Table 1.1. Plessey Barcode Format
| start character | Any number of labels/characters/digits | Checksum / check digit / code | A stop / termination character / block / pitch bar | the reverse start code |
|---|---|---|---|---|
| 4it =1101 | XXX...(eg, 012345...) | 8bit(eg. 0110 0111) | 1bit=X(eg, 1) | 4bit=0011 |
In which:
- the forward start code
The forward start code is "1101". It defines the beginning of the encoded text.
- the label / data digits
The characters of the text to encode are hexadecimal values encoded as reversed BCD.
Table 1.2. Plessey Bits Encoding Rule
Value Encoding Value Encoding Value Encoding Value Encoding 0 0000 4 0010 8 0001 C 0011 1 1000 5 1010 9 1001 D 1011 2 0100 6 0110 A 0101 E 0111 3 1100 7 1110 B 1101 F 1111 - the check code, for error detection
The check code for error detection and correction is as CRC, using polynomial division.
Is uses 2 characters, or 8 bits.
The generator polynomial is g(x) = x8 + x7 + x6 + x5 + x3 + 1 with n=8, in binary "111101001".
- the termination bar
The termination bar follows the CRC. It's a full pitch bar.
- the reverse start code
The reverse start code, with the forward start code, are used to detect the direction of reading : from left to right or right to left.
It's encoded as a reversed "0011".
Reversed because the "0" is represented by a wide space and simple bar, and "1" as a simple space and wide bar.
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| 1.2.2. How to represent bits/digits/characters |  | 1.3. Prons-and-Cons |
