Latches and Flip-Flops:
Download: Latches and Flip-Flops Notes
- Latches and flip-flops are the basic elements for storing information.
- One latch or flip-flop can store one bit of information. The main difference between latches and flip-flops is that for latches, their outputs are constantly affected by their inputs as long as the enable signal is asserted.
- In other words, when they are enabled, their content changes immediately when their inputs change. Flip flops, on the other hand, have their content change only either at the rising or falling edge of the enable signal.
- This enable signal is usually the controlling clock signal. After the rising or falling edge of the clock, the flip-flop content remains constant even if the input changes.
- There are basically four main types of latches and flip-flops: SR, D, JK, and T. The major differences in these flip-flop types are the number of inputs they have and how they change state. For each type, there are also different variations that enhance their operations. In this chapter, we will look at the operations of the various latches and flipflops.
Latches:
A temporary storage device that has two stable states (bistable)
The S-R (Set-Reset) Latch (also called a multivibrator)
it is based on enable function input
it is a level trigerred , it mean that the output of present state and input of the next state depends on the level that is binary input 1 or 0.
When Q is HIGH, Q is LOW , and when Q is LOW, Q is high
Flip-Flops :
- Flip-flops are synchronous bistable devices known as bistable multivibrators
- They are edge triggered to insure a known transition point (although
- there have been some level triggered devices in the past)
- Their inputs change on a control input called the clock (CLK)
- All changes occur in sync with the clock input
There are basically four main types of flip-flops: SR, D, JK, and T. The major differences in these flip-flop types are in the number of inputs they have and how they change state. Each type can have different variations such as active high or low inputs, whether they change state at the rising or falling edge of the clock signal, and whether they have asynchronous inputs or not. The flip-flops can be described fully and uniquely by its logic symbol, characteristic table, characteristic equation, state diagram, or excitation table, and are summarized in Figure
