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Digital logic

1. Faculty Of Engineering and Technology Department of Computer Science Course: Digital Logic and Design-I Course Code : CS-105 (4) ( Lecture-11) Sayed Mortaza Kazemi Department of Computer Science Email : [email protected] Mobile: [phone]

2. Adders

3. OUTCOMES At the end of this lecture, students will know; Designing of Half and Full Adder circuits. 3

4. Adder The logic Gates which form the basic building blocks of a digital system are designed to perform simple logic operations. A single logic gate is not of much use unless it is connected with other gates to collectively act upon data. Different gates are combined to build a circuit that is capable of performing some useful operation like adding three numbers.

5. Combinational Logic Circuit Such circuits are known as combinational Logic Circuits. An Adder combinational Circuit that is to add single bit binary numbers and give a single bit Sum and Carry output . The output of the single bit adder circuit generates a sum bit and a carry bit. A single digit binary adder circuit therefore has three inputs, one A input , B input and third represent the carry .

6. Half Adder and Full Adder The single bit binary adder has two bit output. One bit represents the sum and the other represent Carry bit. There are two types of Adder . Half Adder Full Adder

7. Half Adder A n adder that only has two bit input representing the two single bit numbers A and B and does not have the carry bit input from the least significant digit is regarded as a half-adder.

8. Half Adder To design a combinational circuit first, the inputs and outputs should be identified. then Function Table/Truth table Expression Logic Circuit.

9. Half Adder Function Table The Half-Adder has 2-bit input and a 2-bit output. The function table of the Half-Adder has two input columns representing the two single bit numbers A and B. The function table also has two output columns representing the Sum bit and Carry Out bit. Input Output A B Sum Carry Out 1 1 1 1 1 1 1

10. Half Adder Curcuit .

11. Full Adder An adder circuit that has three inputs, two bits representing the two single bit numbers A and B, and the third bit represents the Carry in bit is regarded as a full-adder A full – Adder can be fully described in term of its function table, its Sum and Carry Out .

12. Full Adder Function Table The Full – adder has a 3-bit input and a 2-bit output. The function table of the Full – adder has three input columns representing the two single bit number A, B and the carry In bit. The function table also has two output columns representing the Sum bit Carry bit and Carry Out bit.

13. Full Adder Function Table . Input Output A B Carry In (C) Sum Carry Out 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

14. Full Adder Circuit Full-Adder = Half-Adder + Half-Adder

15. Thank You…!