Construct 2:4 Decoder circuit with the help of IC74139 (74xx139)

ericgibbs

Joined Jan 29, 2010
11,551
hi cik,
Welcome to AAC.
Consider S1 [A1] and S2 [B1] as address bit inputs to the 74139.

So by setting bits S0 and S1 high or low, you can have 4 combinations.

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AAA 890 12.27.gif
 
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ericgibbs

Joined Jan 29, 2010
11,551
hi cik,
Downloaded your doc.
Lets talk you thru it.

Can you explain to me what you think the difference is between a Multiplexer and a Decoder [De-mux] ?

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ericgibbs

Joined Jan 29, 2010
11,551
hi c,
Your description is OK.
Have a look at this marked up, Demux, image, see the A and B [ Address select pins]
Note: in the 74139 there are two separate Demux's, we are just using one.

If A and B are Low, then Y0 output is enabled, if I now toggle [ swicth Hi/Lo] the Y0 will follow the Enable / G Input.
Do you follow that OK.?

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Added a 2nd Image

BTW
: It is important understand the Selected Output is Active Low
 

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ericgibbs

Joined Jan 29, 2010
11,551
hi c,
In your question paper equipment they include a 74139, are you allowed to use that on your Breadboard. ?, or do they expect you to build a 74139 equivalent using the NAND gates.?

Can you confirm.?

  1. Equipment
    • Breadboard
    • One 7400 quad two-input NAND gate
    • Three 7420 quad four-input NAND gate
    • One 74153 Multiplexer
    • One 74139 Decoder / Demultiplexer
 

ericgibbs

Joined Jan 29, 2010
11,551
hi c,
The X in logic table means 'it does not care, it can be either High or Low, '1' or '0'

Next time I am over there I expect a nice Kandil simidi ...

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djsfantasi

Joined Apr 11, 2010
7,187
Im now ok with that but please i wanna ask one more question for this first part: on the truth table for this example, what does it mean "X" ? does it mean like I should cahgne to 1 or 0... (I attached its truth table below)
“X” means don’t care. If the other inputs are as specified in the truth table, it doesn’t matter if the input listed as “X” is a 1 or 0.
 

djsfantasi

Joined Apr 11, 2010
7,187
...So now for the second part which is about IC74139, still i couldnt get it how can I do... (Im sorry for that)
What do you mean by “about 74139”? Have you read the 74139 datasheet?

I’ve linked to it above... Note that logically, the 74139 is equal to a 74LS139. They have slight electrical differences that won’t affect your problem.
 

djsfantasi

Joined Apr 11, 2010
7,187
Ah i meant the IC74139 one. Just image that you are in ur 1st class the university and ur teacher gave this thing during the lecture of Digital Circuits and Systems. So, still im not completaly capable to read the datasheet of the chip to understand for making the desing of it via https://circuitverse.org/ simulation website... Im really sorry for that but im trying to understand and listen yours carefully
But did you try to read it? Parts of it are very clear. Such as the table @ericgibbs provided. If you don’t try and wait to be spoon fed, it will be difficult for you to learn. Sheesh, all you had to do is click on the link I sent you, skim through, and you would have seen that table. But you waited for someone to spoon feed you. Maybe that’s what your professor is trying to teach you. To be self reliant and find the information you need by yourself.
 

djsfantasi

Joined Apr 11, 2010
7,187
I'm sorry to disappointed you. You are right and I must work harder for my failure
I’m assuming that it’s the problem of a translator you use or the possibility that English is not your native language.

Failure is too harsh an English word to describe a student’s mistake. It wasn’t failure. It was a mistake.

We all make mistakes all of the time. Particularly students, because they are expected to make mistakes. Failure comes when we don’t learn from our mistakes. It sounds like you have learned, so you did not fail.

We have a saying. You must learn from your mistakes, other wise you are doomed to failure!

Keep learning! You will do well.
 
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