4.3.10

Adder Circuits

Test yourself

Adder Circuits

Adder circuits are used by the Arithmetic Logic Unit (ALU) in a processor to perform the addition of two binary digits.

Illustrative background for Types of adder circuitIllustrative background for Types of adder circuit ?? "content

Types of adder circuit

  • Adder circuits come in two forms:
    • Half adder circuits.
    • Full adder circuits.
Illustrative background for Half adder circuitsIllustrative background for Half adder circuits ?? "content

Half adder circuits

  • Half adder circuits accept two inputs and output both the result and a carry bit.
  • They make use of an XOR gate and an AND gate, laid out as shown.
Illustrative background for Half adder tableIllustrative background for Half adder table ?? "content

Half adder table

  • The actions of the two gates can be displayed in a table as shown.
  • The output at S gives the 20 binary digit.
  • The output at C gives the 21 binary digit (the carry bit).
Illustrative background for Full adder circuitsIllustrative background for Full adder circuits ?? "content

Full adder circuits

  • Full adders have the same output as a Half Adder (the sum and a carry bit), but they accept three inputs (two bits plus a carry bit).
  • They are constructed from two Half Adders.
Illustrative background for Full adder tableIllustrative background for Full adder table ?? "content

Full adder table

  • In a full adder:
    • S = A XOR B XOR C(in)
    • C(out) = (A AND B) OR (C(in) AND (A XOR B))

Jump to other topics

1Components of a Computer

2Software & Software Development

3Exchanging Data

4Data Types, Data Structures & Algorithms

5Legal, Moral, Cultural & Ethical Issues

6Elements of Computational Thinking

6.1Thinking Abstractly

6.2Thinking Ahead

6.3Thinking Procedurally

6.4Thinking Logically

6.5Thinking Concurrently

7Problem Solving & Programming

8Algorithms

Unlock your full potential with Seneca Premium

  • Unlimited access to 10,000+ open-ended exam questions

  • Mini-mock exams based on your study history

  • Unlock 800+ premium courses & e-books

Get started with Seneca Premium