CO UNIT-I. 2 Multiplexers: A multiplexer selects information from an input line and directs the...
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Transcript of CO UNIT-I. 2 Multiplexers: A multiplexer selects information from an input line and directs the...
CO
UNIT-I
2
Multiplexers:• A multiplexer selects information from an input
line and directs the information to an output line
• A typical multiplexer has– n selection control inputs (Sn - 1, … S0)
– 2n information data inputs (I2n
- 1, … I0)– one output Y
3
Multiplexers (continued)• A multiplexer can be designed to have
– n selection inputs– m information inputs with m < 2n
Design of a 2/1 Mux
• 2/1 mux Block Diagram• Truth Table
D1
D0
S
OS D1 D0 O
0 0 0 0
0 0 1 1
0 1 0 0
0 1 1 1
1 0 0 0
1 0 1 0
1 1 0 1
1 1 1 1
A Single Bit 4-to-1 Line Multiplexer
4-to-1-Line Multiplexer
I0
I1
I2
I3
I0
I1
I2
I3
Uses of Multiplexers
– Used in data communications for several computers to communicate over 1 line
– Used in radio to select one channel from many– Used to route data within a computer– Used for function generation
Demultiplexer
• Takes one input• Out to one of 2n possible outputs
1-to-4-Line Demultiplexer
Encoder
• Encoder is the opposite of decoder• 2n inputs
– or less – 10 inputs in “Decimal to BCD” encoder: I0, I1, I2, I3, …, I9
• n outputs– 4 output lines “Decimal to BCD”encoder
Truth Table: 8-to-3 Binary Encoder
Decoders
• Typically n inputs and 2n outputs • The output line corresponding to the input
code is high
1-to-2 Line Decoder
11
• 2-to-4-Line Decoder
Note that the 2-4-line made up of 2 1-to-2- line decoders and 4 AND gates.
Decoder Examples
A1
0
0
1
1
A0
0
1
0
1
D0
1
0
0
0
D1
0
1
0
0
D2
0
0
1
0
D3
0
0
0
1
(a)
D0 A1 A0
D1 A1 A0
D2 A1 A0
D3 A1 A0
(b)
A1
A0
=
=
=
=
2-to-4 Decoder with Enable
Uses for Decoders
• Binary number might serve to select some operation– Computer operation codes are encoded
• Decoder lines might select add operation, or subtract operation, or multiply operation, etc.
• Memory address lines