Method and apparatus for displaying messages on a raster-scanned display system, e.g. a CRT screen, using a segmented memory

Abstract

Abstract 1. Method for displaying messages of the teletext type which are transmitted by a television-type signal (21) and are composed of pages displayed an the screen of a scanned-raster display device (18), on which the images corresponding to these pages are drawn by line-by-line scanning, the data representative of the elements of each page to be displayed on the screen being stored in a page memory (22) in the form of a binary code and being retrieved therefrom under the control of a time-base circuit (43) which is itself controlled by the synchronisation pulses forming part of the said television-type signal (21), the said method consisting in assigning the function of page memory to at least two zones (22) in a memory unit (19) and being characterized in that it further consists in conferring on each of the said zones a base address (AB1 , AB2 , AB3 ) and an indication of an offset obtained from a status register (39), which allows the position of the start of the image to be chosen relative to the synchronization signals of the time base, the said base address and the said indication of an offset indentifying the said zone (22) uniquely, and in that, in order to retrieve the data arranged in the locations in the said zones (22), the method consists in sending to the memory unit (19) composite addresses of the base address (AB1 , AB2 , AB3 ) of the memory zone (22) in question associated with the value of the address of a memory location from which, at a given moment, the data are to be retrieved by the said composite address for display (Figure 10).

Inventors

• 👤 Gérard Chauvel

Bibliographic Details