Importance

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Abstract

A system for displaying alphanumeric and graphic information on a raster scanned display device, for example, in a teletext system, includes a memory which is updated to change the display. Dynamic changes in the displayed image are provided by assigning a base address to each of one or more zones in the memory and altering the base addresses as required under local or remote control. Alphanumeric and graphic data may be combined on a single displayed page by means of identification data associated with each row or line of data to be displayed. The required capacity of the memory associated with the display device is substantially reduced by assigning a control code to data which is to be repetitively displayed, for example, spaces at the end of a line or fields of uniform color. Selected elements are thus displayed a predetermined number of times without the need for a corresponding number of memory locations. Incoming data may be sotred in a buffer memory at a greater rate than can be processed by the present system by means of a control circuit which inhibits the inputting of data for a period of time when there is a risk of overwriting or erasure of previously stored data.

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First Claim