GB1486772A - Television systems - Google Patents

Abstract

1486772 Television; cathode-ray tube circuits INDEPENDENT BROADCASTING AUTHORITY 29 July 1974 [30 July 1973] 36206/73 Headings H4F and H4T Apparatus associated with a television receiver 11 for displaying, on the receiver screen, instead of, or additional to, the television picture, matrix or alphanumeric characters transmitted, in coded form, during one or two line periods in each field blanking period of a television signal, includes in a text signal generator a store (Fig. 3, not shown) which stores, under the control of a data receiver, a selected part of the received information which is then repeatedly read from the store and supplied to a character generator which produces signals to reproduce matrix or alphanumeric characters in a 7 Î 5 matrix which are fed to a video switch 3 and a text adder, whose output is connected to another input of video switch 3. Selection of input 1 to video switch 3 causes a conventional television display, selection of input 3 causes a display of only the matrix of alphanumeric characters; selection of input 2 causes display of both the television picture and the characters, whereas selection of both inputs 1 and 3 causes the display of both the television picture and the characters depending on which signal is instantaneously greater. The display may be in blaok-and-white or colour. The received signals may be as described in Specification 1,486,771 in which each "1" bit is represented by "10" and each "0" bit is represented by "01", each line period including a run-in, synchronizing, signal, a start code, and address signals, followed by the codes for 10 alphanumeric symbols. The transmitted data may represent 50 "pages", the information relating to only one page being stored in the store in the text signal generator. The data receiver includes two data registers, which store respectively the first and second digits of each "10" and "01" code; if the contents of the registers for any alphanumeric character are not complementary a blank is displayed. The apparatus may receive from, and return to, the television receiver 11 a modulated or demodulated signal. A second television demodulator may be ineluded so that characters received on one television channel may be displayed on the television picture received on a different television channel; alternatively the characters may be received independently of any video signal, for example over a cable network. The character signals generated in the character generator in a 7 x 5 matrix form may have added to them rounding bit signals in a 6 x 4 matrix form, superimposed in a staggered arrangement, Fig. 5A. The character signals and rounding bit signals may be derived from respective read only memories addressed in an out of step fashion.