Two-out-of-five code
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In telecommunication, a two-out-of-five code is a binary-coded decimal notation in which:
- each decimal digit is represented by a binary numeral consisting of five bits of which two are of one kind, called "ones," and three are of the other kind, called "zeros", and
- the usual weights assigned to the bit positions are 0-1-2-3-6. However, in this scheme, zero is encoded as "binary" 01100; strictly speaking the 0-1-2-3-6 previously claimed is just a mnemonic device.
The U.S. Post Office POSTNET barcode uses a two-out-of-five code printed in long bars for "ones" and short bars for "zeros" to represent the ZIP+4 code for automated mail sorting and routing equipment. The weights assigned to the bit positions are: 7-4-2-1-0 (Though in this scheme, zero is encoded as 11, or "binary" 11000).
The IBM 7070, IBM 7072, and IBM 7074 computers used a two-out-of-five code. The bit positions were numbered 0-1-2-3-4, with no associated weights. The sign of a word could be A Alphameric, - Minus, or + Plus; using only bit positions 0-3-4.
The following table represents decimal digits from 0 to 9 in various two-out-of-five code systems:
| Digit | Telecommunication 01236 | U.S. Post Office 74210 | IBM 7070, 7072, 7074 01234 |
|---|---|---|---|
| 0 | 01100 | 11000 | 01100 |
| 1 | 11000 | 00011 | 11000 |
| 2 | 10100 | 00101 | 10100 |
| 3 | 10010 | 00110 | 10010 |
| 4 | 01010 | 01001 | 01010 |
| 5 | 00110 | 01010 | 00110 |
| 6 | 10001 | 01100 | 10001 |
| 7 | 01001 | 10001 | 01001 |
| 8 | 00101 | 10010 | 00101 |
| 9 | 00011 | 10100 | 00011 |
| A | N/A | N/A | 1––10 |
| - | N/A | N/A | 1––01 |
| + | N/A | N/A | 0––11 |
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