Page 143 - DCAP108_DIGITAL_CIRCUITS_AND_LOGIC_DESIGNS

Digital Circuits and Logic Design

Notes Implement the following function by ROM and PLA:

f(A, B, C) = Σ(0, 2, 4, 5, 7)
This function is implemented by ROM as the OR of five minterms:
f(A, B, C) = A’B’C’ + A’BC’ + AB’C’ + AB’C + ABC
Figure 8.11: PLA implementation (a) Rom Implementation (b) K-Map for Simplification
(c) Logic Implementation of PLA (d) Circuit Diagram

(a)
But after simplification by Karnaugh map:

(b)

The function can be implemented by a PLA as the OR of three terms:
f(A, B, C) = AC + A’C’ + AB’

(c)

Note that in a PLA, only those terms that are needed are generated by the AND array, while
in a ROM, all minterms have to be generated by the AND array.

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