Method and apparatus for alphanumeric data entry

The present invention relates to a user input device for entering alphanumeric data on a device having relatively few data entry keys, and more particularly to a keypad for entering alphanumeric data on a portable communication unit. On a communication device, letters A to Z are assigned to data entry keys of a data entry keypad (), and the letters assigned to each of the data entry keys are advantageously arranged in accordance with the frequency of occurrence of the letters in use. Numeric digits are assigned to the data entry keys in the conventional way. A controller () detects activation of each data entry key on the keypad () by a user, and also detects the number of times the data entry key is activated. The controller () then accesses a key map () in memory to determine the letter or numeric digit selected by the user. From the assignment of the letters to the data entry keys and the corresponding mapping () in the memory, the letters having a higher probability of occurrence are selected by a single activation of the data entry keys and, letters with a lower probability of occurrence are selected by activating the data entry keys two or more times. The standard correspondence between numeric keys and letters of the alphabet is maintained for compatibility when entering mnemonic phone numbers and generating DTMF signals.