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Therearetwotypesoflogiccircuits 1combinationallogic

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Unformatted text preview: eck. 4 10/13/2011 Example 13 • Perform binary subtraction: 3 ‐10 Note: smaller no – greater no (check lecture notes) • Perform binary subtraction: 10 – 3 • Perform binary subtraction: 25 – 8 01100 ‐ 10101 0 1 0 1 0 1 inverting 1 0 1 0 1 0 + 1 1 0 1 0 1 1 + 0 0 1 1 0 0 1 1 0 1 1 1 ‐1 1 1 0 1 1 0 Check: (01100)2 = 1 x 22+ 1 x 23 = 4 + 8 = (12)10 (10101)2 = 1 x 20 + 1 x 22+ 1 x 24 = 1 + 4 + 16 = (21)10 (01001)2 = 1 x 20+ 1 x 23 = 1 + 8 = (9)10 12 ‐ 21 = ‐9 inverting 0 0 1 0 0 1 5 10/13/2011 Logic circuits Combinational / sequential • Digital logic can be implemented in circuits called digital logic circuits. • There are two types of logic circuits. • (1) combinational logic • (2) Sequential logic • These are used in computers and form part of ARTHIMETIC LOGIC UNIT • Combinational – output is a pure function of present input – no memory • Sequential – Output depends not only on the present input but also on the history of the input – memory Assigning logic variables Truth tables • Assign logic variable to precise statement • Example: David’s purchase • Exhaustive description of output for all possible inputs • Example – Phone rings (R=1) if power on (P=1) and incoming call (C=1) 2N combinations for N inputs – He buys if he wants an item and has cash or if he needs it and has cash or card – David needs item (N=1) – David wants item (W=1) – David has sufficient cash for purchase (C=1) – David has...
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This note was uploaded on 05/05/2013 for the course ELEC 1111 taught by Professor Jayashriravishankar during the One '11 term at University of New South Wales.

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