1. CO UNIT-I

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

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

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

6. 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

7. Demultiplexer Takes one input Out to one of 2 n possible outputs 1-to-4-Line Demultiplexer

8. 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

9. Truth Table: 8-to-3 Binary Encoder

10. Decoders Typically n inputs and 2 n outputs The output line corresponding to the input code is high 1-to-2 Line Decoder

11. 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 1 0 0 1 1 A 0 0 1 0 1 D 0 1 0 0 0 D 1 0 1 0 0 D 2 0 0 1 0 D 3 0 0 0 1 (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 = = = =

12. 2-to-4 Decoder with Enable

13. 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