Electronics and Communication Engineering - Digital Electronics - Discussion

At all many have a doubt for the negative sign doubt so I ll try to solve it.

In digital electronics the MSB bit (the leftmost bit) is the sign bit and its negative if it is set to 1 or if it is set to 0 it is positive. So look at the MSB perform the operation and represent it as positive or negative depending on the sign bit.

If carry is generated find 2's complement of the answer to get final result,

If carry is not generated give negative sign and write the value.

It should be +27.

How it comes in negative.

The MSB holds the sign.

2's complement means only negitive number. If we take 2's complement of 011 then it means negitive of 011.

A = 11100101.
Therefore A = 00011010 and A' = A + 1 = 00011011 = 16 + 8 + 2 + 1 = 27.
Therefore A = -27.

In any question or statement, if it is stated that it's a 2's complement, then it's obvious that the MSB is a sign bit, 0 for a positive and 1 for a negative number. In 2's complement form, if any number starts from 1, then it's a negative number, which is the case here.
So, for calculating the magnitude of the 2's-complement number, we have to take the 2's complement of the given 2's complement itself, and that will give us the magnitude only, not the sign.
The sign will be the original sign, which was before calculating the magnitude, so here the magnitude is 27, but the sign is negative.
The answer comes as -27.

2's com -11100101. Then 1's com is 11100101-1=1100100.

Then the required binary no is 0011011. According to binary to decimal conversion the position value is 128, 64, 32, 16, 8, 4, 2, 1 here binary 1 is present in 16+8+2+1=27.

The first no 1 indicates the -ve number.