In a data transmission system, for communicating messages between a base station and a plurality of mobile stations, each mobile station includes a radio frequency transceiver and a programmable data terminal for sending and receiving predeterminedly formatted digitally encoded messages. A keyboard subsystem...http://www.google.de/patents/US4354252?utm_source=gb-gplus-sharePatent US4354252 - Programmable digital data terminal for mobile radio transceivers
