Question 10.30: How will you form a BCD adder using the integrated circuit 4......

BCD adders can also be formed using the integrated circuit 4-bit binary adders. The problem is that when the sum of any group-of-four BCD exceeds 9 , or when there is a carry-out, the number is invalid and must be corrected by adding 6 to the invalid answer to get the correct BCD answer. (The valid range of B C D numbers is 0000 to 1001).

For example, adding 0111_{\mathrm{BCD}}+0110_{\mathrm{BCD}}(7+6) gives us an invalid result:

carry to next \mathrm{BCD} digit

The corrected answer is 00010011_{\mathrm{BCD}}, which equals 13.