Aiken code
Complementary binary-coded decimal code
The Aiken code (also known as 2421 code) is a complementary binary-coded decimal (BCD) code. A group of four bits is assigned to the decimal digits from 0 to 9 according to the following table. The code was developed by Howard Hathaway Aiken and is still used today in digital clocks, pocket calculators and similar devices.
The Aiken code differs from the standard 8421 BCD code in that the Aiken code does not weight the fourth digit as 8 as with the standard BCD code but with 2.
The following weighting is obtained for the Aiken code: 2-4-2-1.
One might think that double codes are possible for a number, for example 1011 and 0101 could represent 5. However, here one makes sure that the digits 0 to 4 are mirror image complementary to the numbers 5 to 9.
| Aiken code | |||
|---|---|---|---|
| Decimal digit |
Aiken 2 4 2 1 code | ||
| 0 | 0 0 0 0 | ||
| 1 | 0 0 0 1 | ||
| 2 | 0 0 1 0 | ||
| 3 | 0 0 1 1 | ||
| 4 | 0 1 0 0 | ||
| 5 | 1 0 1 1 | ||
| 6 | 1 1 0 0 | ||
| 7 | 1 1 0 1 | ||
| 8 | 1 1 1 0 | ||
| 9 | 1 1 1 1 | ||
Sources and credits
This article is adapted from the Wikipedia article “Aiken code”, written by its contributors and licensed under CC BY-SA 4.0. Fathomly has changed the layout, removed citation markers, navigation and maintenance notices, and adjusted punctuation. This adapted version is shared under the same license. For references, see the original article.
Images, from Wikimedia Commons:
- AikenCode.png by snipermatze, CC BY-SA 3.0
- Aiken codetafel symmetrie.PNG by N-twickler, Public domain
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