Re: Which company is MFR90073? (Manufacturer of TTL chips in 1981)...

Erik Baigar wrote:
> The second remaining unknown is the 214/020. Here I still have no
> guess.
Did more measurements on this one and investigated the circuitry
around these chips. Now it is quite obvious: The 214-020 is a 
input frontend containing 5 diodes and 5 pull-down resistors. 

I put a summary on all these custom chips on my web page at: 
http://www.baigar.de/TornadoComputerUnit/PECchips/PECchips.html

On the 214-020, the common pin is connected to ground and the 
resistors act as pull-downs. The input signals of the unit 
are applied to the diodes which ****ft the level 0.7V towards
ground and the unit is listening to the junction between diode 
and resistor. Thus the combination increases noise resistance 
of the inputs and acts as pull-down...

   Thanks for all comments...

       Best regards,

          Erik.