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Signed numbers in Decimal 
4 bit Signed Representation. bit[3] = signed value, bit[2:0] = value after sign bit bit[3] = 1 when sign ‘ bit[3]=0 when sign ‘+’ 
Representation of negative numbers as 2’s complement. bit[3:0] = value. bit[4] as 0. 
7 
4’b0111 
UNCHANGED 
6 
4’b0110 

5 
4’b0101 

4 
4’b0100 

3 
4’b0011 

2 
4’b0010 

1 
4’b0001 

0 
4’b0000 

 
4’b1001 
3’b111 
 
4’b1010 
3’b110 
 
4’b1011 
3’b110 
 
4’b1100 
3’b100 
 
4’b1101 
3’b011 
 
4’b1110 
3’b010 
 
4’b1111 
3’b001 
Binary addition of signed numbers
Signed number is a way of representing positive & negative numbers in binary form where most significant bit(MSB) signifies sign.
In table below positive and negative numbers in range 
Examples related to signed magnitude are discussed next.
Examples to add four possible combinations of two signed numbers.
EX1: 
EX2: +7, 
EX3: 
EX4: +7, +6 : Two positive numbers