Decoders — Required Enable Conditions For reliable operation of a generic 1-line-to-16-line (4-to-16) decoder, what enable condition is typically required before decoding can occur?

Introduction / Context:
Most decoder ICs include one or more enable (EN) inputs that globally allow or inhibit outputs. This permits chip-select functionality, output gating, and expansion (cascading multiple decoders). Understanding the required enable state ensures that the device actually performs decoding when expected.

Given Data / Assumptions:

• Device: a 4-to-16 decoder (often described as 1-of-16).
• Enable inputs are present and must be in the active state to pass decoded outputs.
• Exact polarity of enables varies by family, but the principle remains: enables must be active.

Concept / Approach:
In many common parts (e.g., 74HC154), enables are active-LOW; in others (e.g., selected programmable logic), they may be active-HIGH. The question is phrased generically, so the correct conceptual answer is that the enable inputs must be in their active (asserted) state. In the provided options, this corresponds to “a HIGH on all gate enable circuits.”

Step-by-Step Solution:
Identify the role of EN: it globally permits output assertion.Determine the generic condition: EN must be asserted (active).Map to given choices: the only answer expressing “asserted/active” in general terms is “a HIGH on all gate enable circuits.”Therefore, decoding proceeds when enables are active.

Verification / Alternative check:
Datasheets show that with EN deasserted, all outputs are disabled (often all HIGH or all LOW depending on the device), regardless of the input code. With EN asserted, the one-of-16 output becomes active per the input lines.

Why Other Options Are Wrong:

• a LOW on all gate enable inputs: Only correct for parts with active-LOW EN; the question is generic.
• input from a hexadecimal counter: A possible source of input data, not an enable condition.
• flasher circuit control signal: Irrelevant to decoder operation.

Common Pitfalls:
Forgetting to drive enables, or assuming enables are always active-HIGH. Always check the polarity in the specific part’s datasheet.

Final Answer:
a HIGH on all gate enable circuits