Editing Telepen

{{Short description|Barcode symbology}}
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[[Image:Telepen barcode.png|thumb|right|"''Wikipedia''" encoded in a Telepen barcode.]]

'''Telepen''' is a name of the [[barcode]] symbology designed to encode all 128 [[ASCII]] characters without using shift characters for code switching, and only using two different widths for both bars and spaces.<ref>Bushnell Associates and American Gas Association. 1989. The Bar Code Book: Introduction to Barcode Technology for the Gas Industry: System Planning Applications and Resources. American Gas Association. (Microfilm Series) Page 37 (39 in file)</ref> (Unlike [[Code 128]], which uses shifts and four different element widths<ref>{{cite web|title=Telepen Barcode Symbology|url=http://www.telepen.co.uk/telepen_symbology.htm|publisher=Telepen (telepen.co.uk)|accessdate=27 January 2013}}</ref>). The symbology was devised by George Sims of SB Electronic Systems Ltd.<ref name="Seagull">{{cite web |title=Telepen |url=https://barcodeguide.seagullscientific.com/Content/Symbologies/Telepen.htm |website=Seagull Scientific Barcode Guide |access-date=13 August 2022}}</ref><ref name="Advanova-history">{{cite web |title=Telepen: Barcode Symbology information and History |url=https://advanova.co.uk/wp-content/uploads/2022/05/Barcode-Symbology-information-and-History.pdf |publisher=Advanova |access-date=13 August 2022}}</ref> Telepen was originally designed in the UK in 1972.

Unlike most linear barcodes, Telepen does not define independent encodings for each character, but instead operates on a stream of bits. It is able to represent any bit stream containing an even number of 0 bits, and is applied to ASCII bytes with [[even parity]], which satisfies that rule. Bytes are encoded in [[little-endian]] bit order.

The string of bits is divided into single 1 bits and blocks of the form 01<sup>*</sup>0. That is, blocks beginning and ending with a 0 bit, with any number of 1 bits in between.

These are then encoded as follows:
 
* "1" is encoded as a narrow bar-narrow space
* "00" is encoded as a wide bar-narrow space
* "010" is encoded as wide bar-wide space
* Otherwise, the leading "01" and trailing "10" are both encoded as narrow bar-wide space, with additional 1 bit in between coded as described above.

Wide elements are 3 times the width of narrow elements, so every bit occupies 2 narrow elements of space.

Barcodes always start with ASCII [[underscore|_ (underscore)]]. This has a code of 0x5F, so the (lsbit-first) bit stream is 11111010. Thus, it is represented as 5 narrow bar/narrow space pairs, followed by a wide bar/wide space.

Barcodes always end with ASCII z. This has (including parity) a code of 0xFA, so the (lsbit-first) bit stream is 01011111. This is encoded as a wide bar/wide space, followed by 5 narrow bar/narrow space pairs. Each end of the bar code consists of repeated narrow elements terminated by a pair of wide elements, but the start has a wide bar first, while the end terminates with a wide space.

In addition to per-character parity bits, a Telepen symbol includes an overall modulo-127 checksum.

==References==
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{{Barcodes}}

[[Category:Barcodes]]