Digital clock design (HDL): purpose of the frequency prescaler In a 12-hour digital clock project, identify the main purpose of the prescaler (frequency divider) used ahead of the seconds counter.
-
Afind the basic frequency.
-
Btransform a 60 pps input to a 1 pps timing signal.
-
Cprevent the clock from exceeding 12:59:59.
-
Dallow the BCD display to have a value from 00–59.
Answer
Correct Answer: transform a 60 pps input to a 1 pps timing signal.
Explanation
Introduction / Context:Digital clocks require an accurate 1 pulse per second (1 pps) tick to advance seconds. Real-world reference sources (mains 60 Hz or crystals like 32.768 kHz) must be divided down to 1 Hz. The prescaler (frequency divider) performs this task, delivering a clean timing reference to the seconds counter.
Given Data / Assumptions:
- Clock reference might be 60 Hz (or 50 Hz, or a crystal frequency).
- Seconds counters advance on a 1 Hz enable pulse.
- We are focusing on the prescaler function, not on display range-limiting logic.
Concept / Approach:The prescaler divides a higher-frequency reference to the required base timing. For a 60 Hz mains reference, dividing by 60 produces 1 Hz (1 pps). This pulse then clocks the seconds unit counter reliably.
Step-by-Step Solution:
Identify reference: 60 pulses per second.Required tick: 1 pulse per second.Apply division: 60 / 60 = 1 pps.Feed 1 pps to seconds counter; other logic handles minutes/hours rollover.Verification / Alternative check:Designs using crystals (e.g., 32.768 kHz) similarly divide by powers of 2 to reach 1 Hz; concept is identical.
Why Other Options Are Wrong:
- A: The “basic frequency” is known; prescaler divides it, not finds it.
- C: Rollover logic limits 12:59:59, not the prescaler.
- D: BCD value ranges are enforced by counter modulus and decoding, not the prescaler.
Common Pitfalls:Mixing up prescaler duties with display decoding or hour/minute rollover logic.
Final Answer:transform a 60 pps input to a 1 pps timing signal.