Q. Binary Coded Decimal Addition

Now as in conventional decimal addition, Binary Coded Decimal addition is performed one decimal digit at a time.

What happens when the sum go above what can be represented in 4 bits?

What are the circumstances under which a carry is generated to the next highest-order BCD digit?

For illustration, let's consider the addition of the two BCD digits 5 and 3:

Now consider the sum of 5 and 8:

The sum is 1101₂ = 13, but this result should be properly represented as 0001 0011 in Binary Coded Decimal notation. Auspiciously, there is a simple way to find the correct result. We add 6 (0110₂) to the digit sum if it exceeds 9

. Let's examine the following cases:

In the both cases, by adding six we obtain the correct answer in BCD.