BCD code - definition
BCD code - definition
BCD code (binary-coded decimal) is a way of representing decimal numbers in the binary system, in which each decimal digit (0 to 9) is encoded separately as a four-bit binary number. Unlike classical binary coding, in which the whole number is converted to binary as a whole, the BCD code treats each decimal digit as an independent unit, which facilitates the direct representation of numeric data in human-operated digital devices such as seven-segment displays, counters or terminals.
In the most commonly used variant, called 8421 BCD, each decimal digit is mapped by a four-bit code corresponding to its value, with only combinations from 0000 (for 0) to 1001 (for 9) allowed. Others four possible bit combinations (1010 to 1111) are not used in classical BCD and can lead to interpretation errors if not handled properly. There are also other versions of the BCD encoding, e.g. packed BCD, zoned BCD or excess-3, which differ in data structure and application to specific hardware architectures or transmission systems.
The BCD code is particularly useful in systems that need to provide easy conversion between binary and decimal representation, without the need for complex conversion algorithms. This facilitates the implementation of input-output operations in microprocessor systems, industrial Automation and real-time systems. Although the BCD representation is less efficient in terms of memory usage and bandwidth than pure binary notation, its readability and simplicity of conversion to a human-understandable form make it practical for many engineering applications.
In digital systems, BCD arithmetic requires the use of special correction circuits because the sum of two digits in the BCD code can exceed the allowable four-bit range. Therefore, electronic circuits performing BCD operations often include additional logic to control the correctness of the notation and result.
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