Question

What are the various methods used for triggering flip-flops? Explain with examples.

Answer 1

1. High Level Triggering

When a flip flop is required to respond at its HIGH state,  a HIGH level triggering method is used. It is mainly identified from the straight lead from the clock input. Take a look at the symbolic representation shown below.



2. Low Level Triggering

When a flip flop is required to respond at its LOW state,  a LOW level triggering method is used.. It is mainly identified from the clock input lead along with a low state indicator bubble. Take a look at the symbolic representation shown below.



3. Positive Edge Triggering

When a flip flop is required to respond at a LOW to HIGH transition state,  POSITIVE edge triggering method is used. It is mainly identified from the clock input lead along with a triangle. Take a look at the symbolic representation shown below.



4. Negative Edge Triggering

When a flip flop is required to respond during the HIGH to LOW transition state,  a NEGATIVE edge triggering method is used.. It is mainly identified from the clock input lead along with a low-state indicator and a triangle. Take a look at the symbolic representation shown below.



Clock Pulse Transition

The movement of a trigger pulse is always from a 0 to 1 and then 1 to 0 of a signal. Thus it takes two transitions in a single signal. When it moves from 0 to 1 it is called a positive transition and when it moves from 1 to 0 it is called a negative transition. To understand more take a look at the images below.



The clocked flip-flops already introduced are triggered during the 0 to 1 transition of the pulse, and the state transition starts as soon as the pulse reaches the HIGH level. If the other inputs change while the clock is still 1, a new output state may occur. If the flip-flop is made to then the multiple-transition problem can be eliminated.

The multi-transition problem can be stopped is the flip flop is made to respond to the positive or negative edge transition only, other than responding to the entire pulse duration.