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The topic of seven-segment display character representations revolves around the various shapes of numerical digits, letters, and punctuation devisable on seven-segment displays. Such representation of characters is not standardized by any relevant entity (e.g. ISO, IEEE or IEC).
Contents
Digit conventions
Two basic conventions are in common use for some Hindu-Arabic numerals: display segment A is optional for digit 6, segment F for 7, and segment D for 9. Although EF could also be used to represent digit 1, this seems to be rarely done if ever.
Alphabetic letters
In addition to the ten digits, seven-segment displays can be used to show letters of the Latin, Cyrillic and Greek alphabets including punctuation, but only very few representations are unambiguous and intuitive at the same time.
Also, alphabetic letters, and many other characters, are much clearer and unambiguously shown on the currently ubiquitous and low-priced dot matrix displays as well as on fourteen-segment and sixteen-segment displays. All this obviates the need for seven-segment displays to show letters in all but the most special cases.
One such special case is the display of the letters A–F when denoting the hexadecimal values (digits) 10–15. These are needed on some scientific calculators, and are used with some testing displays on electronic equipment. Although there is no official standard, today most devices displaying hex digits use the unique forms shown to the right: uppercase A, C, E, and F, and lowercase b and d. To avoid ambiguity between the digit 6 and the letter b the digit 6 is displayed with segment A lit.
However, this modern scheme wasn't always followed in the past, and various other schemes could be found as well:
For the remainder of characters, ad hoc and corporate solutions dominate the field of using seven-segment displays to show general words and phrases. Such applications of seven-segment displays are usually not considered essential and are only used for basic notifications on consumer electronics appliances (as is the case of this article's example phrases), and as internal test messages on equipment under development.
Examples
The following phrases come from a portable media player's seven-segment display. They give a good illustration of an application where a seven-segment display may be sufficient for displaying letters, since the relevant messages are neither critical nor in any significant risk of being misunderstood, much due to the limited number and rigid domain specificity of the messages. As such, there is no direct need for a more expressive display in this case, although even a slightly wider repertoire of messages would require at least a 14-segment display or a dot matrix one.