On Wed 16 Jan Brent Hilpert said: I am using discrete diode-transistor logic; I'm just trying to figure out what a sensible Vcc should be. I've seen discrete transistor logic designs with Vcc voltages from 3.6V clear on up to 90V, plus and minus (and often both). I suspect the higher voltages were more out of habit from vacuum tube days, but perhaps there were other reasons. Since I'll ultimately run this whole thing from batteries, I would naturally prefer to deal with 6V or 12V (or even 3V or 4V, depending on the battery chemistry), less the <mumble> dropout voltage of my regulator. So far I've been able to keep everything in the ALU data path to a depth of two diode gates. I'm using the complementary outputs from three flip-flops for true and inverted versions of the A-word and B- word bit streams and Carry inputs to the adder. It takes more gates this way, 25 diodes but no inverters, versus 12 diodes with two inverters.