BCD Addition |Binary coded decimal | Binary codes Malayalam

In Binary coded decimal BCD decimal numbers (0,1,2...9) represented by four digit binary number. 4 digit numbers greater than 9 1010,1011,1100,1101,1110,1111 are invalid in BCD.
Add two BCD numbers using binary addition. If 4 bit sum is equal or less than 9, it is a valid BCD number. If 4 bit sum greater than 9, add 6 ( 0110) to it and pass carry to next digit until all digits are valid BCD.