Difficulty: Easy
Correct Answer: The PLA has a programmable OR plane and a programmable AND plane, while the PAL only has a programmable AND plane
Explanation:
Introduction / Context:
PLAs and PALs are foundational PLDs that realize sum-of-products logic. Their capabilities depend on whether the AND and OR planes are fixed or programmable. Recognizing which planes are programmable determines flexibility and resource usage in logic synthesis.
Given Data / Assumptions:
Concept / Approach:
A PLA exposes programmability in both the AND plane and the OR plane, providing maximum flexibility to create any required product terms and sums. A PAL typically provides a programmable AND plane feeding a fixed OR plane, simplifying hardware and programming at the cost of flexibility. This distinction is standard and appears across classic device families.
Step-by-Step Solution:
1) Define planes: AND plane creates product terms; OR plane sums those terms.2) PLA: AND programmable + OR programmable → high flexibility.3) PAL: AND programmable + OR fixed → simpler, less flexible.4) Therefore, option (a) correctly states the difference.
Verification / Alternative check:
Historical datasheets and textbooks consistently describe PLAs with both planes programmable and PALs with only the AND plane programmable.
Why Other Options Are Wrong:
Option (b) reverses the roles and is incorrect.
Option (c) is not inherently true across all devices; capacity varies by part number.
Option (d) is false; they are distinct.
Option (e) is incorrect; both support combinational logic, and sequential features (like registers) are device-dependent add-ons.
Common Pitfalls:
Assuming all PALs can realize any sum-of-products like PLAs; OR-plane fixity can constrain mapping and require re-expression of logic.
Final Answer:
The PLA has a programmable OR plane and a programmable AND plane, while the PAL only has a programmable AND plane
Discussion & Comments