Programmable Logic Devices
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Figure 9.14 Solution to problem 9.2 using a PROM.
Example 9.3
We have two two-bit binary numbers A 1 A 0 and B 1 B 0 . Design a PLA device to implement a magnitude
comparator to produce outputs for A 1 A 0 being ‘equal to’, ‘not equal to’, ‘less than’ and ‘greater than’
B 1 B 0
Solution
Table 9.2 shows the function table with inputs and desired outputs. The Boolean expressions for the
desired 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)