# Advantages and disadvantages of binary coded decimal

In the event that an invalid entry any BCD digit greater than exists, 6 is added to generate a carry bit and cause the sum to become a valid entry. The latter has the advantage that subsets of the encoding encode two digits in the optimal seven bits and one digit in four bits, as in regular BCD. Programmable calculators manufactured by Texas Instruments advantages and disadvantages of binary coded decimal, Hewlett-Packardand others typically employ a floating-point BCD format, typically with two or three digits for the decimal exponent. In signed BCD, is Densely packed decimal is a similar scheme that is used for most of the significandexcept the lead digit, for one of the two alternative decimal encodings specified in the IEEE standard.

Various BCD implementations exist that employ other representations for numbers. For example, to represent the decimal number in packed BCD, using big-endian format, a program would encode as follows:. A "12 zone" punch set both B and Aan "11 zone" set Band a "0 zone" a 0 punch combined with any others set A.

The decimal point is not actually stored in memory, as the packed BCD storage format does not advantages and disadvantages of binary coded decimal for it. Computer arithmetic Numeral systems Non-standard positional numeral systems Binary arithmetic. Bensonthe U. As with two's complement binary numbers, the range is not symmetric about zero. This allows the circuitry to convert between the punched card format and the internal storage format to be very simple with only a few special cases.

By employing BCD, the manipulation of numerical data for display can be greatly simplified by treating each digit as a separate single sub-circuit. A variable length Packed BCD numeric data type is also implemented, providing machine instructions that perform arithmetic directly on packed decimal data. Advantages and disadvantages of binary coded decimal of the simple sum of two digits can be done by adding 6 that is, 16 — 10 when the five-bit result of adding a pair of digits has a value greater than 9.

Each decimal digit is stored in one byte, with the lower four bits encoding the digit in Advantages and disadvantages of binary coded decimal form. BCD is very common in electronic systems where a numeric value is to be displayed, especially in systems consisting solely of digital logic, and not containing a microprocessor. As an example, a 4-byte value consists of 8 nibbles, wherein the upper 7 nibbles store the digits of a 7-digit decimal value and the lowest nibble indicates the sign of the decimal integer value. If a decimal digit requires four bits, then three decimal digits require 12 bits.

January Learn how and when to remove this template message. Most pocket calculators do all their calculations in BCD. Subtraction is done by adding the ten's complement of the subtrahend. Conversion of the simple sum of two digits can be done by adding 6 that is, 16 — 10 when the five-bit result of adding a pair of digits has a value greater than 9. To represent the sign of a number in BCD, the number is used to represent a positive advantages and disadvantages of binary coded decimaland is used to represent a negative number.

If a decimal digit requires four bits, then three decimal digits require 12 bits. The same argument applies when hardware of this type uses an embedded microcontroller or other small processor. All of these are used within hardware registers and processing units, and in software.

Note that, like character strings, the first byte of the packed decimal — with the most significant two digits — is usually stored in the lowest address in memory, independent of the endianness of the machine. Some Advantages and disadvantages of binary coded decimal provide a half-carry flag to facilitate BCD arithmetic adjustments following binary addition and subtraction operations. Therefore, in cases where the calculations are relatively simple, working throughout with BCD can lead to a simpler overall system than converting to and from binary.

Conversion of the simple sum of two digits can be done by adding 6 that is, 16 — 10 when the five-bit result of adding a pair of digits has a value greater than 9. BCD alphamerics are encoded using digit pairs, with the "zone" in the even-addressed digit and the "digit" in the odd-addressed digit, the "zone" being related to the 1211and 0 "zone punches" as in the series. This matches much more closely the physical reality of display hardware—a designer might choose to use a series of separate identical advantages and disadvantages of binary coded decimal displays to build a metering circuit, for example.

Burroughs systems used D for negative, and any other value is considered a positive sign value the processors will normalize a positive sign to C. The following table represents decimal digits from 0 to 9 in various BCD systems:. These characters vary depending on the local character code page setting. To correct this, 6 is added to that advantages and disadvantages of binary coded decimal and then the result is treated as two nibbles:. BCD is very common in electronic systems where a numeric value is to be displayed, especially in systems consisting solely of digital logic, and not containing a microprocessor.