Eine Architektur zur kontextsensitiven Dienstvermittlung auf Routingebene.

A portable calculator which includes circuitry for disabling operation of the display until a predetermined sequence of digits are entered from the keyboard. The circuitry includes a plurality of latches which are set in sequence in response to application of power to the calculator. The setting of the final latch disables the display so that although the computer chip is operative and responds to entries from the keyboard, no digits are displayed. Decoder circuitry responsive to the segment outputs of the computer chip permits the plurality of latches to be sequentially reset from the computer chip when the predetermined sequence of digits are entered from the keyboard or the computer chip is commanded to perform a mathematical calculation the result of which corresponds to the predetermined sequence of digits.