Decoder

A decoder is  logic  circuit  that energizes a particular  output line for each  combination of input  signal.

Fig   shown  the block  diagram  logic diagram  and function table to a 3 to 8  binary  decoder 74LSI138. This particular  decoder  sends a low signal  to one  its output  lines  (Y0-Y7). For example  if the input A, B, C,  lines  at logic 1, similarly if  input combination in 110 ( equivalent to 6.)  the out put line Y6 goes  low.