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## Chapter 5 Karnaugh Maps

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**Chapter 5 Karnaugh Maps**ECG 100-001 Logic Design 1 Mei Yang**Minimum Forms of Switching Functions**• When a function is realized using AND and OR gates, the cost is directly related the number of gates and gate inputs used. • Minimum SOP: A SOP form which (a) has a minimum number of terms and (b) for those expressions which have the same minimum number of terms, has a minimum number of literals. • Minimum POS: A POS form which (a) has a minimum number of terms and (b) for those expressions which have the same minimum number of terms, has a minimum number of literals.**Why Kmap?**• Problems with the simplification method using Boolean algebra • The procedures are difficult to apply in systematic way. • It is difficult to tell when you have arrived at a minimum solution. • Kmap is a systematic method, which is especially useful for simplifying functions with three or four variables.**Plotting Kmaps**• From truth tables • From minterm/maxterm expansions • From algebraic expressions • Examples on pp. 122-124**3-Variable Karnaugh Map**• Boolean adjacency -difference in one variable • Grouping adjacent 1’s**Grouping Principle**• Groupings can contain only 1s; no 0s. • Groups can be formed only at right angles; diagonal groups are not allowed. • The number of 1s in a group must be a power of 2 – even if it contains a single 1. • The groups must be made as large as possible. • Groups can overlap and wrap around the sides of the Kmap. • Use the fewest number of groups possible.**3-Variable Karnaugh Map**Grouping of adjacent 1’s • Multiple grouping**3-Variable Karnaugh Map**• Corresponding minterms • Adjacent minterms**A Systematic Way for Minimization**• Any single one or any group of ‘1’ s is called an IMPLICANT of F. • A group (covering) that cannot be combined with some other 1’s or coverings to eliminate a variable is called PRIME IMPLICANT.**Minimization with Don’t Cares**• Threat X’s as 1’s if you will get a larger grouping. Otherwise, treat them as 0’s.**Obtaining Minimum POS Equation**• Grouping 0’s means obtaining a minimum SOP for F’.**Minimization Rules**• The minimum SOP expression consists of some (but not necessarily all) of the prime implicants of a function. • If a SOP expression contains a term which is NOT a prime implicant, then it CANNOT be minimum.**Minimization Rules**• How to use prime implicants for obtaining a minimum SOP equation?**Essential Prime Implicants**F(A,B,C,D)= BC’ +A’B’D BC’ and A’B’D are called the Essential Prime Implicants, because they cover ‘1’s that cannot be covered by any other coverings. A’CD is not an essential, and it is not included, because all 1’s are already covered, and there is no reason to add an extra term.**Minimum SOP**• To obtain a minimum SOP equation • Include all essential prime implicants to the equation. • Check if all ones are covered by the essential prime implicants. • If there are remaining ‘1’s, include non-essential prime implicants. • There can be more than one minimum SOP equation equally valid.**Example 2: F = ∑m (0,1,2,4,5,8,9,10,17,18,19,25,26)**Essential prime implicants are shown in sold line groups and other prime implicants are shown in dotted line groups. F = A'B'D'+C’D'E+C'DE’+ {AB’C’E or AB’C’D}+{A’BC’D’ or A’BC’E’}