* Excess-3 code is non-weighted and self complementary code.
A self complementary binary codes are always compliment themselves.
The complement of a binary number can be obtained from that number by replacing 0’s with 1’s and 1’s with 0’s.
The sum of binary number and its complement is always equal to decimal 9.
In other words, the 1’s complement of an excess-3 code is the excess-3 code for the 9’s complement of the corresponding decimal number.
For example, the excess-3 code for decimal number 5 is 1000 and 1’s complement of 1000 is 0111, which is excess-3 code for decimal number 4, and it is 9’s complement of number 5.