Add two signed numbers examples below.

EX1: -7, +6 : Two negative numbers.

-7 +6

Step 1: Convert to 2's complement for negative numbers.

-7 (in Binary 4’b1111) = 1 001, save msb as sign bit and convert lower 3 bits into 2’s complement.

+6 (in Binary 4’b0110).

Step 2

Add and store the result in sum register of 5 bits wide.

1 001

0 110

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1 111

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Step 3

No carry into signed bit and no carry out of signed bit. In this scenario keep MSB as sign and take 2’s complement of lower 3 bits.

Result: 4’b1 001 = 0x11 = -1