binary coded decimal

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binary coded decimal

(BCD, packed decimal) A number representation where a number is expressed as a sequence of decimal digits and then each decimal digit is encoded as a four-bit binary number (a nibble). E.g. decimal 92 would be encoded as the eight-bit sequence 1001 0010.

In some cases, the right-most nibble contains the sign (positive or negative).

It is easier to convert decimal numbers to and from BCD than binary and, though BCD is often converted to binary for arithmetic processing, it is possible to build hardware that operates directly on BCD.

This article is provided by FOLDOC - Free Online Dictionary of Computing (


(Binary Coded Decimal) The storage of numbers in which each decimal digit is converted into a binary number and stored in a single 8-bit byte. For example, a 12-digit decimal number would be represented as 12 bytes. BCD uses more storage for numbers than binary encoding (see below). Prior to 8-bit bytes in the 1960s, BCD encoding used 6-bit characters. See binary numbers and byte.

BCD and Binary
The BCD method codes each decimal digit in binary and stores it in its own byte. The binary method converts the entire decimal number into a binary number. In the binary example above, the 1 in the left byte is the ninth bit starting from the rightmost bit in the right byte (1-2-4-8-16-32-64-128-256-512-1024-2048-4096-8192-16384-32768).

How Numbers Are Stored
BCD is one of four primary ways numbers are stored in the computer.
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TABLE I MAJOR SYNTHESIZER SPECIFICATIONS FOR THE AN/MPS-39 MOTR Frequency range (MHz) 1 to 250 Resolution (MHz) 0.2 Control binary-coded decimal Switching time ([[micro]seconds]) 6 Output level into 50 [ohms] (dBm) +10 Flatness (dB) [+ or -]0.5 Spurious signals (dBc) -68 Harmonics (dBc) -30 Phase noise (at any 105 at 100 Hz output frequency) 115 at 1 kHz (dBc/Hz) 123 at 10 kHz 127 at 100 kHz Switching behavior phase coherent Despite this definition, the assumption that all contemporary systems that use a single standard (external or internal) are coherent is incorrect.
From the user's perspective, the filter can be controlled using one of several digital interfaces, including binary-coded decimal, general-purpose interface bus (GPIB), RS-232, parallel and custom interfaces.