Encoder

It is a logic circuit which performs the opposite action of decoder.
An encoder has number of input lines, only one of which is activated at a time. At the output it displays a value corresponding to the activated input.
Encoder has 2ⁿ input lines and 'n' output lines.

2ⁿ : n encoder

2 : 1 encoder

4 : 2 encoder

8 : 3 encoder

4:2 encoder

Here, we took only when output is '1'