---
title: "Level vs edge triggering"
subject: "Digital Logic"
chapter: 6
key: "semester_3/digital_logic:level-vs-edge-triggering"
source: https://www.bctengineer.com/q/semester_3/digital_logic/level-vs-edge-triggering
site: BCT Engineering
---

# Level vs edge triggering

Digital Logic · Chapter 6: Flip Flops

- Asked in: 2076 Asoj; 2070 Chaitra, 3 marks (asked 2 times)
- Video: [Lec -33: Level Trigger vs Edge Trigger Flip Flop | Types of Triggering](https://www.youtube.com/watch?v=SK0bSphgBgI) — Gate Smashers
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/digital_logic/level-vs-edge-triggering
- Whole chapter: https://www.bctengineer.com/md/semester_3/digital_logic/chapter-6

## Question

Differentiate between level and Edge triggering?

## Short answer

Level triggering makes the output respond to inputs during the entire active clock level (HIGH or LOW), while edge triggering responds only at the instant of a clock transition (rising or falling edge). Latches use level triggering and may change multiple times per clock; flip-flops use edge triggering, changing at most once per cycle, avoiding race-around and reducing noise sensitivity.

## Answer

**Triggering** is the way a clock signal makes a flip-flop or latch change state. In **level triggering** the output responds to the inputs during the whole time the clock is at its active level (HIGH or LOW). In **edge triggering** the output responds only at the instant of a clock transition (rising or falling edge).

```text
CLK      ___|‾‾‾‾‾‾‾|___
Level:      [ active ]     (whole HIGH time)
+ve edge:   ^              (only at rise)
-ve edge:           v      (only at fall)
```

| Point | Level triggering | Edge triggering |
|---|---|---|
| Responds | During whole active level | Only at clock edge |
| Device | Latch (gated SR, D latch) | Flip-flop |
| Symbol | Plain CLK / EN input | Triangle (>) at CLK; bubble for falling |
| Output changes | Many times in one clock pulse | At most once per clock cycle |
| Race-around | Possible (JK with J=K=1) | Not possible |
| Noise sensitivity | More (any glitch during level) | Less |
| Use | Simple storage, transparent latches | Counters, shift registers, synchronous systems |

Example: in a D latch with $EN = 1$, Q follows D continuously ("transparent"). In a positive-edge D flip-flop, Q takes the value of D only at the rising edge and holds it until the next rising edge.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What is the basic difference between level and edge triggering?
   A. Level triggering responds during the whole active level; edge triggering only at a clock transition
   B. Both respond only at transitions
   C. Level triggering responds only at a clock transition; edge triggering responds during the whole level
   D. Level triggering needs no clock
   Answer: A. Level-triggered devices act for as long as the clock is at its active level; edge-triggered ones act at the instant of the transition. (Key point: Definition)

2. Which statement about race-around is correct?
   A. Never happens in any JK
   B. Possible in level-triggered JK with J = K = 1; not possible in edge-triggered
   C. Possible in edge-triggered JK
   D. Happens only in D flip-flops
   Answer: B. A level-triggered JK can toggle repeatedly while the clock stays active; edge-triggering allows at most one change per cycle. (Key point: Race-around)

3. Which is correct?
   A. Both have a triangle at CLK
   B. A bubble with the triangle means level triggering
   C. Latch is level-triggered; flip-flop is edge-triggered with a triangle at CLK
   D. Latch is edge-triggered; flip-flop is level-triggered
   Answer: C. Latches (gated SR, D latch) are level-triggered; edge-triggered flip-flops show a triangle, with a bubble for the falling edge. (Key point: Devices and symbols)

## Related in Digital Logic

- [Digital system, logic level, BCD vs binary](https://www.bctengineer.com/question.md?key=semester_3%2Fdigital_logic%3Adigital-system-logic-level-bcd) — Digital Logic, chapter 1
- [Asynchronous mod-12 down counter](https://www.bctengineer.com/question.md?key=semester_3%2Fdigital_logic%3Aasync-mod12-down-counter) — Digital Logic, chapter 8
- [Comb vs seq; asynchronous decade counter](https://www.bctengineer.com/question.md?key=semester_3%2Fdigital_logic%3Aasync-decade-comb-seq) — Digital Logic, chapter 8, asked 4×
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- [Sync vs async; mod-12 synchronous counter](https://www.bctengineer.com/question.md?key=semester_3%2Fdigital_logic%3Amod12-synchronous-counter) — Digital Logic, chapter 8, asked 3×
- [Comb vs seq; synchronous decade counter](https://www.bctengineer.com/question.md?key=semester_3%2Fdigital_logic%3Async-decade-comb-seq) — Digital Logic, chapter 8, asked 2×

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