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In my digital design module involving HDL (Verilog) and a ton of RTL diagrams, our lecturer always said never to use demultiplexers because they do not exist.

Why is that?

Michel Keijzers
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AlfroJang80
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    Please provide some context for this statement, such as a citation for an article. It would also be helpful if you could show the specific HDL code that you were told not to use. – Elliot Alderson Oct 08 '18 at 14:04

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Demultiplexers/decoders are commonly used in SSI/MSI logic because it's a convenient way to get an array of AND gates with various combinations of true and inverted inputs in a single package. (Example)

But that's really all they are. In FPGA design, each AND gate gets synthesized directly, sometimes combined with other functions into a single LUT. There's no particular reason to use a "demultiplexer" in the source code — it's more likely to obfuscate the design rather than making it clearer.

Dave Tweed
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  • Fantastic! I'm sorry I don't have more info on this. I just was revising HDL and I remembered this from a previous module. – AlfroJang80 Oct 08 '18 at 15:30