Abstract: An alphanumeric entry system which is provided with an electronic lock-out feature. The keypad entry system of the present invention comprises an alphanumeric keypad having function keys and display, a microprocessor, and an electronically programmable read-only memory device. The display consists of a series of system related menus as well as an alphanumeric display area. One of the system related menus corresponds to a locking feature, which may be activated by a general purpose function key. In the locking mode, the radio keypad toggles between a locked and unlocked condition as controlled by the function keys in accordance with a predefined sequence. The alphanumeric entry system of the present invention is particularly advantageous for use with portable two-way communications equipment which operate in a plurality of radio systems.

Abstract: An optimized method of bus contention comprising monitoring the bus for an idle or busy bus condition and either attempting an asynchronous bus access if the bus is idle or synchronously attempting a prioritized retry after a busy bus condition is sensed, after a bus access collision is sensed, and upon initial power-up, synchronized to the current message completion. The prioritization comprises a constant time delay plus a bit-time delay proportional to said accessing device's address identification.