In digital design, which type of programmable logic device (PLD) is most appropriate for implementing basic combinational logic functions and simple glue logic in small-scale designs?

Introduction / Context:
Programmable logic devices (PLDs) allow designers to implement custom logic without fabricating ASICs. Among the PLD family, some devices are best suited to small, basic logic tasks, while others target larger, system-level functions. This question tests recognition of which device class is typically chosen for simple combinational logic or glue logic.

Given Data / Assumptions:

• Goal: implement basic logic functions (AND/OR combinations, simple decoders, small state decoding).
• Device options span PLA, PAL, CPLD, SLD, and FPGA.
• Emphasis on simplicity, low resource count, and quick turnaround.

Concept / Approach:
PALs feature a programmable AND plane feeding a fixed OR plane. This structure is sufficient for many small-scale logic functions, is easy to program, and historically replaced multiple TTL packages in glue-logic roles. PLAs provide more flexibility (both AND and OR planes programmable) but were often used when additional product-term flexibility was needed. CPLDs and FPGAs scale to much larger systems and are overkill for very small tasks.

Step-by-Step Solution:
1) Identify the design scope: basic combinational logic.2) Map device capability to need: PAL offers simple, efficient implementation with minimal overhead.3) Compare alternatives: PLA is more flexible but not necessary for most simple tasks; CPLD/FPGA are larger and more complex.4) Conclude: PAL is the most appropriate choice.

Verification / Alternative check:
Typical legacy designs replaced several 74xx TTL gates with a single PAL. If additional flexibility or density was required, designers moved up to a PLA or CPLD.

Why Other Options Are Wrong:
PLA: more flexible than necessary for basic tasks.

CPLD/FPGA: suited for larger designs; unnecessary complexity for simple glue logic.

SLD: not a standard mainstream category in this context.

Common Pitfalls:
Jumping directly to CPLD/FPGA for tiny tasks increases cost and complexity. Always match device class to problem size.

Final Answer:
PAL (Programmable Array Logic)