Quine-McCluskey (Tabulation) Method

Quine-McCluskey (Tabulation) Method is an alternative method to replace Karnaugh-Map(K-maps). When there are more than 6 variables ,K-maps are not efficient to minimized standard from Boolean function. However, for functions with more than six variables, it becomes very difficult to visualize how the minterms should be combined into subcubes. In addition, the K-map algorithm is not as straight forward to program the computer with. There exist a tabulation method called Quine-McClusky method that are better suited for programming the computer, and thus can solve any function having any number of variables.

Example: f(w,x,y,z) = Σ(0,2,5,7,10,13,14,15)

The minterms is group according to the numbers of 1's in the minterms binary representation. For Example the Group₀ does not have any 1's binary(0000),the group₁ has only one 1's(0010), the group₂ got 2 subcube minterms that have two 1's.

The next step, we construct another tables by combining the minterms in adjacent groups from the first
table that differ in only one bit position. For example, m₀ and m₂ differ in only the y bit. Thus, this table lists all the1-subcubes. A hyphen (-) is used in the bit position that is different in the two minterms. Since this 1-subcube covers the two individual minterms, we make a note of it by checking the two minterms in the "Subcube Covered" column in the previous table. The 1-subcube table is shown next

1-subcube table

We repeat the second step as long as there are adjacent subcubes that differ in only one bit position including the hyphen. These subcubes are combined to give the next subcube table. From the above 1-subcube table, we get the following 2-subcube table.

2-subcube table

We stop when there are no more subcubes that can be combined. The prime implicants are those subcubes that are not covered, i.e. those without a check mark in the Subcube Covered column. For example, from the last table (2-subcube table) the only subcube in this table has the value x = 1 and z = 1, thus we get the prime implicant xz.

From the 1-subcube table, we have the four prime implicants w'x'z', x'yz', wyz', and wxy. Note that these prime implicants may not necessary be all in the last table.

F = w'x'z' + xz + wyz'