Encoder is a kind of multiplexer having multiple outputs depending upon the number of input lines. Encoder has 2^n input lines and n output lines. The n output lines generate the binary information depending upon 2^n input lines. Consider the example of 8-to-3 encoder which have eight input lines and three output lines. The truth table of the encoder is shown in figure. The eight input lines would have 2^8 = 256 combinations. In this case only eight of all 256 combinations have the binary information the remaining
are 'don't care'. Figure shows the combination logic circuit of 8-to-3 encoder.