DECODER
&
ENCODER
1
2
DECODER
• Adecoder is a combinational circuit.
• A decoder accepts a set of inputs that represents a binary
number and activates only that output corresponding to the
input number.All other outputs remain inactive.
• Fig. 1 shows the block diagram of decoder with ‘N’ inputs and
‘M’outputs.
• There are N possible input combinations and 2N output
combinations.
• For each of these input combinations, only one output will
be HIGH (active) all other outputs are LOW
• Some decoder have one or more ENABLE (E) inputs that are
used to control the operation of decoder.
BLOCK DIAGRAM OF DECODER
DECODER
3
A0
A1
A2
AN-1
.
.
.
.
N- Inputs M- Outputs
Only one output is High for
each input
.
.
.
.
B0
B1
B2
BM-1
Fig. 1
2 to 4 Line Decoder:
➢ Block diagram of 2 to 4 decoder is shown in fig. 2
➢ Aand B are the inputs. ( No. of inputs =2)
➢ No. of possible input combinations: 22=4
➢ No. of Outputs : 22=4, they are indicated by D0, D1, D2 and D3
➢ From the Truth Table it is clear that each output is “1” for only
specific combination of inputs.
A
4
B
0
D
D1
D2
3
2 X 4
Decoder
INPUTS OUTPUTS
A B 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
Fig. 2
TRUTH TABLE
Inputs
D
Outputs
BOOLEAN EXPRESSION:
From Truth Table
D0 =A B
D2 =A B
LOGIC DIAGRAM:
D1 = A B
D3 = AB
A
A B
B
D0 =AB
D1 = A B
D2 = A B
D3 =A B
5
Fig. 3
3 to 8 Line Decoder:
➢ Block diagram of 3 to 8 decoder is shown in fig. 4
➢ A, B and C are the inputs. ( No. of inputs =3)
➢ No. of possible input combinations: 23=8
➢ No. of Outputs : 23=8, they are indicated by D0 to D7
➢ From the Truth Table it is clear that each output is “1” for only
specific combination of inputs.
3 X 8
Decoder
A
B
C
6
. D0
.
.
.
D7
Outputs
Fig. 4
Inputs
TRUTH TABLE FOR 3 X 8 DECODER:
INPUTS OUTPUTS
A B C D0 D1 D2 D3 D4 D5 D6 D7
0 0 0 1 0 0 0 0 0 0 0 D0 = A BC
0 0 1 0 1 0 0 0 0 0 0 D1 = A BC
0 1 0 0 0 1 0 0 0 0 0 D2 = A BC
0 1 1 0 0 0 1 0 0 0 0 D3 = A BC
1 0 0 0 0 0 0 1 0 0 0 D4 = A BC
1 0 1 0 0 0 0 0 1 0 0 D5 = A BC
1 1 0 0 0 0 0 0 0 1 0 D6 = A BC
1 1 1 0 0 0 0 0 0 0 1 D7 = A BC
7
LOGIC DIAGRAM OF 3 X 8 DECODER:
D0 = A B C
D1 = A B C
D2 =A B C
D3 =A B C
D4 = A B C
D5 = A B C
D6 = A B C
D7 = A B C
A B C
OUTPUTS
INPUTS
A B C
8
Fig. 5
ENCODER
• An Encoder is a combinational logic circuit.
• It performs the inverse operation of Decoder.
• The opposite process of decoding is known as Encoding.
• An Encoder converts an active input signal into a coded output signal.
• Block diagram of Encoder is shown in Fig.10. It has ‘M’inputs and ‘N’outputs.
• An Encoder has ‘M’input lines, only one of which is activated at a given time,
and produces an N-bit output code, depending on which input is activated.
-
-
-
-
-
-
-
-
-
-
-
-
-
-
‘M’
Inputs
‘N’
Outputs
Encoder
11
A0
A1
A2
AM-1
B0
B1
B2
BN-1
Fig. 10
12
• Encoders are used to translate the rotary or linear motion into a digital
signal.
• The difference between Decoder and Encoder is that Decoder has Binary
Code as an input while Encoder has Binary Code as an output.
• Encoder is an Electronics device that converts the analog signal to digital
signal such as BCD Code.
• Types of Encoders
i. Priority Encoder
ii. Decimal to BCD Encoder
iii. Octal to Binary Encoder
iv. Hexadecimal to Binary Encoder
ENCODER
Encoder
4 x 2
Decoder
2 x 4
A0
A1
A2
A3
Fig. 11
18
M=4
M=22
M=2N
‘M’is the input and
‘N’is the output
B0
B1
B2
B3
ENCODER
Encoder
4 x 2
A0
A1
A2
A3
Decoder
2 x 4
M=4
M=22
M=2N
‘M’is the input and
‘N’is the output
Fig. 12
19
00
01
10
11
ENCODER
Encoder
4 x 2
A0
A1
A2
A3
Decoder
2 x 4
M=4
M=22
M=2N
‘M’is the input and
‘N’is the output
Fig. 13
20
00
01
10
11
1
0
ENCODER
Encoder
4 x 2
A0
A1
A2
A3
Decoder
2 x 4
M=4
M=22
M=2N
‘M’is the input and
‘N’is the output
Fig. 14
21
00
01
10
11
1
0 10

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Encoders anaaaaaaaaaaaaaaad decoders.pdf

  • 2. 2 DECODER • Adecoder is a combinational circuit. • A decoder accepts a set of inputs that represents a binary number and activates only that output corresponding to the input number.All other outputs remain inactive. • Fig. 1 shows the block diagram of decoder with ‘N’ inputs and ‘M’outputs. • There are N possible input combinations and 2N output combinations. • For each of these input combinations, only one output will be HIGH (active) all other outputs are LOW • Some decoder have one or more ENABLE (E) inputs that are used to control the operation of decoder.
  • 3. BLOCK DIAGRAM OF DECODER DECODER 3 A0 A1 A2 AN-1 . . . . N- Inputs M- Outputs Only one output is High for each input . . . . B0 B1 B2 BM-1 Fig. 1
  • 4. 2 to 4 Line Decoder: ➢ Block diagram of 2 to 4 decoder is shown in fig. 2 ➢ Aand B are the inputs. ( No. of inputs =2) ➢ No. of possible input combinations: 22=4 ➢ No. of Outputs : 22=4, they are indicated by D0, D1, D2 and D3 ➢ From the Truth Table it is clear that each output is “1” for only specific combination of inputs. A 4 B 0 D D1 D2 3 2 X 4 Decoder INPUTS OUTPUTS A B 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 Fig. 2 TRUTH TABLE Inputs D Outputs
  • 5. BOOLEAN EXPRESSION: From Truth Table D0 =A B D2 =A B LOGIC DIAGRAM: D1 = A B D3 = AB A A B B D0 =AB D1 = A B D2 = A B D3 =A B 5 Fig. 3
  • 6. 3 to 8 Line Decoder: ➢ Block diagram of 3 to 8 decoder is shown in fig. 4 ➢ A, B and C are the inputs. ( No. of inputs =3) ➢ No. of possible input combinations: 23=8 ➢ No. of Outputs : 23=8, they are indicated by D0 to D7 ➢ From the Truth Table it is clear that each output is “1” for only specific combination of inputs. 3 X 8 Decoder A B C 6 . D0 . . . D7 Outputs Fig. 4 Inputs
  • 7. TRUTH TABLE FOR 3 X 8 DECODER: INPUTS OUTPUTS A B C D0 D1 D2 D3 D4 D5 D6 D7 0 0 0 1 0 0 0 0 0 0 0 D0 = A BC 0 0 1 0 1 0 0 0 0 0 0 D1 = A BC 0 1 0 0 0 1 0 0 0 0 0 D2 = A BC 0 1 1 0 0 0 1 0 0 0 0 D3 = A BC 1 0 0 0 0 0 0 1 0 0 0 D4 = A BC 1 0 1 0 0 0 0 0 1 0 0 D5 = A BC 1 1 0 0 0 0 0 0 0 1 0 D6 = A BC 1 1 1 0 0 0 0 0 0 0 1 D7 = A BC 7
  • 8. LOGIC DIAGRAM OF 3 X 8 DECODER: D0 = A B C D1 = A B C D2 =A B C D3 =A B C D4 = A B C D5 = A B C D6 = A B C D7 = A B C A B C OUTPUTS INPUTS A B C 8 Fig. 5
  • 9. ENCODER • An Encoder is a combinational logic circuit. • It performs the inverse operation of Decoder. • The opposite process of decoding is known as Encoding. • An Encoder converts an active input signal into a coded output signal. • Block diagram of Encoder is shown in Fig.10. It has ‘M’inputs and ‘N’outputs. • An Encoder has ‘M’input lines, only one of which is activated at a given time, and produces an N-bit output code, depending on which input is activated. - - - - - - - - - - - - - - ‘M’ Inputs ‘N’ Outputs Encoder 11 A0 A1 A2 AM-1 B0 B1 B2 BN-1 Fig. 10
  • 10. 12 • Encoders are used to translate the rotary or linear motion into a digital signal. • The difference between Decoder and Encoder is that Decoder has Binary Code as an input while Encoder has Binary Code as an output. • Encoder is an Electronics device that converts the analog signal to digital signal such as BCD Code. • Types of Encoders i. Priority Encoder ii. Decimal to BCD Encoder iii. Octal to Binary Encoder iv. Hexadecimal to Binary Encoder
  • 11. ENCODER Encoder 4 x 2 Decoder 2 x 4 A0 A1 A2 A3 Fig. 11 18 M=4 M=22 M=2N ‘M’is the input and ‘N’is the output B0 B1 B2 B3
  • 12. ENCODER Encoder 4 x 2 A0 A1 A2 A3 Decoder 2 x 4 M=4 M=22 M=2N ‘M’is the input and ‘N’is the output Fig. 12 19 00 01 10 11
  • 13. ENCODER Encoder 4 x 2 A0 A1 A2 A3 Decoder 2 x 4 M=4 M=22 M=2N ‘M’is the input and ‘N’is the output Fig. 13 20 00 01 10 11 1 0
  • 14. ENCODER Encoder 4 x 2 A0 A1 A2 A3 Decoder 2 x 4 M=4 M=22 M=2N ‘M’is the input and ‘N’is the output Fig. 14 21 00 01 10 11 1 0 10