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I came across a page which explains bipolar transistors which are used to implement wired-and logic. It says

Another feature of DTL is its ability to implement a "wired AND" function. For example, if we wired several DTL NAND gates together, we would observe the following behavior. If any one of the NAND gates had a logic 0 as its output, the whole output function would also be at a logic 0 voltage. All the output functions would have to be at logic 1 for the output to be 1. See Figure B.9, which shows the internal wiring and the equivalent logic schematic for the wired AND function.

enter image description here

Looking at the figure, I see that, it all inputs (three gate inputs) are logical 0, then the output is logical 1 due to the pullup resistors. On the other hand, if any of the inputs (or all) is (are) logical 1, then the output will be zero because there is a connection between output and ground. So, it it actually implements wired-nand!

Any explanation for that?

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  • \$\begingroup\$ Um. It's a NOR, not a NAND. Or it is an AND with inputs not'd. Perhaps that's what they meant in using the preceding NAND gates? Or perhaps the conclusion might also be, "don't attend the University of Utah's Engineering department?" I really wouldn't get too caught up in it, myself. As Feynman wrote, "You should, in science, believe logic and arguments, carefully drawn, and not authorities." You know what is going on. That's enough. \$\endgroup\$ – jonk Feb 14 '17 at 7:44
  • \$\begingroup\$ The description and the diagram are correct. It is the "wired" function being described, which is as in the diagram Output = X Y Z. It is incidental that DTL gates in the illustration are NAND gates (or unknown gates represented by a single output transistor), they could have been any type of gates. \$\endgroup\$ – rioraxe Feb 14 '17 at 8:08
  • \$\begingroup\$ @rioraxe: If x=y=z=1 then the output will be . So, is that really AND function?! \$\endgroup\$ – mahmood Feb 14 '17 at 8:26
  • \$\begingroup\$ @mahmood: your comment is missing something. Anyway, if and only if X=Y=Z=1 then the output will be 1. That is really an AND function. \$\endgroup\$ – rioraxe Feb 14 '17 at 18:00

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