Programmable-logic expanders in SOP architectures: Evaluate the statement — “Expanders make it possible to increase the number of product terms available to a programmable sum-of-products (SOP) operation.”

Introduction / Context:Many PLDs and CPLDs implement logic as sum-of-products fed into macrocell OR arrays. Complex functions may exceed the native product-term budget per output. Vendors therefore provide “expanders” or product-term sharing mechanisms that add more terms to a macrocell’s OR stage without external logic.

Given Data / Assumptions:

• Target architecture: programmable SOP with limited product terms per macrocell.
• Expanders or product-term allocators are available within the device.
• Goal: realize wider logic expressions than a single macrocell allows.

Concept / Approach:Expanders route additional product terms from neighboring macrocells or from a shared pool into a target macrocell’s OR function. This increases functional capacity while staying on-chip, reducing pin usage and delay compared to external “glue” logic.

Step-by-Step Solution:

Verification / Alternative check:Compile the design both with and without expanders. Without expanders, the fitter may fail or spill logic externally. With expanders, the fitter reports extra product terms borrowed and a successful fit.

Why Other Options Are Wrong:

• Incorrect: Expanders do increase available product terms.
• True only for ROM-based PLDs: Product-term expanders are typical of PLA/CPLD-style devices, not restricted to ROM arrays.
• True only when outputs are registered: Registration is orthogonal to product-term availability.
• Depends on external glue logic: Expanders reduce the need for external glue.

Common Pitfalls:Overusing expanders and creating routing congestion; ignoring timing when pulling terms from distant macrocells; assuming expanders are unlimited.

Final Answer:Correct