PPT - Encoders and Decoders Electrical Engineering (EE) Notes | EduRev

 Page 1


ENGIN112  L17: Encoders and Decoders October 10, 2003
Encoders and Decoders
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ENGIN112  L17: Encoders and Decoders October 10, 2003
Encoders and Decoders
ENGIN112  L17: Encoders and Decoders October 10, 2003
Overview
° Binary decoders
 Converts an n-bit code to a single active output
 Can be developed using AND/OR gates
 Can be used to implement logic circuits.
° Binary encoders
 Converts one of 2
n
inputs to an n-bit output
 Useful for compressing data
 Can be developed using AND/OR gates
° Both encoders and decoders are extensively used in
digital systems
Page 3


ENGIN112  L17: Encoders and Decoders October 10, 2003
Encoders and Decoders
ENGIN112  L17: Encoders and Decoders October 10, 2003
Overview
° Binary decoders
 Converts an n-bit code to a single active output
 Can be developed using AND/OR gates
 Can be used to implement logic circuits.
° Binary encoders
 Converts one of 2
n
inputs to an n-bit output
 Useful for compressing data
 Can be developed using AND/OR gates
° Both encoders and decoders are extensively used in
digital systems
ENGIN112  L17: Encoders and Decoders October 10, 2003
Binary Decoder
° Black box with n input lines and 2
n
output lines
° Only one output is a 1 for any given input
Binary
Decoder
n
inputs
2
n
outputs
Page 4


ENGIN112  L17: Encoders and Decoders October 10, 2003
Encoders and Decoders
ENGIN112  L17: Encoders and Decoders October 10, 2003
Overview
° Binary decoders
 Converts an n-bit code to a single active output
 Can be developed using AND/OR gates
 Can be used to implement logic circuits.
° Binary encoders
 Converts one of 2
n
inputs to an n-bit output
 Useful for compressing data
 Can be developed using AND/OR gates
° Both encoders and decoders are extensively used in
digital systems
ENGIN112  L17: Encoders and Decoders October 10, 2003
Binary Decoder
° Black box with n input lines and 2
n
output lines
° Only one output is a 1 for any given input
Binary
Decoder
n
inputs
2
n
outputs
ENGIN112  L17: Encoders and Decoders October 10, 2003
2 2- -to to- -4 Binary Decoder 4 Binary Decoder
° From truth table, circuit for
2x4 decoder is:
° Note: Each output is a 2-
variable minterm (X'Y', X'Y,
XY' or XY)
X YF
0
F
1
F
2
F
3
0 0 1 0 00
0 1 0 1 00
1 0 0 0 10
1 1 0 0 01
F
0
= X'Y'
F
1
= X'Y
F
2
= XY'
F
3
= XY
X Y
Truth Table:
2-to-4
Decoder
X
Y
F0
F1
F2
F3
Page 5


ENGIN112  L17: Encoders and Decoders October 10, 2003
Encoders and Decoders
ENGIN112  L17: Encoders and Decoders October 10, 2003
Overview
° Binary decoders
 Converts an n-bit code to a single active output
 Can be developed using AND/OR gates
 Can be used to implement logic circuits.
° Binary encoders
 Converts one of 2
n
inputs to an n-bit output
 Useful for compressing data
 Can be developed using AND/OR gates
° Both encoders and decoders are extensively used in
digital systems
ENGIN112  L17: Encoders and Decoders October 10, 2003
Binary Decoder
° Black box with n input lines and 2
n
output lines
° Only one output is a 1 for any given input
Binary
Decoder
n
inputs
2
n
outputs
ENGIN112  L17: Encoders and Decoders October 10, 2003
2 2- -to to- -4 Binary Decoder 4 Binary Decoder
° From truth table, circuit for
2x4 decoder is:
° Note: Each output is a 2-
variable minterm (X'Y', X'Y,
XY' or XY)
X YF
0
F
1
F
2
F
3
0 0 1 0 00
0 1 0 1 00
1 0 0 0 10
1 1 0 0 01
F
0
= X'Y'
F
1
= X'Y
F
2
= XY'
F
3
= XY
X Y
Truth Table:
2-to-4
Decoder
X
Y
F0
F1
F2
F3
ENGIN112  L17: Encoders and Decoders October 10, 2003
3 3- -to to- -8  Binary Decoder 8  Binary Decoder
x y zF
0
F
1
F
2
F
3
F
4
F
5
F
6
F
7
0 0 0 1 0000000
0 0 1 0 1000000
0 1 0 0 0100000
0 1 1 0 0010000
1 0 0 0 0001000
1 0 1 0 0000100
1 1 0 0 0000010
1 1 1 0 0000001
F
1
= x'y'z
x z y
F
0
= x'y'z'
F
2
= x'yz'
F
3
= x'yz
F
5
= xy'z
F
4
= xy'z'
F
6
= xyz'
F
7
= xyz
Truth Table:
3-to-8
Decoder
X
Y
F0
F1
F2
F3
F4
F5
F6
F7
Z