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Multiplication overflow detector!

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manikmalhotra92

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Q:I had been given a question in my exam which said that one had to design a circuit that will find the twice of a 4 bit number , condition that whenever the result exceeds an outpout of 15 "OVERFLOW"(O) should become high!
My answer:
Code: 
       Inputs                                      Outputs
  (LSB)A  B C D(MSB)                              O E F G H
       0  0 0 0                                   0 0 0 0 0
       0  0 0 1                                   0 0 0 1 0                           
       0  0 1 0                                   0 0 1 0 0
       0  0 1 1                                   0 0 1 1 0
       0  1 0 0                                   0 1 0 0 0
       0  1 0 1                                   0 1 0 1 0
       0  1 1 0                                   0 1 1 0 0
       0  1 1 1                                   0 1 1 1 0
       1  0 0 0                                   1 0 0 0 0
       1  0 0 1                                   1 0 0 1 0
       1  0 1 0                                   1 0 1 0 0
       1  0 1 1                                   1 0 1 1 0
       1  1 0 0                                   1 1 0 0 0
       1  1 0 1                                   1 1 0 1 0
       1  1 1 0                                   1 1 1 0 0
       1  1 1 1                                   1 1 1 1 0

from the table:
O(OVERFLOW)=A
E=B
F=C
G=D
H=0

so The Circuit:
A--------------Buffer------------->Overflow
B--------------Buffer------------->E
C--------------Buffer------------->F
D--------------Buffer------------->G
0--------------Buffer------------->H
is this correct?
 

where is the circuit?

you have to design a 4 bit adder circuit
 

betwixt said:
Each binary bit has twice the value of the preceding one so yes, shifting the bits to the left by one place doubles the value and the MSB becomes the carry bit.

Brian.
Click to expand...

So simple connections would work??
 

you need a 4bit adder , check this site

**broken link removed**
 

Radjup, why do you think an adder is needed? To double a binary number all you have to do is shift it left. If it was adding two numbers, either the same or different ones I would agree with you but multiplication by 2 is much simpler.

Brian.
 

yes you are right, it can be done but what i thought a simple shift won't help here for low bit if input 1 output will be 0 but the carry has to be added to the 1st bit and so on

as per the table given simple shift will do
 

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