HDL digital clock design: At 11:59:59, the detection logic (for example, an AND gate that monitors the tens-of-hours = 1 along with other roll-over conditions) and the edge-triggered clock together advance the display to 12:00:00. Evaluate this implementation detail.

Introduction / Context:
Digital clock projects in HDL (Hardware Description Language) commonly implement hour, minute, and second counters with well-defined roll-over conditions. The transition from 11:59:59 to 12:00:00 in a 12-hour clock requires special detection logic so that hours advance from 11 to 12, not to 00, preserving familiar timekeeping conventions.

Given Data / Assumptions:

• Format: 12-hour display with hours = 01…12.
• At 11:59:59, the counters for seconds and minutes are at 59, and the hour is 11 (tens-of-hours = 1 and ones-of-hours = 1).
• Edge-triggered clocking updates the registers synchronously on the active clock edge.

Concept / Approach:
In HDL, roll-over is handled by decoding a terminal count and issuing a synchronous load or increment. An AND gate (or equivalent Boolean term) often watches a combination of states: seconds = 59, minutes = 59, hours = 11. When that condition is true at the next clock edge, the control logic forces seconds and minutes to 00 and loads hours with 12 rather than incrementing to 00.

Step-by-Step Solution:
Detect terminal count: (sec == 59) * (min == 59) * (hours == 11).Include sub-decodes: tens_of_hours == 1 and ones_of_hours == 1.On the edge-triggered clock, execute: sec := 00; min := 00; hours := 12.Else, operate normally: seconds increment; cascade to minutes and hours on overflow.

Verification / Alternative check:
Simulate a timing wave: advance time through 11:59:58 → 11:59:59 → 12:00:00. Confirm synchronous loads occur only on the clock edge when the AND condition is true.

Why Other Options Are Wrong:
“Incorrect” ignores the standard 12-hour roll-over logic. “Only for 24-hour clocks” is inverted; 24-hour uses 23→00. The conditions do not require “minutes tens = 0.” “Asynchronous clocks” are not required; synchronous, edge-triggered design is the norm.

Common Pitfalls:
Forgetting to load 12 after 11, accidentally rolling to 00, or mixing asynchronous resets with synchronous loads causing glitches.

Final Answer:
Correct