GAL16V8 device pin capabilities — identify the configurable I/O pins In the standard 20-pin GAL16V8 (Generic Array Logic) device used in digital design, which statement correctly describes its pin capabilities?

Difficulty: Easy

Correct Answer: 8 pins that are used as inputs or outputs.

Explanation:


Introduction / Context:
The GAL16V8 is a popular small programmable logic device used to implement glue logic, state machines, and decoders. Understanding its pinout and which pins are fixed versus configurable is foundational when replacing multiple SSI/MSI gates with a single PLD on a PCB.


Given Data / Assumptions:

  • Package: typically 20 pins with VCC and GND fixed.
  • One side of the device provides dedicated inputs.
  • The opposite side presents eight configurable macrocells that can function as outputs or as additional inputs, depending on the chosen mode.


Concept / Approach:
GAL16V8 devices combine a programmable AND array with macrocells that can be configured per pin. The classic allocation is eight dedicated input pins (often on the left side) and eight configurable I/O macrocells (often on the right side). Therefore, the correct characterization is that there are eight pins that can be used as inputs or outputs depending on the JEDEC configuration and design constraints.


Step-by-Step Solution:

Identify fixed resources: power pins and certain control pins are fixed-function.Count dedicated inputs: eight pins are input-only in common operating modes.Count configurable macrocells: eight pins may act as outputs (with optional registered/comb modes) or be configured as inputs.Conclude that “8 pins that are used as inputs or outputs” correctly describes the GAL16V8.


Verification / Alternative check:
Typical datasheets enumerate pins 2–9 as dedicated inputs and pins 12–19 as I/O macrocells. Mode tables (e.g., Simple, Complex, Registered) control whether a macrocell acts as a combinational or registered output or is folded back as an input to the array.


Why Other Options Are Wrong:

  • 16 dedicated inputs: contradicts the macrocell I/O capability.
  • “8 special function pins”: vague and not the standard description.
  • “All of the above”: cannot be true given (a) is false.
  • “8 dedicated outputs only”: ignores input-capable macrocell modes.


Common Pitfalls:

  • Assuming every right-side pin must be an output; many designs legally configure them as inputs.


Final Answer:
8 pins that are used as inputs or outputs.

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