The BCD stands for Binary-Coded Decimal. It is a method of encoding decimal numbers where each individual decimal digit is represented by its own 4-bit binary sequence. For example, the decimal number 259 is represented in BCD as 0010 0101 1001, where 0010 is the binary for 2, 0101 is the binary for 5, and 1001 is the binary for 9. This contrasts with pure binary representation, where the entire number 259 would be converted to a single binary value, 100000011.
The primary advantage of BCD is the ease of conversion to and from human-readable decimal displays. It was widely used in early digital electronics, such as digital clocks and multimeters, because it simplifies the circuitry required to drive seven-segment displays. Each 4-bit BCD group can be directly mapped to a single decimal digit on the display. While BCD is less efficient in terms of data storage compared to pure binary (e.g., representing numbers up to 999 requires 12 bits in BCD, but only 10 bits in pure binary), its simplicity in handling decimal arithmetic and display made it valuable.
In the context of some older programmable instruments or specialized industrial controllers, data might still be transmitted or expected in BCD format. When writing control software for such devices, a programmer must perform the conversion between the computer's standard binary integer format and the BCD format required by the instrument.