# Simple question on clock signal

#### MichealY

Joined Apr 9, 2009
49
Hi,
I'm pretty new to this field and the question about clock signal really makes me frustrated for a long time.So could you help me?

Why do we need the clock signal most of the time,for example,flip-flops?Why dont we need the clock signal under other circumstances,for example,latches?

MichealY

#### beenthere

Joined Apr 20, 2004
15,808
Briefly, a latch holds data presented to it at random intervals. Flip flops tend to be organized to work together with other logic elements, and need to change state at predictable times, so they get clocked.

#### Wendy

Joined Mar 24, 2008
21,840
A digital clock, as in alarm clock, is a good example. If it doesn't get clocked it doesn't count, which is what it is for, counting time.

Computers use clocks to move to the next instruction, it is what makes the program move along.

#### GetDeviceInfo

Joined Jun 7, 2009
1,623
If it helps;

Think of a mechanical machine where you put something in one end, crank the handle around once, and the thing comes out the other end with something being done do it.

In this analogy, the single crank of the handle applies some work process to the object. In electronics, the single crank of the handle is your clock.

If you want a single process to take place, you crank once. When you want your electronic device to perform it's task, you 'clock' the device.

Going back to the machine, if you have a production line where the object is feed continuosly into the machine, you want the crank to turn every time something is fed in, at some rate. In electronics then, you apply the clock in a pulse stream.

This analogy is not completely accurate however, as in the machine work is typically taking place during the entire rotation of the crank. In your electronics the action takes place on the clocks transition. Keep this in mind and look for what transition is required by the device. It will be either the high to low transition or the low to high transition.

#### zimbarak

Joined Feb 8, 2009
56
as a reaply for your Q ? in flips flops we dont basically need a clock coz the flips flops is already a clock generator ! so its generate the clock by itself ! in latch or latch d register we need a clock signal to save the input level dependant of the clock signal !

#### MichealY

Joined Apr 9, 2009
49
Thanks to all of you guys.
It save me a lot of time to understand this mystery.I think I should do some design then I will know this throughly.

And If could,could you give some real-world examples to explain why we need clock signal.

MichealY

#### beenthere

Joined Apr 20, 2004
15,808
Of course - a computer.

#### Wendy

Joined Mar 24, 2008
21,840
A digital clock. Any process that chugs along.

#### zimbarak

Joined Feb 8, 2009
56
if u want to understand more the clock signal try to build a small circuits on pspice such as adding manny latch d memory or jK as well together serial or parallel !

#### Beduin

Joined May 20, 2009
16
Soldiers need a drum to march?