Digital Circuits/Encoders-Decoders

Encoders and decoders are similar to multiplexers and demultiplexers, except that they are a little bit more complicated.

Decoders

Decoders will have N inputs, and $2^N$ output. Let's say that we have two inputs (I1 and I2), and 4 outputs (O1 O2 O3 O4). Decoders will satisfy the following truth table:

I1	I2	O1	O2	O3	O4
0	0	1	0	0	0
0	1	0	1	0	0
1	0	0	0	1	0
1	1	0	0	0	1

Binary numbers come in, and essentially select which wire to send a signal on.

Encoders

Encoders work in exactly the opposite way as decoders, takeing $2^N$ inputs, and having N outputs. When a bit comes in on an input wire, the encoder outputs the physical address of that wire.

Encoders and Multiplexors

The relationship between the two.