# Help about DTL Standard

Discussion in 'Homework Help' started by it_yashar, Aug 9, 2010.

1. ### it_yashar Thread Starter New Member

Jul 26, 2010
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HI
Can you help me about

How is the NOR gate 3 input in DTL Standard???????

2. ### Papabravo Expert

Feb 24, 2006
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I'm not quite sure what you are asking here. Nobody has used DTL since the 1960's so there might not be much information available on the net or elsewhere.

3. ### it_yashar Thread Starter New Member

Jul 26, 2010
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I mean how is the NOR gate in Diode-Transistor Logic ?

4. ### beenthere Retired Moderator

Apr 20, 2004
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5. ### Papabravo Expert

Feb 24, 2006
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In literal English your question is meaningless. If the NOR-gate was a living person the answer might be "he is feeling fine today" or "she is sad and unhappy".

I'm guessing that what you are asking is "How does a 3-Input DTL NOR Gate work?" If you follow the link in the previous post and add another circuit "C" identical to the ones for "A" and "B" then you have your 3-Input NOR Gate.

Operation depends on what the three transistors are doing. With nothing connected to the inputs you can see that each of the transistors is in the "ON" state because current will flow from the +5V power supply through the 4.7K pullup through the forward biased diode and into the base of the transistor. This will pull the output to ground. Exactly the same thing happens when an input is at +5V since in this case the input diode is reversed biased and only a small reverse leakage current will flow.

Connect an input to ground and current now flows from the +5V supply through 4.7K pullup resistor through the input diode to Ground and the output transistor no longer has sufficient base current to keep it in saturation and it goes to cutoff. With the transistor in cutoff the 1K pullup on the output makes the output go to +5V. One input by itself is not sufficient to allow the output to go high (+5V)

In order for the output to go high (+5V), all three inputs must be at Ground. That is the NOR function, did you follow that explanation?

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6. ### it_yashar Thread Starter New Member

Jul 26, 2010
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Is possible 3-Input NOR gate in DTL (Diode-Transistor Logic)????

If possible How is the gate circuits???

7. ### beenthere Retired Moderator

Apr 20, 2004
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From the previous answer posted -
If you want to make more inputs than three, simply keep adding inputs exactly like input "A" or "B" - so even 8 input DTL NOR gates are simple to construct.

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8. ### it_yashar Thread Starter New Member

Jul 26, 2010
5
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Sorry
can you show it in circuit ?

9. ### Papabravo Expert

Feb 24, 2006
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If you are asking about the availability of DTL Integrated Circuits or modules like the old DEC Flip-Chips (actually PC Boards with discrete components and some ICs) then I would have to say that finding something like this outside of eBay would be extremely unlikely. This technology was obsolete by 1972 when TI published an early edition of the TTL Data Book.

10. ### Ron H AAC Fanatic!

Apr 14, 2005
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Homework requires a little work on your part. You have been given a lot of information. What are you missing?

Feb 24, 2006
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12. ### Wendy Moderator

Mar 24, 2008
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That was a nice refresher course. Thanks guys.

I occasionally make diode resistor and DTL logic via components.