Circuit for selecting and locking in operation function circuitry

Abstract

The present invention is circuitry which is employed with a data terminal which data terminal in turn is part of a system including a main data processor. The present circuitry includes a microprocessor which is connected to the main data processor and to the keyboard. The microprocessor processes signals from both the main data processor and the keyboard. The system has a plurality of operational function circuits, such as a circuit to effect smooth scrolling on a data display means. There is logic circuitry connected between the microprocessor and the operational function circuits. The logic circuitry provides a first path which permits signals, generated in response to instructions from the main data processor, to pass therethrough to select one of the operational function circuits and simultaneously therewith to turn the selected circuit either on or off. The logic circuitry also provides a second path which permits signals, generated in response to instructions from the keyboard to pass therethrough to select one of the operational function circuits and turn circuit either on or off. A circuit to generate an impeding signal is also included and is activated by signals from the microprocessor in response to signals from the keyboard. This last mentioned generator circuit is connected to impede signals which would otherwise be transmitted along said first path, whereby said keyboard, after selecting a particular operational function circuit, can 'lock in' that circuit so that the main data processor cannot turn that selected circuit off.