One of the first microcomputers made in Poland,
Meritum was TRS-80 Model 2 based computer. Designed in 1983, it was
manufactured in Mera Elzab - factory, which produced electronic
Unfortunately, it was not popular. First, it was too slow, considered obsolete even before introduction. More, it has no graphics mode - only alternative character set to draw tables, and first version had no floppy disk drive support.
In 1985 Model 2 was released, which had a floppy drive support and could be tailored to customer's needs - RAM could be expanded to 32 or 48kB, serial port could be changed to needs. Unfortunately it was still obsolete computer, with almost no compatible software in Europe, so its popularity wasn't big. Moreover, because Hungarian and Bulgarian floppy drives were not good, so engineers quickly decided to use better drives from East Germany. It was a big mistake, because East Germany factory was falling behind with dispatching orders for internal computer factories! This lead to higher import duties and higher prices of floppy drives. And Meritum half-switching power supplies, they heated a lot and burned quickly.
So, if executives can wait half a year and buy Spectrum with Microdrive or Timex with FDD, and enjoy existing big software library, OR they can buy a Meritum in 2 months, but for more money and with almost no software (with floppy disk drive - if lucky), it was quite obvious that the first option was better.
Meritum was also rejected as an educational computer, because of its lack of graphic modes. Instead of it Elwro 800 Junior was introduced.
|Year of unit||1986|
|Year of introduction||1983/85 (Model 2)|
|End of production||1988 (1987)|
|CPU||Z80 clone (U880D)|
MER-DOS (in Floppy, Model 2)
CP/M (in Floppy, Model 2)
|Display modes:||Text: 32x16, 64x16
Graphics: Semigraphics with alternative character set.
External FDD connector (Model 2)
|Possible upgrades:||Not much known, Memory to 64K, but I don't know how about addressing. Some internal components can be upgraded by adding pre-made boards.|
(a Meritum logo)
My unit is a prototype of network unit. It has a small
board with a few logic chips applying the simplest re-make of serial
port into network port, similar way to Elwro 800 Junior network. It has
a network-extended Basic, written in OETO and Silesian Technological
University. Its logical unit number 5 is hard-coded into ROM. Network
extension can be launched by typing NET - a menu pops up which allows to
work in network, shared floppy, message and program broadcasting,
terminal mode etc.
There's known another network interface, put to parallel port. It's external one.
There were a 3 versions of Meritum:
The most unusual applications of this computer were:
In December of 1987, "Gazeta Robotnicza" ("Workers'
The name Meritum comes from concatenation of Mera (producer) and ITM (Innowacje, Technologie, Maszyny - Innovations, Technologies, Machines) - a joint venture company.
Some other notes:
You can emulate Meritum in MESS by using ROMs stored in meritum and meritum_net folders in MESS ROMS directory. Emulation is bad. In net version cassette writing routines are bad, my unit, which uses the same ROMs works well with cassette, emulated unit produces unreadable WAV files. Keyboard emulation is unstable. But it works.
|Contents:||Starting||Making tapes, floppies||Pinouts||Monitor||Links|
In many ROM revisions it asks first about memory to
reserve. It can be: "MEMORY SIZE" or in Polish: "OBSZAR PAO". The last
word here is abbreviation of "PAmięć Operacyjna" - RAM. Press Return to
Some very rare units are modified to boot MER-DOS or CP/M Disk operating system. This means that it has no BASIC in ROM, it has only code to boot system from floppy. If it can't boot, it'll display error and jump to monitor built instead of BASIC.
Currently (2011) there's no emulator of it. There's no dedicated software on the Internet. The only programs you can get are type-ins from Polish magazines Bajtek, Informik etc., they're quite accessible (search for RetroReaders forum, but it may change).
The biggest problem with this computer is its unstability with graphics juggling. To check if your computer is affected, test it with this program:
30 FOR I=0 TO 2000
40 SET (RND(127),RND(47))
50 NEXT I
60 GOTO 20
If it hangs while operating graphics, the first reason
is unstable power supply, Next, check memory. The glue logic isn't
usually a problem except beige Soviet chips, they are likely to fail in
More information about type-ins in Machine code. Most type-ins in machine code work well in Meritum I, but fail in Disk Meritum (Meritum II or Meritum I Model 2) - it is because USR command is handled different way. So in Meritum I it was:
POKE 16526,A : POKE 16527,B
Meritum II allows to define a few USR machine code programs, so it will look like:
You may also encounter some problems with parsing hex data.
More information in Polish:
- Uruchamianie Mikrokomputera Meritum, Piszemy program w Meritum Basic, Niskorozdzielcza grafika Meritum - from "Mikrokomputer w szkole i w domu", K. Socha. (Starting Meritum microcomputer, writing programs in Meritum Basic, Low-resolution Meritum graphics)
- Komputery osobiste w Polsce - from Kuryłowicz, Madej, Marasek - "Komputery Osobiste" (Personal Computers in Poland)
- Meritum - opis języka BASIC - from Frelek B. "Mikrokomputer - Programowanie w języku BASIC" (description of Meritum Basic)
Currently (2011) noone in Poland bothers about this
computer, so there's no known method of archiving its software. Because
some disks are probably in CP/M like format (MER-DOS is not much
like CP/M, but it was possible to run CP/M on some Meritum), CP/M disk
archiving methods may work. Another disks and tapes may be in
TRS-80 like format, so simply putting them to universal CAS file should
do the job.
Meritum tape interface is 500-baud one, so low CAS tape images may be playable.
In my fileland, there are some utilities to read TRS-80 disks and tapes, and to convert high/low baud tape CAS files.
Meritum is a bit copied from TRS-80 Model 2, but I don't know for sure is it program-compatible (it was one of design assumptions, but maybe engineers abandoned it?).
Commands for loading/savinf are CSAVE "NAME" and CLOAD "NAME".
To verify use CLOAD?, it'll show "BAD" on screen if finds an error.
If you type CLOAD and hit return, it'll load the first BASIC program it'll find. During loading two symbols (usually asterisk or rhomb) appear on the upper right corner of screen. Loading is good if left one lights steadily and right one blinks.
Loading machine code programs: Type SYSTEM [return] to get to the system mode, now type the first letter of program's name, hit Return and play the tape. If you don't know name, you can try or make Meritum display it. Displaying procedure has been described in Polish Bajtek Magazine, probably about 1986, but it doesn't work with my Meritum.
If a cassette played from PC doesn't work, try to invert waveform, for example in CoolEdit or Audacity. It may do the trick.
The software I recovered from my tapes (it's in fileland
in software directory) - currently there's only one small BASIC program.
It adds 3 options, which may be turned on or off by poke'ing memory:
- Keyboard auto-repeating
- Short beep after key pressing
- Disabling BREAK key.
By the way, there were 2 types of cassettes distributed
- With blue printed label and text in 2 lines - these were original ones, distributed with first units.
- With gray label, made on copier, text in 1 line (example) - these were cheaper, distributed with later machines.
Video - the male DIN5 plug comes with a "tail" from case. It can be hidden in computer's case, but I don't recommend it. It fits into Neptun 156(b) monitor well.
|1 - Composite out
2 - Ground
3 - Sound*
5 - +12V direct from power supply (not in all units)
* - first versions had a speaker built-in in keyboard PCB.
Serial port, in my unit it's Network port:
(by default it's 1200b/s, but it could be modified to order in 150 - 9600b/s)
|1 - RTS
2 - Ground
3 - TxD
4 - CTS
5 - RxD
|1,4 - Tape out (from computer)
2 - Ground
5,3 - Tape in (to computer)
Parallel and Floppy port:
The only thing I could get is an 8255 connection to parallel/floppy connector. According to Technical Operational Manual, Centronics, IRPR and Logabax interfaces require a special adapter.
|1 - PB3
2 - PB2
3 - PB5
4 - PB6
5 - PA4
6 - PA2
7 - PC5
8 - PC2
9 - PC3
10 - PA0
11 - PC0
12 - RESIN
13 - 0V
|14 - PB0
15 - PB1
16 - PB4
17 - PB7
18 - PA6
19 - PA7
20 - PA5
21 - PC4
22 - PA3
23 - PA1
24 - PC1
25 - +5V (0.1A)
There's a diagnostic edge connector on a mainboard. No idea what pinout it has.
It's an undocumented feature of Meritum Model 1 - in Model 2 there's
no monitor, its space contains FDD access routines. It's the last 2kB of
14K ROM, BASIC takes only 12K.
To enter Monitor program, use:
Now you're in Monitor mode. There are 7 commands. All parameters in
- D addr1, addr2 - displays memory from addr1 to addr2
- T addr1, addr2;k - tests memory from addr1 to addr2 k times
- M addr, d - Browse mmeory from addr. D is not required, but if we enter it, we can change byte to d. ENTER goes to next byte. Dot exits this mode.
- PW addr, d - Write data d to port addr.
- PR addr - read from port addr
- X r - Display CPU registers, if r applied, it's register name (A, F, C, D, E, H, L, M - (HL), S - (SP), P - (PC)), and the register can be modified.
- E pc., addr - Jump to procedure which address is stored in P register or address addr, if applied.
- POLISH - Monitor explained.
http://web.archive.org/web/20120821231753/http://www.elwro.zafriko.pl/kat/mikrokomputery/mera_elzab_meritum_i - General description
http://web.archive.org/web/20071110041320/http://www.e-service.net.pl/sumpirowicz/nfsk/komputery/meritum1.html - Some interesting photos.
http://web.archive.org/web/20080217064926/http://www.e-service.net.pl/sumpirowicz/nfsk/komputery/meritum2.html - More photo thumbnails.
http://kupazlomu.ovh.org/kolekcja/merameritum2.htm - Brief description in Polish.