.pl/800.html - Description in Polish
http://8bit.yarek.pl/computer/zx.junior/index-pl.html - Here you'll find some dead file links and Junior's memory map.
http://www.aresluna.org/attached/computerhistory/articles/listyojuniorze - Letters about Junior - if you know Polish you can read about all problems with it.
http://web.archive.org/web/20040211175823/http://www.zxspectrum.it/other.htm - ROMs of Spectrum clones, including Junior.