Mera Elzab terminal board
This mainboard looks like a "newer generation" Mera
terminal mainboard, but has a few things different than in typical unit.
I have no idea what it was made for, as it has connectors not seen in
these terminals. There are keyboard and printer connectors, serial port
and CRT connector, like in all newer (one-board) Mera-Elzab terminals.
But there are a few other connectors which aren't frequently seen here.
First, is the LED connector, the same as in "independent monitors". But these one-board devices were usually "dumb terminals" called "dependent monitors". Another one is labeled "Podstawa" which means "Base". It was used to manipulate brightness/contrast in older terminals - in newer ones it was done right from CRT circuits, not through the mainboard or, in earlier units, by connector on solder side - wires won't fit between smaller new-generation chassis and mainboard. Maybe it was mounted in place of system bus board in older-generation chassis?.
To say more, Mera units were usually based on Z80 CPUs. This mainboard is based on 8080 CPU, made by Polish CEMI, and has a picture generator based on character ROM from CEMI too.
Power connector set is typical. It uses +35V to run CRT, and symmetrical 5 and 12V.
|CPU:||8080 (CEMI MCY7880)|
|Keyboard:||Unknown, parallel connection.|
|Main port:||Serial port (Ground, Rx and Tx only)|
|Additional ports:||"Base" Connector
Keyboard connector (parallel)
CRT display connector
Power connector set (+35V, +5V,-12V, -5V, ?+12V?)
Peripherals in collection:
|I have no idea about the exact source of this mainboard.
It was found in a pile of junk thrown from KFAP (Krakowska Fabryka
Aparatow Pomiarowych - Measurement Devices Factory in Cracow), along
with few other components from Mera Elzab (mainly dot matrix printers
guts). It looks like it was modified extensively. Maybe it was returned
after unsuccessful modification to order or testing?
I found it without any EPROMs and EPROMs you can see in
photos are blank parts from my collection. There was a dust on EPROM
sockets, which means that EPROMs were removed long ago. ROMs were only
components missing - CPU, character generator, even 6475 analog chip and
DIP switch were in sockets. One EPROM is in black socket, while another
one is in East German green one. Only the first one has corresponding
German 2114 ?"buffer"?.
Source: IKS 1987
Notice mainboards used there - they are like my one, but they contain white EPROMs instead of character ROMs.
The unit has 8080 CPU and 8228 bus controller. There's 8255 parallel interface to handle keyboard and 8251 serial interface to handle printer. Character generator is made around MCY7304 character ROM. Glue logic is made with Polish, Soviet or East German components. There are only few western logic chips. 4 2114 Memory chips are western too.
On the solder side there are many modifications with thin wires. It seems that someone tried to make this terminal do something other than it was made for.