## PHYS345 Electricity and Electronics

Truth Table Set-Ups for Karnaugh Mapping

Each truth table consists of 2n cells, where n is the number of inputs (logic variables).

Two Inputs (4 cells)

B 0  1
A\
0     __   __
1     __   __

The row and column assignments for two or more variables are arranged so that adjacent terms change by only one bit. That is, the possibilities of AB are considered as 00, 01, 11, and 10 in turn, rather than 00, 01, 10, and 11 as often is written sequence in ordinary truth tables. (In going from 01 to 10, both bits would be changed.) This type of construction facilitates identification of supercells that are used to simplify gate combinations for realizing the desired truth table.

Three Inputs (8 cells)

C 0  1
AB\
00     __   __
01     __   __
11     __   __
10     __   __
OR
BC 00  01  11  10
A\
0     __   __   __   __
1     __   __   __   __

Four Inputs (16 cells)

CD 00  01  11  10
AB\
00     __   __   __   __
01     __   __   __   __
11     __   __   __   __
10     __   __   __   __