System for digitally transmitting and displaying texts on television screen

• US 4,213,124 A
• Filed: 09/14/1977
• Issued: 07/15/1980
• Est. Priority Date: 09/22/1976
• Status: Expired

• Current Assignee: Etablissement Public de Diffusion DIT "Telediffusion de France", Etat Francais
• Original Assignee: Etablissement Public de Diffusion DIT "Telediffusion de France", Etat Francais
• Inventors: Marti, Bernard, Brusq, Roger, Poignet, Alain, Barda, Jean F.
• Primary Examiner(s): Curtis, Marshall M.
• Application Number:
  US05/833,157
• Time in Patent Office: 1,035 Days
• Field of Search: 340/324, 340/706, 340/711, 340/721, 340/744, 340/748, 340/750, 340/789, 340/802, 340/803, 340/804, 340/798, 340/799
• US Class Current: 341/12
• CPC Class Codes: G09G 5/026 Control of mixing and/or overlay of colours in general G09G5/022 and G09G5/024 take precedence
• CPC Class Codes: G09G 5/222 Control of the character-code memory
• CPC Class Codes: H04N 7/0255 Display systems therefor

Abstract

In the disclosed teletext system, the transmitter station broadcasts data cks data from several channels, the data packs being time multiplexed. Each data pack comprises a prefix signal for causing a teletext receiver either to accept the data packs of a selected channel or to reject data packs from other channels. In addition to the prefix, and possibly page flags followed by page numbers and row flags followed by row numbers, the sequence of eight-bit words, transmitted in a pack, may comprise escape eight-bit words which are followed by type identity eight-bit words, themselves followed by a sequence of characters to be displayed in the same type the identity of which is determined by the preceding type identity eight-bit words. Each teletext receiver comprises, a first conventional random access memory storing the coded characters, a second random access memory storing the type identity eight-bit words at the same addresses as those of the characters belonging to the sequence in the first random access memory. A read operation from the first random access memory, for display purpose, is performed at the same time as the read operation from the second random access memory. The output signals of the second memory select a character generator which includes a permanent memory which reads out the shape of those characters which read out from the first random access memory.

Claims

1. A receiver for a teletext system for digitally transmitting and displaying texts on a television screen, wherein a transmitter station broadcasts signals representing said text, said signals being in the form of data packs, sent over several channels, the data packs from different channels being randomly time multiplexed, each pack comprising a prefix signal for enabling a receiver to accept the data packs received over at least a selected channel and to reject data packs received over other channels, each of said data packs including the transmission in sequence of eight-bit words comprising, in addition to said prefix, page flags followed by page numbers and row flags followed by row numbers, escape eight-bit words followed by type identity eight-bit words, type identity eight-bit words, followed by a sequence of coded words identifying characters which are to be displayed in the same type which is identified by the identity words as determined by the preceding type identity words, said words receiver comprising first random access memory means for storing the coded character words at certain addresses, second random access memory means for storing the type identity words at the same certain addresses as the addresses of corresponding character words stored in the first random access memory, means for reading the words stored in the first random access memory means and at the same time as the read out if the words stored in the second random access memory, thereby simultaneously selecting a character and a type identity, and permanent memory means responsive to the read out of said second random access memory means for giving the shape of the characters read out from the first random access memory.

2. A teletext receiver for the system according to claim 5, and means responsive to output signals from the second random access memory means for controlling the luminance or chrominance in the display tube where the characters are displayed on the television tube.

4. A teletext receiver for the system according to claim 2 wherein the type identity eight-bit words following an escape eight-bit word comprises an identity component eight-bit word followed by an escape eight-bit word per character identity component, except for the last identity component eight-bit word that is directly followed by the first character eight-bit word of a sequence of characters to which the type is assigned, and buffer memory means, switching means for applying the received data escape eight-bit words followed by type identity eight-bit words serially to said buffer memory means and character eight-bit words or escape eight-bit words not followed by type identity eight-bit words to the input of the first random access memory means, said buffer memory means output being connected to said second random access memory means input and delivering its contents, except for escape eight-bit words, to said second random access memory means each time a character belonging to said sequence is written into the first random access memory means, the contents of the buffer memoring means being erased when the next escape eight-bit word followed by a type or type component identity eight-bit word is received.

3. A teletext receiver for the system according to claim 5, wherein the type identity eight-bit words following an escape eight-bit word comprise an identity component eight-bit word followed by an escape eight-bit word per character identity component, except for the last identity component eight-bit word that is directly followed by the first character eight-bit word of a sequence of characters to which the type is assigned and buffer memory means, switching circuit means for applying the received data to deliver the escape eight-bit words followed by type identity eight-bit words serially to said buffer memory means, said switching circuit means also delivering character eight-bit words or escape eight-bit words not followed by type identity eight-bit words to the input of the first random access memory means, the buffer memory means output being connected to said second random access memory input for delivering its contents, except for the escape eight-bit words, to said second random access memory means each time a character belonging to said sequence is written into the first random access memory means, the contents of the buffer memory means being erased when the next escape eight-bit word followed by a type identity or type component identity eight-bit word is received.