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Real-life NOT Gate?

  1. Dec 24, 2011 #1
    How does a NOT gate works in a genuine circuit? Like in a calculator?

    Thanks in advance,

  2. jcsd
  3. Dec 24, 2011 #2


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    Staff: Mentor

    A NOT gate turns a logic level of 1 into a logic 0, and vice versa. This can be used when a circuit that operates by receiving a logic 0 has need to be operated by a logic 1, for example. A NOT gate is typically the smallest and fastest gate, because with semiconductor circuits it requires the fewest components, so it can also be used as a buffer, and to sharpen signals that are not as digitally clean as some circuits need. A clean digital signal should be logic 0 or logic 1, and not waver around somewhere in between.
  4. Dec 24, 2011 #3
    But how would it work? I mean, a line powered with 1V with a inverter (or NOT gate) in it's path would turn the signal to it's opposite value, which might be 0V, am I right? But how this same inverter would turn 0V into 1V?
  5. Dec 24, 2011 #4
    Consider a single transistor in common-emitter configuration. When you put high on the base, transistor opens and pulls down voltage on the collector to 0. When you put low on the base, the resistor between collector and vcc pulls the voltage up to vcc.
    The real world circuit in a calculator probably uses two MOS transistors:
    where the low signal opens the top transistor and results in high signal on output, and high signal opens the bottom transistor and results in low signal on the output (during transition, very briefly, both transistors are open)
  6. Dec 24, 2011 #5
    Ohh I think I got it... It's definitely not how I expected though... Thanks :)
  7. Dec 24, 2011 #6
    Now that you have your answer, I have two more for you!!!

    1) What is a none gate?.................A gate that can accept all logic levels, no propagation delay, when you put in a 1, you get 0, if you put in a 0, you get 0.!!!!

    2) What is a WOR.......Write Only RAM?!!!...................A RAM that have infinite storage locations, you can use any logic levels, you can write as fast as possible.

    And yes, I invented these two!!!!

    Is this out of line even for Christmas Eve?:rofl: :rofl: :rofl:
    My big party is tomorrow, I just spent the whole day cooking and setting up the place. Getting a little wacky even with no alcohol!!!

    Merry Christmas

  8. Dec 24, 2011 #7

    jim hardy

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    i remember the "write only memory" well - signetics i think.
    only IC ever with pins for filament voltage, note 6.
    definitely from our era...

    http://www.national.com/rap/files/datasheet.pdf [Broken]

    http://www.national.com/rap/Story/WOMorigin.html [Broken]

    merry christmas to all,,

    old jim
    Last edited by a moderator: May 5, 2017
  9. Dec 24, 2011 #8
    I did not know that, that was before my time!!!!
  10. Dec 25, 2011 #9
    1) I think you are referring to the false gate, which will output 0 (false) no matter the input.
    2) Whaaat??
  11. Dec 25, 2011 #10
    Oh yeah... The old times...
  12. Dec 25, 2011 #11
    Then call it your invention!!!!

    Merry Christmas.
  13. Dec 25, 2011 #12
    Noo hahaha, I just said I didn't understand the second question and that the first one might be the false gate.

    Merry Christmas to u too :D
  14. Dec 25, 2011 #13
    You mean the write only memory? As Jim called it WOM, you can write anything in, but can never read it back!!!!!
  15. Dec 25, 2011 #14
    How would it work? Plus, how can it be used?
  16. Dec 25, 2011 #15
    Merry Christmas!!! We are all joking!!!
  17. Dec 25, 2011 #16
    That's a joke. It's when you have nothing connected to the memory bus. You can do writes, but you can't read anything out. A pun on the read-only memory which can only be read but not written, the write-only memory can only be written to, but not read. Sometimes external devices function as 'write only' memory - e.g. you can connect the LED here and make it blink when you write 1 to this address. It is actually common to treat output operations as memory writes, many CPUs lack any specialized output ports.
  18. Dec 25, 2011 #17

    jim hardy

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    As the article linked says, Signetics placed that WOM datasheet in the April issue of a design magazine as an April Fool's joke, for marketing goodwill. I was a young engineer at the time and it sure appealed to me....

    to original poster - google "7404 hex inverter", better yet buy one and experiment....
  19. Dec 25, 2011 #18
    The software implementation of write-only memory was invented by programmers long ago.

    On VMS it was a device called NLA0:

    Any write to this device succeeded immediately. It always read a null string or EOF depending on the mode it was opened with.
  20. Dec 26, 2011 #19

    jim hardy

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    ahhh DEC gear? A programmers dream.

    i detest those Intel swapped nibbles.
  21. Dec 26, 2011 #20
    You all can't do that with me, i'm just a newbie!!! XD
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