Wednesday, 29 February 2012

PAL


Programmable array logic consists of programmable AND array and fixed OR array.
In PROM all 2n minterms are generated in AND array by using decoder. But in PAL only limited numbers of min terms are generated. So designers must use them efficiently.
Cost of PAL is less than PROM and PLA.
A min term in PAL can’t be shared between two functions that are going to be implemented on the same PAL. Below figure shows the PAL diagram.

Implementation of Boolean function:
Implement f1 (A, B, C, D) = ∑ (5, 6, 7, 8, 10)
f2 (A, B, C, D) = ∑ (0, 2, 3, 6, 9, 11, 13)
f3 (A, B, C, D) = ∑ (1, 4, 5, 7, 8, 10, 15) with 4-wide AND-OR structured PAL.
f1=A’BD+A’BC+AB’D’
f2=A’B’D’+B’CD+AC’D+A’CD’
f3=A’BC’+BCD+A’C’D+AB’D’
 
AB’D’ is common in both f1 and f3 but I can’t be shared between the functions in PAL implementation

PAL table:
Implementation:
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