Page 51 - Digital Electronics by harish

Example 2 : (54) 10 - (62) 10

Binary of 54 (Minuend) = 110110
Binary of 62 (Subtrahend) = 111110

1‟s complement of 111110 = 000001

Minuend 110110
Add 1‟s complement of Subtrahend + 000001
110111 There is no carry.
Find 1‟s complement
001000
- 001000 Result is negative.
Convert to Decimal - 8

Answer : - 8

Binary subtraction using 2’s complement method

The following steps are used to subtract a number using 2‟s complement method.

1) Find the 2‟s complement of the subtrahend.
2) Add the 2‟s complement with the minuend.
3) If there is any carry:
a. Ignore the carry
b. The result is a positive number.
4) If there is no carry:
a. Ignore the carry
b. Find the 2‟s complement of the result.
c. The result is a negative number.

Example 1 : Subtract 100101 from 101100

Here, the minuend is 101100
And the subtrahend is 100101

101100
- 100101
Difference

The 2‟s complement of subtrahend 100101 is 011011. This should be added to the minuend.

Minuend 101100
Add 2‟s complement of Subtrahend + 011011
1 000111 There is a carry 1.
Ignore it.
+ 000111 Result is positive.

Answer : + (111) 2

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