The Level 2 Select function of the keyboard gives users access to the uppercase versions of the alphabetic characters and to special characters. On some keyboards, this function is used to access the numeric digits.
Using a keyboard with 48 graphic keys, many countries find the 96 graphic characters that can be accessed via level 1 and level 2 of the keyboard are not enough. In this situation a third level, accessed by the Level 3 Select function, can be defined to access additional characters.
The three levels are sometimes known as the Unshift, Shift, and Alt modes of the keyboard and together make up a group or layer. Several groups are needed for the keyboard to provide access to a set of characters too large to fit onto a single group. Each group may contain characters from a different character set, special characters, or accented characters. The product and its user can switch among the groups to access different sets of characters.
Support at least two graphic groups of three levels each in the keyboard logic design.
A group-switching mechanism is essential for convenient use of a single keyboard to support different scripts.
Example: Greek is one of the many scripts that do not use the Latin-based alphabets. Keyboards that support Greek are also able to support the basic Latin alphabets. A keyboard with only 48 keys supports a Greek group and a Latin group. An English-language inventory system could force the keyboard into the Latin group upon initiation.
Example: Japanese keyboards have a kana group and an English group, Arabic keyboards have an Arabic group and an English group, and USA APL keyboards have an English group and an APL group.
Example: IBM Hebrew keyboards have two groups, with English on the second group. The English group is accessed by pressing the Alt and the left Shift keys. It is possible to fit both English and Hebrew into one group consisting of three levels. If lowercase English characters are on the first level, uppercase English characters on the second level, and Hebrew characters on the third level, the user must use the Level 3 Select function for every character to enter Hebrew text. This arrangement is not a practical solution.