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Combinationalcircuits
This document provides an overview of combinational logic circuits such as adders, subtractors, and multiplexers. It describes half adders and full adders that perform binary addition of two and three bits respectively. Binary adders can be constructed by cascading full adders. Binary subtractors use half and full subtractors to perform subtraction by taking the 2's complement of one number and adding it to the other. An example circuit is shown that can function as either an adder or subtractor based on a mode input. Finally, multiplexers are described as circuits that select one of several input lines to output based on selection lines.
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Combinationalcircuits
- 1. 1 Combinational logic circuits AmjadHassan Khan MK Lecturer in Electronics Kristu Jayanti College, Bangalore
- 2. 2 overview What iscombinational logic circuit ? Examples of combinational logic circuits Binary-adder Binary-subtractor Multiplexers
- 3. 3 Combinational logic circuit Combinational circuits consists of logic gates whose outputs depends on the present inputs .They have no memory element . It consists of input variables , logic gates & output variables .
- 4. 4 Binary-Adder Half-Adder : A combinational circuit that performs the addition of two bits at a time is called “ Full-Adder ‘’ . The input variables designate the augend and addend bits ; the output variables produce the sum & carry .
- 5. 5 Circuit & truthtableof Half-Adder Circuit diagram Truthtable
- 6. 6 Full-Adder : Acombinational circuit that performs the addition of three bits at a time is called “ Full-Adder ’’ Block diagram & the truth table of Full- Adder .
- 7. 7 Circuit diagrams offull-adder
- 8. 8 Binary-Adder A Binary-Adderis a digital circuit that produces the arthimatic sum of two binary numbers at a time . It can also construct by cascading no of full-adders we get a N-bit binary- adder circuit . An N-bit adder requires n full-adders with each output carry connected to the input carry to the next full-adder .
- 9. 9 For adding 4-bitbinary numbers we need four full-adders as shown below :
- 10. 10 Binary-subtractor Half-subtractor : A combinational circuit which performs the subtraction of two bits at a time is called “ Half-subtractor “ . It has two inputs & two outputs . The two inputs x & y form the minuend & subtrahend & D is the difference output & B is the borrow output .
- 11. 11 Circuit & truthtableof half- subtractor circuit diagram Truthtable
- 12. 12 Full subtractor Acombinational circuit which performs the subtraction of three bits at a time is called “ Full subtractor “ . A full subtractor has three inputs x y Bin & two outputs D & Bout .
- 13. 13 Circuit & truthtableof full subtractor circuit diagram Truthtable
- 14. 14 Binary-subtractor The subtractioncan be done by taking the 2’s compliment of B and adding it to A . 2’s compliment can be obtained by taking the 1’s compliment and adding 1 to least significant bit . 1’s compliment can be obtained by changing 1’s into 0’s & 0’s into 1’s .
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- 16. 16 Continues….. In thiscircuit the mode input m controls the operation . When m=0 , the circuit is an adder circuit . When m=1, the circuit becomes a subtractor . The c & v are two outputs . C is for carry & v is for overflow . If v=0 after an addition or subtraction ,then no overflow occurred and the n-bit result is correct . If v=1 , then the result of the operation contains n+1 bits .
- 17. 17 Multiplexer multiplexer isa combinational circuit that selects binary information from one of many input lines and directs it to a single output line . Normally there are 2n input lines and n selection lines whose bit combinations determines which input is selected . A multiplexer is also called ‘ Data selector ’
- 18. 18 Four - to- one line multiplexer circuit & truth table :
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