Q.What is a BCD code?

The Binary Coded Decimal (BCD) and Excess-3 codes are the two most common ways of coding individual decimal digits for digital arithmetic.

In the standard 8-4-2-1 BCD code, each decimal digit from 0 to 9 is written as its ordinary 4-bit binary value. To code a multi-digit number, each decimal digit is converted separately; for example $823_{10} = 1000\;0010\;0011_{BCD}$. Because only ten of the sixteen possible 4-bit patterns are used, the combinations 1010 to 1111 are invalid in BCD. Converting back is just as direct — a BCD group is split into 4-bit fields and each field is read as one decimal digit. …