SEQUENTIAL AND COMBINATIONAL CIRCUITS,DIGITAL LOGIC DESIGN

COMBINATIONAL AND SEQUENTIAL CIRCUITS,DESIGN AND ANALYSIS PROCEDURE OF COMBINATIONAL CIRCUITS,

1. DIGITAL LOGIC CIRCUITS ~ INTRODUCTION TO COMBINATIONAL AND SEQUENTIAL CIRCUITS. ~DESIGN PROCEDURE OF COMBINATIONAL CIRCUITS ~ANALYSIS PROCEDURE OF COMBINATIONAL CIRCUITS PRESENTED BY: QURATULAIN BS(CS )- 1 QUAID-E-AZAM UNIVERSITY ISLAMABAD ,PAKISTAN.

2. TYPES OF DIGITAL LOGIC CIRCUITS COMBINATIONAL CIRCUITS SEQUENTIAL CIRCUITS

3. COMBINATIONAL CIRCUITS Combinational Circuits are made of logic gates. Doesn’t contain memory element , that’s why they cant store any information. Value of present output is determined by present input. Examples of combinational circuits are half adders, full adders, sub tractors etc.

4. BLOCK DIAGRAM OF A COMBINATIONAL CIRCUIT

5. SEQUENTIAL LOGIC CIRCUITS Made up of combinational circuits and memory elements. These memory elements are devices capable of storing ONE-BIT information. Output depend on input and previous state. Examples of sequential circuits are flip flops, counters, shift registers

6. BLOCK DIAGRAM OF A SEQUENTIAL CIRCUIT

7. TYPES OF SEQUENTIAL CIRCUITS Sequential circuits are of two types: 1.SYNCHRONOUS CIRCUITS: In synchronous sequential circuits, the state of the device changes only at discrete times in response to a clock Pulse. 2.ASYNCHRONOUS CIRCUITS: Asynchronous circuit is not synchronized by a clock signal; the outputs of the circuit change directly in response to changes in Inputs.

8. DESIGN PROCEDURE OF COMBINATIONAL CIRCUITS This procedure involves the following steps: The problem is stated. The number of available input variables and output variables is determined. The input and output variables are assigned letter symbols. Truth table is drawn Boolean function for output is obtained. The logic diagram is drawn.

9. ANALYSIS PROCEDURE OF COMBINATIONAL CIRCUIT TO DETERMINE THE OUTPUT FUNCTIONS AS ALGEBRAIC EXPRESSIONS. It is the reverse process of design procedure. Logic diagram of the circuit is given. Obtain the truth table from the diagram. Obtain Boolean function from the Truth Table for output.

10. LOGIC DIAGRAM FOR ANALYSIS EXAMPLE:

11. THE CIRCUIT HAS THREE INPUTS, A,B,C AND TWO OUTPUTS F1 AND F2 The Boolean function for outputs are: F2=AB+AC+BC T1=A+B+C T2=ABC Outputs functions for gates are : T3=F2’T1 F1=T3+T2

12. Substituting and simplifying, we get :

13. TRUTH TABLE DRAWN FROM THE LOGIC DIAGRAM.

14. BOOLEAN FUNCTIONS OBTAINED FOR OUTPUT ARE : F2=AB+AC+BC F1=A’BC’+A’B’C+AB’C’+ABC