1. Chapter 3 Digital Logic Structures

2. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-2 Complete Example A blinking traffic sign No lights on 1 & 2 on 1, 2, 3, & 4 on 1, 2, 3, 4, & 5 on (repeat as long as switch is turned on) DANGER MOVE RIGHT 1 2 3 4 5

3. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-3 Traffic Sign State Diagram State bit S 1 State bit S 0 Switch on Switch off Outputs Transition on each clock cycle.

4. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-4 Traffic Sign Truth Tables Outputs (depend only on state: S 1 S 0 ) S1S1 S0S0 ZYX 00000 01100 10110 11111 Lights 1 and 2 Lights 3 and 4 Light 5 Next State: S 1 ’S 0 ’ (depend on state and input) InS1S1 S0S0 S1’S1’S0’S0’ 0XX00 10001 10110 11011 11100 Switch Whenever In=0, next state is 00.

5. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-5 Traffic Sign Logic Master-slave flipflop

6. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Controller + Data Path Sometimes there are lots and lots of states, but a fairly simple way to move between states. We can separate the data being transformed from the state machine that's controlling the transform. 3-6 State Machine Combinational Logic Circuit Storage Elements Controller+Data Path

7. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Controller + Data Path Example (1) 3-7

8. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Controller + Data Path Example (2) 3-8

9. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-9 From Logic to Computer Data Path The data path of a computer is all the logic used to process information. See the data path of the LC-3 on next slide. Combinational Logic Decoders -- convert instructions into control signals, access memory Multiplexers – select inputs and outputs ALU (Arithmetic and Logic Unit) – performs operations on data Sequential Logic State machine -- coordinate control signals and data movement Registers and latches -- storage elements

10. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-10 LC-3 Data Path