Digital clock indicator logic: when should the PM indicator assert (go HIGH)? In a 12-hour digital clock, identify the exact time transition at which the PM indicator should change state from LOW to HIGH.

Introduction / Context:
A 12-hour clock toggles its AM/PM indicator at noon and midnight. Correctly placing the transition is important to avoid off-by-12-hours display bugs when minutes and hours roll over.

Given Data / Assumptions:

• AM corresponds to times 12:00:00 through 11:59:59 of the first half-day.
• PM corresponds to times 12:00:00 through 11:59:59 of the second half-day.
• We consider the exact second-level transition.

Concept / Approach:
The PM indicator asserts at the instant the clock moves into the afternoon period: precisely at 12:00:00 noon (following 11:59:59 AM). It deasserts at midnight (12:00:00 AM) when the cycle restarts.

Step-by-Step Solution:

Verification / Alternative check:
Truth table of AM/PM over a 24-hour period confirms toggles only at the two 12:00:00 transitions.

Why Other Options Are Wrong:

• A: The indicator certainly toggles twice per day.
• C: 12:59:59 to 01:00:00 does not change AM/PM.
• D: Refers to a signal edge rather than the time-state boundary.

Common Pitfalls:
Incorrectly toggling at 11:59:59 or 12:00:01 introduces a one-second display error.

Final Answer:
Going from 11:59:59 to 12:00:00