when can we use Flip flops to design Binary adder ?

[dhanya22]

Hello

I want to know when is it necessary to design Adder using flip flops or where is it used ?

Regards

 

[BrunoARG]

Give us more information, the question is not clear.

 

[dick_freebird]

The adder function is all combinatorial. Registers just
make the data flow orderly and eliminate intermediate
bogus output states as the paths may have varying
delays.

 

[dhanya22]

Hello, Thanks for the answer

Actually I am asked to use flip fops for making an adder as an assignment.
I want to know where would such condition exist ? I mean are Flip Flops( which are sequential) used to design adder (which is combinational.) ?

 

[Y.SAI SARASWATHI]

Hello,
Combinational circuits can be realized using sequential blocks,
similar to truth table in combinational design, use state transition tables and then design input equations for each flip flop using corresponding excitation tables of flip flops.
if required use control inputs of each flip flop to control asynchronously.

 

[darkgnat]

You generally use combinational logic to create adders. You latch the output with flip flops to keep the value "safe" for a particular clock cycle, otherwise you will get spurious values as the adder is a finite device and it takes a while for the proper value to propagate to the output because of logic gate and conductor delays. There are ways to create safe asynchronous adders but I suspect that is beyond what you are doing or studying and require it's own additional logic.

 

[burrow]

Well i think u can have a 4 bit adder using a singe FULL adder combinational circuit and couple of flipflops. I think its called serial adder or something. Its working is like this, first the full adder circuit will add lsb of the given number and the carry is stored in a flipflop and sum is given as output ( or again can be stored in a another register ) and then again next bit is added along with the carry from previous operation

 

[dhanya22]

Hello

Can you give an example for explanation purpose

 

[burrow]

Yea lets say we need to add 4 bit numbers



One shift register stores addent bit and the other stores augend bits.
They shift out 1 bit to the adder. adder adds them and then send the sum to another shift register and carry is stored in a flipflop which is then added along with next 2 bits.