Practical Coding Procedures
P. E. Gosling, Q. L. M. Laarhoven · 1980
One very suitable method for converting decimal numbers to binary number patterns is by a binary coded decimal (BCD) code. In a BCD code each decimal digit is converted into its binary equivalent and the resulting string of binary digits is used to represent the number. One such BCD code is the 8-4-2-1 code where the 8-4-2-1 refers to the weighting of the bit positions used. For example, the decimal number 851 is coded as 1000 0101 0001, whereas its full binary equivalent is 1101010011. Note the grouping of the binary digits into ‘tetrads’. The following table gives the ten tetrads used in the BCD coding of a decimal number.