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 (S n  1, … S 0 ) – 2 n information data inputs (I 2 n  1, … I 0 ) – one output Y

3 Multiplexers (continued) A multiplexer can be designed to have – n selection inputs – m information inputs with m  2 n

Design of a 2/1 Mux 2/1 mux Block Diagram Truth Table D1D1 D0D0 S O S D 1 D 0 O

A Single Bit 4-to-1 Line Multiplexer 4-to-1-Line Multiplexer I0I0 I1I1 I2I2 I3I3 I0I1I2I3I0I1I2I3

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 2 n possible outputs 1-to-4-Line Demultiplexer

Encoder Encoder is the opposite of decoder 2 n inputs – or less – 10 inputs in “Decimal to BCD” encoder: I 0, I 1, I 2, I 3, …, I 9 n outputs – 4 output lines “Decimal to BCD”encoder

Truth Table: 8-to-3 Binary Encoder

Decoders Typically n inputs and 2 n 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 A A D D D D (a) D 0 A 1 A 0 D 1 A 1 A 0 D 2 A 1 A 0 D 3 A 1 A 0 (b) A 1 A 0 = = = =

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