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| Full Adder on a breadboard |
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| David Hess:
--- Quote from: intabits on December 16, 2019, 10:57:38 am ---Have you considered DTL rather than RTL? I've always thought that the former was supposed to be be superior, though I can't justify that statement just of the top of my head right now. (No more complex than RTL? Better logic level integrity?) --- End quote --- RTL has lower noise margin. When integrated, it takes up more space than the alternatives. I have thought about doing a logic project using discrete transistors to implement integrated injection logic which takes more transistors but fewer resistors than RTL. |
| intabits:
--- Quote from: David Hess on December 16, 2019, 04:24:30 pm ---RTL has lower noise margin. --- End quote --- ^ the words I was looking for when I said DTL has "better logic level integrity", and also that DTL can handle many inputs easily (better fan-in) |
| intabits:
You may be able to save some transistors in your adder (and other compound circuits) by using 2 levels of diode logic. Looking at P20 of 223-2618_DDTL_Component_Circuits_CEMI_Sep1963.pdf, linked to above:- Diode logic AND-OR, and OR-AND can be used (but not AND-AND or OR-OR) with just one transistor. Once again, I haven't dug into the nitty gritty of this, so I'm just throwing it out there. It may be that this is only possible because of the dual supplies, and oddball logic levels that IBM used. |
| intabits:
How about a full adder using just 6 transistors? By choosing logic elements to avoid NANDs, the ANDs feed to the inputs of NORs, which allows 2 level diode logic, thus eliminating the need for some transistors. The Carry output inverter might also be eliminated by some bodge of the NOR to make an OR. (Emitter follower or PNP transistor?) Timing diagrams:- LTSPice schematic attached. To run the simulation, the logic equivalent circuit can be deleted, or the library it uses can be installed as described in:- |
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