On the 370165 and the 36085 4011

KR Williams

ECL. Unless I'm mistaken there was no other way to get high speed at that time. "Mecl 10K" was used in mid 1970's but for the project I mentioned the later faster series was used; one chip manufacturer calling it "100K".

IBM used a 4.25 volt differential to operate its ECL, but the Rest of the World needed 5.2 volts for all but simple Or-Nor gates. This meant, when add-on people needed to modify an IBM mainframe, an extra power supply was needed ... unless the logic could be built from Or-Nor's. (And-Nand's had transistors in series so needed the extra volt.)

I don't understand this. We added 90 or 50 ohm resistors at the ends of any lines longer than 12 inches or so (IBM's 370-145 used 90-ohm impedance wires, the 168 50-ohm impedance; I don't remember why the difference.)

The Mecl parts lacked the current for *two* 50 ohm resistors, so on an occasion where two long lines were driven, one of our engineers showed us how to avoid signal "ringing" by terminating a line with two diodes instead of a resistor.

James