# Dfiference between demux and decoder

1. Oct 29, 2005

### EvLer

could someone draw a clear distinction between these two for me? or are they basically the same?
Decoder usually takes several inputs (2^n) and produces n outputs. Multiplexer is a switch but demultiplexer....if it's inverse of multiplexer than it has to have at least several inputs but the simplest mux has only 1 output, which means that if it is used as demux, it has only 1 input.
Any clarification is greatly appreciated.

2. Oct 29, 2005

### exequor

I think a decoder takes n inputs and produces $$2^n$$ outputs. I know that it is possible to turn a decoder into a mux, not sure about a mux to decoder.

Last edited: Oct 29, 2005
3. Oct 30, 2005

### jsaxton

Let's clarify:
A decoder takes n inputs and produces 2^n outputs. An encoder takes 2^n inputs and produces n outputs.
A multiplexer selects one line from many lines. The inverse of selection is distribution. A demux essentially transmits data from one line line to 2^n possible output lines. The output line is determined by n select lines. In short, a multiplexer selects an input line, a demultiplexer selects an output line.

The differences between these two circuits is subtle, as far as I can tell. A demux simply selects an output line, nothing more. It's a glorified switch. A decoder takes n inputs, and uses those inputs to determine which of the 2^n output lines is high. This is the difference, I think. A decoder is designed to simply keep one line high. A demux is designed to set one output equal to the input (whether it be high, low, or a changing signal).

I'm just learning this stuff myself, so if I made a mistake, please correct me.