Vendor architectures — PAL vs. PLA in classic CPLDs Which statement correctly matches the traditional internal array style associated with Altera and Xilinx CPLD families?

Introduction / Context:
Classic CPLDs from major vendors historically differed in their internal product-term array structures. “PAL” generally denotes a programmable AND array feeding a fixed OR array, while “PLA” denotes both AND and OR arrays being programmable. Recognizing these differences helps interpret how equations map to silicon resources and why product-term allocation behaves differently across families.

Given Data / Assumptions:

• Altera MAX-series CPLDs historically favored PLA-like flexibility.
• Xilinx XC9500-series CPLDs are commonly described as PAL-like product-term devices.
• Both vendors also offer FPGA families that use LUTs (a different architecture).

Concept / Approach:
In a PLA-style device, both planes (AND and OR) are programmable, offering more freedom in assigning product terms to outputs. In PAL-style devices, the OR plane is more constrained (fixed), which can simplify timing at the cost of flexibility. The common textbook matching is Altera → PLA-like, Xilinx → PAL-like for their classic CPLD lines.

Step-by-Step Reasoning:

Verification / Alternative check:
Vendor application notes and many digital design textbooks describe Altera MAX devices with flexible product-term sharing (PLA-like) and Xilinx XC9500 with fixed product-term allocations per macrocell (PAL-like), which aligns with the selected answer.

Why Other Options Are Wrong:

• Swapped or “both same” statements contradict widely cited architectural descriptions.
• “LUT-only” applies to mainstream FPGAs, not to classic product-term CPLDs.

Common Pitfalls:

• Assuming all programmable logic uses LUTs; CPLDs are product-term devices.

Final Answer:
Altera uses PLA architecture and Xilinx uses PAL architecture.