Difference between Demultiplexers and Decoders

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Rohitchampion

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Can anybody please explain exact difference between demultiplexers and decoders? I know difference is very subtle, but I am not getting exact difference. They are listed as decoder/demultiplexer in manufacturers' catalogues; so is their functioning exactly same?
 

The differences aren't so subtle. Why not try using Google and Wikipedia first?

https://en.wikipedia.org/wiki/Decoder
https://en.wikipedia.org/wiki/Multiplexer (see 2nd figure)

basically the decoder has a select input which "selects" one of n outputs to be active.
a demultiplexer does the opposite of a multiplexer and uses the select input to select one of the n outputs to have the value on it's input.

Regards,
 

ads-ee said:
basically the decoder has a select input which "selects" one of n outputs to be active.
a demultiplexer does the opposite of a multiplexer and uses the select input to select one of the n outputs to have the value on it's input.

Regards,
Click to expand...

Thanks for your reply ads-ee. And obviously I tried google before posting here.
Demultiplexer also has select inputs. If you see 2-to-4 line decoder and 2-to-4 line multiplexer, aren't they exactly same? So can they be used interchangeably every time? (because in manufacturers' catalogue also they are listed as decoder/demultiplexer as i mentioned before)
 

You should look carefully at the logic diagrams.

there is no data input on the decoder. A 2-to-4 decoder has 2 select inputs and 4 outputs. Each output is enabled based on the selects

a 1-bit 2-to-4 demultiplexer has 2 select inputs 1 data input and 4 data outputs.

You can force a demultiplexer to behave as a decoder if you tie the data INPUT pin of the demultiplexer to a logic high. That doesn't mean they are interchangeable. In a demultiplexer not hooked up as a decoder the input will show up on the output selected, so if the input were to toggle from low to high and then back to low the selected output will also toggle L-H-L. (the other outputs will be L).

Regards

Truth tables:
demultiplexer


decoder
 
Last edited:


Hi Rohitchampion

Decoders simply shift a bit entire of the out put pins ( shifting a o or just a 1 )
Demultiplexers just set the out puts according to the command pins and inlet signal . that's all .

Best Wishes
Goldsmith
 

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