Decoder and encoder

Decoder

• What is a decoder

  • a decoder a combinational circuit that coverts binary information from n input lines to a maximum of $2^n$ unique output lines (minterms)
  • it outputs a high signal to the corresponding input value

x1	x2	d0	d1	d2	d3
0	0	1	0	0	0
0	1	0	1	0	0
1	0	0	0	1	0
1	1	0	0	0	1

• Enable input Decoder

  • There is an enable signal that enables an input

  • EX

    • you have only 2 8 bit decoders and you need to output a 16 bit, you can have an enable signal that disables the 0-7 one when the signal is 1

  • Enable pin

    • an enable pin is similar but we must use an and gat with last input so that way we can hand it off

  • EX:

    • to make a 16 bit decodre with only a 4 decoder we can use 5 decodres and use the output of the first one as the enable pin for the others
    • 

Encoder

• What is an encoder

  • The inverse operation of a decoder

  • it has $2^n$ inputs and n outputs
  • the output lines generate the equivalent binary number of the input line whos logic is 1

• WHY

  • we can use it as a signal detector, like when we have $2^n$ inputs and we want to see which service is being requested we can use it to display :)

• Encoder priority

  • If there is a priority input at the time it will output, because it has priority