What is ab c d 4
BCD code - Binary Coded Decimals
In addition to the number systems, there are also codes to represent and process numbers digitally. The BCD code stands for Binary Coded Decimals, which means binary coded decimal digits. What is meant are dual-coded numbers. In the BCD code, each decimal digit is represented by 4 bits of the corresponding dual number.
Another name is 8-4-2-1-BCD-Code, because it is the decimal value of the dual digits.
Each decimal digit of the decimal number is expressed by its own 4-bit binary number or binary code. The 4 bits are called a tetrad (Greek: group of four).
Only 10 tetrads are required for the 10 decimal digit. The 6 other tetrads are called pseudotetrads and no longer belong to them. They are omitted or have no function. They do not appear or must not appear in the BCD code.
Example of a two-digit decimal number
|0 0||0000 0000|
|0 1||0000 0001|
|0 2||0000 0010|
|0 3||0000 0011|
|0 4||0000 0100|
|0 5||0000 0101|
|0 6||0000 0110|
|0 7||0000 0111|
|0 8||0000 1000|
|0 9||0000 1001|
|1 0||0001 0000|
|1 1||0001 0001|
|1 2||0001 0010|
|1 3||0001 0011|
|1 4||0001 0100|
|1 5||0001 0101|
|1 6||0001 0110|
|1 7||0001 0111|
|1 8||0001 1000|
|1 9||0001 1001|
|2 0||0010 0000|
|2 1||0010 0001|
|2 2||0010 0010|
|2 3||0010 0011|
Identification of the BCD code
Bit sequence: 1001 = 1001BCD = 910
Bit sequence: 1000111 = 0100 0111BCD = 4710
Disadvantage of the BCD code
For a three-digit decimal number from 0 to 999 you would need 10 bits as the binary number (11111001112). 12 bits are required as a binary coded decimal number (0011 1110 0111BCD).
Therefore, in practice, instead of BCD, other codes are used that are not so wasteful.
BCD arithmetic is rarely used. The memory is being used too wastefully. And compared to 32-bit floating point numbers, BCD numbers only provide a slightly higher level of precision. However, there is still a need in finance and science for very high accuracy that goes beyond floating point representation. There is, for example, Densely Packed Decimal Encoding, which is supported by the hardware on some computers or is available via software libraries. For mainframe computers as well as technical-scientific pocket calculators.
BCD coding is used in digital technology and digital displays. For example as a 7-segment display.
Digital clocks run inside with BCD code. The time in the DCF77 signal is also encoded as a BCD code.
A BCD decoder and a 7-segment display are used to display the 4-bit binary number as a decimal number. The 7-segment display has 7 light strips that are arranged like an 8. The BCD decoder decodes the BCD code (4-bit) to the 7 segments.
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