Digital Electronics: Principles, Devices and Applications

Programmable Logic Devices 315ABCiSCoFigure 9.14Solution to problem 9.2 using a PROM.Example 9.3We have two two-bit binary numbers A 1 A 0 and B 1 B 0 . Design a PLA device to implement a magnitudecomparator to produce outputs for A 1 A 0 being ‘equal to’, ‘not equal to’, ‘less than’ and ‘greater than’B 1 B 0 SolutionTable 9.2 shows the function table with inputs and desired outputs. The Boolean expressions for thedesired outputs are given in the following equations:Output 1equal to = A 1 A 0 B 1 B 0 + A 1 A 0 B 1 B 0 + A 1 A 0 B 1 B 0 + A 1 A 0 B 1 B 0 (9.5)Output 2 (not equal to)= A 1 A 0 B 1 B 0 + A 1 A 0 B 1 B 0 + A 1 A 0 B 1 B 0 + A 1 A 0 B 1 B 0 + A 1 A 0 B 1 B 0 + A 1 A 0 B 1 B 0 + A 1 A 0 B 1 B 0+ A 1 A 0 B 1 B 0 + A 1 A 0 B 1 B 0 + A 1 A 0 B 1 B 0 + A 1 A 0 B 1 B 0 + A 1 A 0 B 1 B 0 (9.6)