latch and flip flop

[Badar]

I wonder if somebody tells me the difference b/w a flip flop and latct.
I have read some of the books and one of them states that basic difference b/w the two is of clock signal.
But in other book i've seen the topic like S-R latch but in other it is S-R flip flop.One has the topic named CLOCKED S-R LATCH and some have clocked S-R flip flop.
Doesn't this imply that we may have a clocked latch and will still say it a latch

 

[dknguyen]

If I remember right, a flip-flop output is always "latched" and on the signal on the rising edge of the clock the output gets latched to the new input and never really becomes transparent. While a latch can becomes transparent when the clock is low, and latches when the clock goes high (level-triggered not edged triggered). You could also call the clock a control signal. Doesn't have to periodic.

Basically,
FF = edge-triggered, never transparent
Latch = level-triggered, can be transparent

Both have a control signal which may or may not be a clock. I never really understood this until after my digital logic course, heh.

 

[Leftyretro]

A latch is simply a storage element. Any flip flop can act as a single bit storge element, however a simple latch cannot perform all the functions that a flip flop can, like as a divide by 2 element.

Triggering, edge or level, leading or training edge or both edges as in a J-K FF, is specific to a given IC design and does not define the circuit as a latch or a FF.

Lefty

 

[philba]

Yes, the terms (latch and FF) are not exact. there are several kinds of FFs and latches. Look at the datasheet of the specific device you are considering.

 

[Badar]

I had to continue this topic again cuz after sufficient reading i still find my self without a conclusion about the concept of latch and Flip Flops.
Here are some references that i think are contradicting.

Digital Fundamentals 7th edition by FLOYD (page 394)
"The latch is a type of temporaray storage device that has two stable states (bistable) and is normally placed in a category separate from that of flip flops.Latches are basically similar to flip flops because they are bistable devices that can reside in either of two states using a feedback arrangement,in which the outputs are coneected back to the opposite inputs.The main difference between latches and flip flops is in the method used for changing their state."

Digital electronics Principles and Applications by ROGER L. TOKHEIM (page 217) states the R-S latch and R-S Flip Flop the same thing.

And while googling and reading some other material i found that the main difference b/w both of them is of clock signal.i.e a flip flop without a clock input is a latch.

Another book states SCR as a type of latch when i was reading SCR's

Now i conclude from all these contradicting statements that latching is a phenomenon which all flip flops exhibit.But the flip flops which have only one function (i.e latching) are called latches.
Or the flip flops which have such an arrangement that one output is directly given to opposite input as a feedback is called a latch.

Now i wanna confirm this conclusion.What you people say about that.

 

[Leftyretro]

I had to continue this topic again cuz after sufficient reading i still find my self without a conclusion about the concept of latch and Flip Flops.
Here are some references that i think are contradicting.

Digital Fundamentals 7th edition by FLOYD (page 394)
"The latch is a type of temporaray storage device that has two stable states (bistable) and is normally placed in a category separate from that of flip flops.Latches are basically similar to flip flops because they are bistable devices that can reside in either of two states using a feedback arrangement,in which the outputs are coneected back to the opposite inputs.The main difference between latches and flip flops is in the method used for changing their state."

Digital electronics Principles and Applications by ROGER L. TOKHEIM (page 217) states the R-S latch and R-S Flip Flop the same thing.

And while googling and reading some other material i found that the main difference b/w both of them is of clock signal.i.e a flip flop without a clock input is a latch.

Another book states SCR as a type of latch when i was reading SCR's

Now i conclude from all these contradicting statements that latching is a phenomenon which all flip flops exhibit.But the flip flops which have only one function (i.e latching) are called latches.
Or the flip flops which have such an arrangement that one output is directly given to opposite input as a feedback is called a latch.

Now i wanna confirm this conclusion.What you people say about that.

Well as the prior poster stated, it's better to just study the data sheets for various specific flip/flop devices then it is to try to come up with universal statements about this family of devices, at least in my opinion

Lefty

 

[Badar]

Well as the prior poster stated, it's better to just study the data sheets for various specific flip/flop devices then it is to try to come up with universal statements about this family of devices, at least in my opinion

Lefty

I m trying to find the exact answer of this just because you can say it's my viva question.And i don't wanna be beaten this time

 

[Bob Scott]

If I remember right, a flip-flop output is always "latched" and on the signal on the rising edge of the clock the output gets latched to the new input and never really becomes transparent. While a latch can becomes transparent when the clock is low, and latches when the clock goes high (level-triggered not edged triggered). You could also call the clock a control signal. Doesn't have to periodic.

Basically,
FF = edge-triggered, never transparent
Latch = level-triggered, can be transparent

I looked this up in my databooks a few years ago. You are correct Mr Nguyen. The only difference between a quad D FF and a quad D latch is that the FF is edge triggered. The datasheets are identical except for clock specs.

Unfortunately I forgot the exact 4000 series part numbers.