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Logic Gates

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Logic Gates

  1. 1. Logic Gates 1
  2. 2. • Saqib Naveed sendsaqib@gmail.com 03345813561 2
  3. 3. •What is Logic?? 3
  4. 4. 4
  5. 5. 5 Logic Reasoning conducted or assessed according to strict principles of validity. a system or set of principles underlying the arrangements of elements in a computer or electronic device so as to perform a specified task.
  6. 6. Logic Gates. Logic gates are electronic circuits that operate on one or more input signals to produce an OUtput signal.
  7. 7. Boolean algebra is the algebra of two values. These are usually taken to be 0 and 1, as we shall do here, although F and T, false and true, etc. are also in common use.
  8. 8. Basic logic gates • Not • And • Or • Nand • Nor • Xor 8
  9. 9. Truth Table A truth table is a mathematical table used in logic— specifically in connection with Boolean algebra, boolean functions, and propositional calculus—to compute the functional values of logical expressions on each of their functional arguments, that is, on each combination of values taken by their logical variables ...
  10. 10. A a A 0 1 1 0 Truth Table: A The output A is true when the input a is NOT true, the output is the inverse of the input: a = NOT A A NOT gate can only have one input. A NOT gate is also called an inverter. NOT
  11. 11. AND A B A*B Logic Gate: Series Circuit: A B AA BB A*BA*B 00 00 00 00 11 00 11 00 00 11 11 11 Truth Table:A*B "If A AND B are both 1, then Q should be 1.“ (All or nothing.)
  12. 12. Three Input AND Gate A B C ABC 0 0 0 0 0 0 1 0 0 1 0 0 0 1 1 0 1 0 0 0 1 0 1 0 1 1 0 0 1 1 1 1
  13. 13. A B A+B Logic Gate: Parallel Circuit: A B AA BB A+BA+B 00 00 00 00 11 11 11 00 11 11 11 11 Truth Table:A+B OR "If A is 1 OR B is 1 (or both are 1), then Q is 1."
  14. 14. • Find the output of the following circuit • Answer: (x+y)y 14 x+y y (x+y)y ____
  15. 15. • Because + and * are binary operations, they can be cascaded together to OR or AND multiple inputs. A B C A B C A+B+C A+B+C A B A B C ABC ABC
  16. 16. NAND and NOR Gates • NAND and NOR gates can greatly simplify circuit diagrams. NAND inverts the output of AND. • NOR inverts the output of OR. NAND NOR AA BB AA↑↑BB 00 00 11 00 11 11 11 00 11 11 11 00 AA BB AA↓↓BB 00 00 11 00 11 00 11 00 00 11 11 00
  17. 17. XOR and XNOR Gates XOR XNOR AA BB AA⊕⊕BB 00 00 00 00 11 11 11 00 11 11 11 00 A B A B 0 0 1 0 1 0 1 0 0 1 1 1 XOR (exclusive OR) :"If either A OR B is 1, but NOT both, Q is 1." XNOR (exclusive NOR) : invert output of XOR
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