CA1189612A - System for digital transmission and display of texts on a television set screen - Google Patents

Abstract

SYSTEM FOR DIGITAL TRANSMISSION AND DISPLAY
OF TEXTS ON A TELEVISION SET SCREEN
ABSTRACT OF THE DISCLOSURE
A system for digitally transmitting and displaying texts on a television screen, wherein the transmitter station broadcasts, particularly in the form of data packs, data from several channels, the data packs from different channels being possibly time multiplexed, each pack comprising a prefix signal allowing a receiver to accept the data packs of a channel and to reject data packs, the set of the data packs of a channel constituting a magazine made of several pages, wherein the data packs belonging to a page are transmitted not multiplexed with data packs of another page of the same magazine, data belonging to a page beginning with a page flag followed by data indicating the page number, and ending with the next page flag, the system receiver comprising a keyboard making it possible to dial the number of the wished page, a circuit for recognizing the page flags which energized a comparator circuit comparing the data that immediately follow any page flag with the number dialled on the keyboard, data being, when the comparison is positive, sent to a memory that stores the character data, a character generator being capable to display on the screen of a television receiver tube the characters from data read out from said memory.

Description

The pre~ent invention relates to a system for digitally transmitting and di~playin~ selected item~ of data on a tele~ision receiver scraen. In short, such a system wlll be called a "teletext" system i~ the follouing.
~lore particularly, $he invention relates to a teletext system receiver~
The growing importance of information commu~icatio~
; has resulted in the building of data banks in such a manner that &uch data banks are usable in developing'infor~ation processing technics and audiovisual me~. Updating files whereîn data are stored makes those systems efficient, but the cost of the information supports presently limit~ th~
pre6~nt field of utllization thereof. A telete~t systeM
makes it possible ~o broadca~t those data from central processing stations wherei~ data issue is also made. Such a centr~lized struct~re i5 slmilar to that of ne~spaper structures a~d radio b oadcastin~ is close to nawspaper and pcriodical di~tribution.
In fact a t21etext system involve~ several asp~cts, its main goal ,being to achieve the broadest possible broadcasri~ of stored data through R~ channel~. A$ the reception end9 the major mean~ is the television receiver display screen. It displa~s pages of a text or graphics ~hich ~re tr~ns~itted i~ a~ encoded form as for example desc~ibed in the United States Patent 4,05~,830 filed ~Jv~,L~L 15, 1977 and invented by Yves Maurice Guinet and Yves ~aurice Noirel.

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~lk ~9~i~2 But a teletext service may also be transmitted through the public or a private telephone networlc throu~
whic~ a teletext subscriber calls a data bank comprising a memory serving as a file for information arrarlged in pages.
By means of a key board used by the subscriber to sele~t a page~ the subscriber can answer que~tions fro~ the filc processing unit and the pages he dcsires are s~nt to him.
In televi.~ion broadcasting5 th0 waiting time for a desiredpage ~epends on the transmission capacity which the telete~t system disposes of as well as the number of pages in the file or ~agazine~ The tra~smission capacity may con~iderably vary according as a full televlsion channel is allohed to the teletext system or only some blank lines.
~y ~ay of ~n e~a~ple, ulth a magazine containing about fifty pages and a transmission capacity of ona line p~r frame9 the ~ean waiting time is of about flfteen seconds In the case of a transmission through atelephone net~or~9 the central unit answers very rapidly, but the data tra~smission is performed at a low rat~ due tv the narrow frequency band ~idth available and may have a duration of several tens of seconds.
lY~ate~er is the utilized transmi~sion ~edium, a teletext system first implies the selection of a page of info matio~ among a plu~dlity of avallable pages~ the transmi.ssion of the selected page or pag~s, and, finallyy the displ~y Or the selected page on a television screen.
On that screen, the picture~ constituted by the written page or the grap~ics h~ve no half-tints. Theutillzation of a televisio~ receiver that can in addition receive standardized television progranls imposes certain con~traints resulting from tha television tube resolution, i.e, about 25 rows of 40 characters eachp but o~ the contrary makes possible in u~ing a set of 8 colors~ for instance, to obtain very cl~ar page setti.ng. The used alphabets depend on how character~ are written in the cou~try wherein the teletext system is utili~ed. In ~rance a proposed sy~tem co~prises a Lati~ alpnabet o~ 126 ~igns which permit~ t~ ex~end the system to the most of the languages utili~ing a Latin alphabet.
By way of example of a tele$ext system~ reference may be made to the technical article entitled "Broa~cast data i~ television" by A~ Jo Biggs and B.S. Barnaby published i~ the English technic~l review "GEC Journal of Science ~nd Technology", vol. 41, No. 4, p.117-1~4, 1974, and te t~e British Patent 1,467,240. Reference may also be made to the technical arti~le entitled "~NTIOPETMservice de télétexte"
by B. Marti a~d ~, Mauduit, publ~shed in the ~rench technical review ~radiodif~usion telévision", 9th year1 No, 409 November-December 1975, 5/5, p.18-23~ In the last mentioned article~ the features of the previously described system are indicated, ~urtherrnore in the ~escribed service pa~e~
are assembled in various m~gazine~ each magazine being Tr~ - Trade r~rk cyclically broadcast in full. Each page is identi~ied by its page number. Some o~ -those pages contain sumMarl~s and appear to help the selectlon o~ the desired page by means of a keyboard. AMong the special functions that a teletext systeln may fulfill, one would cite the insortion of a te~t in a television picture under the forrn of a caption in a language selected by -the television subscri.ber. Such captions may either be rigidly associated to tne picture or relate to short news regarding a predetermined subject matter;
they may ba written in a rectangular box cut-out of a current picture or dispenser at subscriberls will. ~eatures of this type are obviously also of interest for educational progra~ls .
According to a feature of ~h~s invention, thers is p~ovided a sy~tem for digitally transmitting and displaying texts on a tele~ision screen,~ wherein the transmitter sta~on broadcasts, particularly in the for~ of data packs, data from saveral channels~ the data packs from different channels being possibly time mult-plexed~ each pac~ comprising a preflx signal allowing a receiver to accept the data packs of a channel and to reject other data packs, the set of the data packs of a channel constituting a magazine made of se~eral pagest ~herein the data pacXs belonging to a page are transmitted not multiple~ed with data pacXs of another page of the same

2~ magazine, data belonging to a page beginning with a page 1~ 2 flag followed by data indicatin~ the pag9 number, and ending with the next page flag9 the system receiver comprising a keyboard making it pos~ible to indicate the number of the desired page~ a circuit for recognizing the page Pl~gs which energi2ed a comparator circuit cornparing the data that im~ediately follow any page flag ~ith the number indicated on the keyboard, data being, ~hen the compari~on i5 positive~
~ent to a memory that stores the character ~ata, a character generator being capable of di~playing on the screen of a tçlevision receiver tube~ the characters from data read out from the said memory.
According to ~nother feature of this invention~ there is provided a telete~t syste~ wherein the data b~longing to sach page are grouped in rows (or page lines), the data belonging to each row bein~ preceded by a row flag followed by a row ~umber, and ending with the ne~t ~ow flag, thP row number detected after e~ch row flag determining the address at which the row dat~ must be stored in the said memory.
According to anoth~r feature~ fro~ the character data the character ~enerator deliver~ to a matching circuit the character l-l~;n~nce signals, and in addi~ion logic pulses each concerning the presence or the absence of a basic color R (red) 9 Y (green~ or B (blue)~ the sa~d matching circuit transferring the luminance signal to conventional circuits f the television receiver, the said matching circuit comprising ~ ~ ~9~

associated with each basic color logic input a first diode whose anode is connected to the input of an analog amplifler ~hose output is con~ectad to the correspQnding chrominance ~elevision tube input, the anode of the first dlode being, in addition9 connected to the anodes of a s~co~d and a third diode, the first ~lode cathode being connected from the associat~d color in~ut and the output of a first voltage ~enerator delivering a volta~e v2~ the second diode ca*hode being connected frorn the output of a second voltage generator deli~eri~ a voltage vl, and the third diode ca~hode belng connected from the o~tput of a third Yoltage generator:delivering a voltage v3~ the third generator outp~t b~ing in addition connected to the output of a gate whose output is not grounded when the thre~ color inpu~s together receive logic pulse~ and grounded in any other casej with ~3~ Y2 ~ Vl 7 the value~ of vl, v2 and v3 being selected appropriately.
This înv~ntion also r~lates to an arrange~nt of the transmitted signals and means provided în each system . 20 data receiver,for m~ki n~ it possible to vary the appearance of texts displayed on a television screen so as *o break off the monotony of the current display appearancesO For in~tance, those varlations may affect the cnaracter color, background color, flashing on and off for certain characters9 changes 2~ in character height an~/or wid'h, etc~

It is to be remembered that a character generator for displaying characters on a television receiver cathode ray tube screen comprise3 a permanent memory as~ociated to ~ ra~dom access ~lemory. The permane~t mernory stores the shape information ~or every character which can be displayed. '~he random acces6 memory stores the character codes~ including the spacings or blank~ between worde forming the text to be displayed. In the random access memory the character codes are stored at addres3es which correspond to ~he geographic positions of the associ~ted characters ' in the page to be displayed. The display operation consists ~n a sequential read-out of the ro~s of character codes from the random access memory, each read operation for ~ character ca~sing in a known manner the scAnning read-out of the character shape of the character corresponding to the read character code, from the permanent memoryu Should a character occupy ten television scanning lines, each read operation for a row of character codes from the random access memory results in ten s~ccessive sc~n;ngs of the character shapes frol~ the permanent memo,~ry. Obviously sC~nn;ngs are controlled by clocks which are controlled from the display tube line synchronization. The signals resulting from the scanning o~ the shape of a character ar2 parallel delivered~ then ' convert~d into serial mode th-ou~h a sni~t register wherein the shift signal freouency is controlled ~y a clock that is controlled frorn the display tube line sync. The output o* the shi~t register is sampled at another :~requency controlled by anothe~ clock and the shi~t register output signal is transmitted toward the tube as a luminance signal.
Furthermore in charac~er transmission sy~tems wherein each character is represented by an octet, i.e. an eight-bit word, the so-caLled ~SCII code is currently in use.
Among the eight bits ol a word, one bit is normally assigned to parity check. The 7 other bits provide 12~ character possibilities Among those 128 possibilities some are assigned to character codes and other ones to function codes.
In addition, a so-called escape eight-bit word makes it possibls in practice to double those possibilities in currently changing the ~eaning of codes follo~ing an escape word.
15 - ~nother purpose of the present invention is to provide a te?ete~t system wherein the displayed characters may be of va~ious types that are dlfferent each from the other in the shape, color, si2e, bac~ground, and so on, each t~pe of displayea character being identified by means of one or several ei~lt-blt words corresponding to the character type identlty.
According to another fea~ure of the present invention9 there is provided a system for digitally trans~itting and displayi~ tex~s on a television screen wherein the sequence f the trarsmitted eight - bit words co~prises (in addition to _ g _ prefixes, pa~e flags followed by pa~e numbers~ and row flags poss.ibly followed by row numbers) e~c~pe ~ight-bit words followed by type identity eight bit words~ themselves followed by a sequence of characters to ~e displayed in the same type the identity of which is detern~ined by the precedin~ type identity eight-bit words9 each system receiver cornprisin~, in addition to ~ first conventional random m~mory access/storing the coded ch~racters, a second random ~cce6s memory storing the type identity eight~bit words at the same 2ddresses as the addresses of the characters belonging to the said se~uence in the first random access memory9 read operation from the first random access memory f~r display purpo~e being parformed as the same time as read operation from the ~aco~d random access memory whos~ output signal selects a character generator permanent memory from which the ~hape of characters read out from the first ra~dom access memory is to be read out, and/or controls the l~l~;nAnce and/or chrominance in the display tube at the time the characters are displayed~on the television tube.
According to another feature o~ this invention~ the type identity eight-bit words f~llowing an escape eight-bit word comprise an identity component eight-bit word followed by an escape eight-bit word per ch~racter identity component~ save ~he last identity compo~ent eight-bi+
word that is directly follo~ed by the f~rst character eight-_ 10 -01 bit word of a sequence of characters which the type is assigned 02 to, the received data being applied to a switching circuit 03 delivering, on the one hand, the escape eight-bit words followed 04 by type identity eight-bit words serially to a buffer memory and, 05 on the other hand, character eight-bit words or escape eight-bit 06 words not followed by type identity eight-bit words to the input 07 of the first random access memory, buffer memory output being 08 connected to second random access memory input and deliverying 09 its contents save escape eight-bit words, to said second random access memory each time a character belonging to said sequence is 11 written into the first random access memory, the contents of the 12 buffer memory being erased when receiving a next escape eight-bit 13 word followed by a type identity or type component identity 14 eight-bit word.
More particularly, the invention is a teletext system 16 for digitally transmitting and displaying text material from any 17 of many different services on a television screen. The digital 18 transmission is in the form of data packs randomly intermixed 19 from several channels, whereby successive data packs may relate to any of the completely different services. ~ach of the packs 21 have signals constituting a mazagine of several pages, wherein 22 the data belonging to each page are grouped in rows (or page 23 lines), the data belonging to each row being preceded by a row 24 flag followed by a row number, and ending with the next row flag~ The row number detected after each row flag determines the 26 address at which the row data must be stored in the memory. The 27 data for each page of information begins with a page flag. The 28 system is comprised of keyboard apparatus for identifying a 29 desired page~ whereby signals from the keyboard select between i, .~

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01 different services. A comparator circuit is responsive to page 02 flags and detects the desired page responsive to operation of the 03 keyboard apparatus. A memory responsive to the comparator 04 apparatus stores data relative to the desired page. A character 05 generator displays the desired page on a television screen 06 responsive to the data stored in the memory apparatus.
07 The invention is also a receiver or a teletext system 08 for digitally transmitting and displaying texts on a television 09 screen, wherein a transmitter station broadcasts signals represen-ting the text. The signals are in the form of data 11 packs, sent over several channels. The data packs from different 12 channels are randomly time multiplexed. Each of the data packs 13 include the transmission in sequence of eight-bit words 14 comprising page flags followed by page numbers and row flags followed by row numbers, escape eight-bi~ words followed by type 16 identity eight-bit words, type identity eight-bit words, followed 17 by a sequence of coded words identifying characters which are to 18 be displayed in the same type which is identified by the identity 19 words determined by the preceding type identity words. The words receiver is comprised of a first random access memory for storing 21 the coded character words at certain addresses, and second random 22 access memory for storing the type identity words at the same 23 certain addresses as the addresses of corresponding character 24 words stored in the first random access memory. Apparatus is included for reading the words stored in the first random access 26 memory and at the same time as the read out of the words stored 27 in the second random access memory, Accordingly a character and 28 at type identity are simultaneously selected. Permanent memory 29 - lla -6~LZ

01 apparatus is responsive to the read out of the second random 02 access memory Eor giving the shape of the characters read ou-t 03 from the first random accessory memory.
04 The invention is also a teletext system wherein the 05 display characters may be oE various types that are different 06 from each other as in the shape, color, size, and background, 07 each type of character displayed being identified by at least one 08 eight-bit word corresponding to the character type followed by an 09 escape eight-bit word. Each system receiver includes a first random access memory for storing encoded information characters, 11 second random access memory for storing the type identi-ty 12 eight-bit words at the same addresses as the addresses of the 13 information characters, and apparatus for simultaneously reading 14 the first and second access memory for a display at the same time of the encoded information characters with a selected type of 16 character shape, and a buffer memory. Switching apparatus 17 serially applies the received data escape eight-bit words 18 followed by type identity eight-bit words to the buffer memory 19 and character eight-bit words Gr escape eight-bit words not followed by type identity eight-bit words to the input of the 21 first random acccess memory. The buffer memory output is 22 connected to the second random access memory input and delivers 23 its contents, except for escape eight-bit words, to the second 24 random access memory each time a character belonging to the sequence is written into the first random access memory. The 26 contents of the buffer memory is erased when the next escape 27 eight-bit word is followed by a type or type component identity 28 eight-bit word is received.
29 - llb -01 The above mentioned features of the present invention, 02 a~ well as other features thereof will appear more clearly in the 03 following description of an embodiment, the said description 04 being made in conjunctin with accompanying drawings, wherein:
~05 Fig. 1 is a block diagram of a teletext transmitter ~06 according to this invention, 07 Fig. 2 is a block diagram of a teletext receiver 08 according to this invention, 09 Fig. 3 is a schematic diagram of a matching circuit for ~6 29 - llc -z 01 matching the voltage/light characteristics utilized in the 02 receiver shown in Fig. 2, 03 Fig. 4 illustrates waveforms of signals used in the 04 matching circuit shown in Fig. 3, 05 Fig. 5 is a block diagram of memory circuits and 06 character generator usable according to this invention in ~he 07 teletext receiver shown in Fig. 2, and 08 Fig. 6 is a schematic diagram of a mixer circuit 09 utili~ed in the receiver shown in Fig. 5.
The assembly shown in Fig. 1 is similar to that shown 11 in Fig. 1 o the description of the already mentioned U.S.
12 Patent 4,058,830. To a modulator circuit 1 and a transmission 13 antenna 2 there are switchably connected a number of data 14 sources, such as the data source shown which comprises a data processing circuit 3, connected to a number of control sets 16 4.1-4.n. Data procèssing circuit 3 includes a shaping circuit 17 5, and a memory 6 whose input is connected to the output of 18 circuit 5 and whose broadcast output may selectively be 19 connected to modulator circuitry 1 while its control output is connected to the input of a conversion circuit 7. Each control 21 set 4.1-4.n includes, as shown at 4.1, a moni-tor screen 8 and a 22 composing typewriter 9. Each typewriter 9 has a data output 23 connected to the input of the circuit 5 and a data input 24 connected to the output of the circuit 7.

``l?

01 Each control set 4.1-4~n allows a journalist or other 02 operator to compose pages by means of the typewri~er 9 while 03 checking on the monitor screen 8 every characteristic of the 04 Einal color picture, e.g. the character size, flashings on and 05 off and graphic particularities. Each typewriter 9 is similar 06 to a typing machine and includes logic circuitry for composing 07 and updating the documents. Output data from sets 4.1-4.n are 08 put, in accordance with given standards, in circuit 5, then 09 stored in the memory 6. Memory 6 may be a disk memory wherein there are stored the sequences of codes to be transmitted ll corresponding to the language determined in the abov~-mentioned 12 French technical article. Thus memory 6 constitutes a file of 13 pages that are periodically read out and ~ransmitted to the 14 modulator circuitry l to be broadcast. An operator controlling a set 4.1-4.n can also have displayed on his control screen 8 a 16 selected page read out from memory 6 through circuit 7.
17 Embodiments of the equipment shown in Fig. l are 18 known. They can either be embodied in a wired logic form or in l9 a programmed form controlled frcm a computer.
The assumption may be made that, as in the already 21 mentioned U.S. Patent No. 4,058,830, a data broadcast is 22 made on a television channel in the idle lines of the 23 television picture. rrhose data are assembled in data packs 24 including up to 32 eight-bit words or octets. To each data ..~.. ~

01 pack -there is assigned a prefix indicating the data source 02 address and the number of words contained in the concerned data 03 pack. When the length of data to be transmitted compri es more 04 than 32 eight-bit words, it is shared among several data packs 05 and the prefix contains the pack number in addition to other 06 information. Within the prefix also included are 2 eight-bit 07 words for synchronizing the receiver terminal local oscillator 08 and another eight-bit word for synchronizing the said eight-bit 09 words in each data pack. Thus a full transmitted data pack includes 40 8-bit words wherein each of the 320 bits represents 11 a black when the bit value is 0 and white when it is 1.
12 Possible interferences between these digital signals and the 13 proper video signal is reduced by selecting a repetition 14 frequency that is an odd multiple of the line frequency. There are 397 periods in a line which results in a bit frequency of 16 6.20 MHz, with a non-return-to-zero modulation.
17 As described in the already mentioned U.S. Patent 18 No. 4,058,830, a computer used as an electronic control unit 19 knows the list of the idle lines in a picture signal and inserts into those lines the data packs it receives from the 21 various telete~t editors, similar to that shown in Fig. 1.
22 Connections from the various memories 6 and modulator 23 circuitry 1 are preferably constituted of links, such as 24 the link described in the French paten-~ 2,268,308 !7 ~s~

entitled ~Standardized colllrnunication interface device~'.
Such a link makes it possible to slow down the data flow of a data source consti~uted by a data memory, when the broadcast system is blocked. When using a broadcasting ~etwork, it is not possible ~o control directly the output data flow from a source deri~ed from the receiver input capacity; to overcome this lack o~ feedback control~ a ~imulated receiverS similar to ~he slowest receiver7 is prov~ded in the cont~ol unit. When using other transrnission media the said link provide~ thc funct~ons needed for a correct trans~ission o~ the digital signals.
Reception terminal shown ln Fig. 2 is designed to supplement a conve~tional television receiv~r and is used to demodulate the data ~ignals transmitted f~om the station shown in Fig. 1, to resh&pe them~ *he~ to write them into a store sc that it is possible to restore a vlsible page on the associated television receiver screen. Reception term~al ma~ ~ a separate unit assoclated to a con~entional ~ele~ision recei~er or a portion integrated in an accordingly designed ~elev~sion recelver.
The receive terminal shown in Fig~ 2 comprises, like a conventional television receiver, a reception-demodulation clrcuit 10 delivering~ on the one hand, audio signals to a loud-speaker 11 and, on the other hand, video signals to a color decoder and scanning generator 12, Color signals B1 _ 15 _ ~9~2 01 (blue), Vl ~green) and Rl (red) as well as ll~m;n~nce signal 02 Erom the generator 12 are not transmitted, contrary -to what 03 occurs in a conven-tional television receiver, directly to tube 04 13, but through a video switch 14 that has still another 05 function as will be hereinafter described.
06 Furthermore the receive terminal shown in Fig. 1 07 comprises a circui-t 15 separating data from -the video signal, 08 the input of the circuit 15 being connected to the video output 09 of the circuit 10 and output of the circuit 15 being connected to a first selection block 16, similar to that of the terminal 11 equipment described in the already mentioned U.S. Patent 12 4,058,830. The output of block 16 is connected through an 13 above mentioned link J to a page selection block and a data 14 decoder 17, whose outpu~ is connected to the input of a page memory 18. A viewer keyboard 19 has its outputs suitably ~16 connected to control inputs of selection block 16 and decoder 17 17. The output of memory 18 is connected to the input of a 18 character generator 20. Signal outputs of character generator 1~ 20 are connected to color inputs R2 (red), V2 tgreen) and B2 (blue) of the video switch 14 as well as to a luminance input 21 thereof. A con-trol output of -the keyboard 19 is also connected 22 to a control input of the video switch 140 23 In the circuit 15, a stable oscillator, not shown, 24 generates a clock signal at 6.20 MHz, as mentioned above.

~L~L8~i1Z

01 When, after the detection of a line synchronization pulse, a '2 video signal transmi-tted froxn circuit 10 presents a sequence of ~3 alternative white and black points at that clock requency, the 04 said oscillator is phase locked with the received pulses. The 05 oscillator output is then used as a clock for the received 06 bits. Thus that oscillator is utilize~ to correctly separa-te 07 the video data signal from a current television video program 08 signal. Received bits are processed as eight-bit words in 09 circui~ 15 and service information, such as channel number and subscription period, are taken therein into account to make 11 only the desired channel or magazine valid. All the circui-try 12 performing such a process are described in the already 13 mentioned U.S. Patent 4,058,830, and particularly regarding the 14 validation of the desired channel described in Fig. 6 thereof.
Assuming the validation is positive, received bits 16 are sent to block 17 through link J. In practice, in the 17 embodiment described, a channel of a system described in the 18 already mentioned U.S. Patent No. 4,058,830 is equivalent to a 19 magazine. It is known that the various channels of such a system are time multiplexed; so it is for the various 21 magazines. As a result link J transmits the data contents 22 of a magazine serially per groups of 8-bit words, but 23 with intervals between those groups due to two ~4 - 17 -9~

reasons, the first one o~ which results from the tim~
multiplexed broadcasting mode of ~he magazlnas and the other one results from the transmission mode through link J, ~he transmi~sion thr3ugh J from 16 to 17 being only possible ~hen block 17 is ready to receive data. Thus transmission ~ink 3 i~ performed in a~ asynchronous manner.
In block 7 a flrst operation is to select the de~ired page t~rough the magazineO Indeed~ as de~cribed i~ the already mentioncd ~rench ~echnical ar~icle, a magazine is composed of ~everal pages wit~ particularly a ~irst page indicatin~ the magazine summaryO In the maga~i~e the pages are naturally ordere~ according to increasing numeral~. It is also to be noted that in the broadcast of a maga~i~e the pages thareof are not time multiplexed~ i.e. page data ara preceded by a 8-bi~ word repre~enting a page flag~
followed by the page nu~ber, and are followed by another ~-bit word representing another page flag followed ~y the next page number. As a ~esult, in block 17 there is performed the detection o~ each page flag, then eac~ time a reco~nition is posi~ive the compal~ison of the immediately following page number 8-bit word 1~ith the page number indicated by the keyboard 19. 1~nen the result of th~ comparison is negativey the already received 8-bit words and ths following ones are destroyed up to t1le dete~tion of the next page flag. When the result of the comparison is positi~e~ ~ne 8-words recei~d _ 18 -up to the detection of the next page flag are transmitted to memory 18~ after having been processed a~ ~ollows. I~
each page the char~cters are ordered in rows. In the 9equence of data 8-bit word4, each row is preceded by a row flag followed by an 8-bit word lndicating the height of the followin~ row in the pa~e. The ro~ number 8-bit ~ord is used to determine one of~ the addresses of the character~
to be sto~ed in the memory 18. The other address is determined by the posi~ion of the character 8-bit word in the ~equence of character 8-bi~ wGrds constituting a row, includin~ bla~ks between characters, It must be noted that the s~quence of 8-bit words co~stituting a row includes, in addition to the proper character words~ so.~e 8~bit words indicati~g character partic~lars, such as the color. These function 8-bit words are also stored in the memory 18 at the address of the characters they characterise.
Thus~ ~or o~t~;T~;ne the p~ge that he requires, a magazinc viewer ~irst keys the r~quired number on the keyboard 19 for consulting 'the magazine summary. From the above lt will be underslood that this results in the summary page being selected in blocl~ 17. ~hen the ~iewsr composes on keyboard 19 the numbe~ of the page he wishes to read.
It will be noted thac the data stored in the memo~y 18 provide an electronic ~eo~raphic representation of the characters in the corresponding page~ These data are read 19 _ o~ o out to the character ger1erator 20 usinO~ a ti~e basis provlded in such a rnanner as to rnake it pos~ible for the me~ory 18 to be read completely in a telaYision frame periodO
C~arac-ter generator 20 receives eacn character 8-bit word read out from the ~emory 18 and builds the corre~ponding letter shapa from a video signal havi~g two conditions9 one conditio~ being black and the othsr whi-te. In addition~
it receive~ the associated functi~n 8-bit word indicating for insta~ce the color and delivers the correspo~ding lo logic signals R2~ V2 and B2.
To make clearer how signals delivered froln generator 20 are d~splaysd on screen 13, video switch 14 ~ll now be described in detail in conjunction with ~ig~ 3. Vldeo ~witch 14 ma~es~o3sible, on the one hand~ control of the swltching o~ logic and analog signal~ to be displayed on tube screen 13~ ei~her corresponding to a text picture froin 20~ or a current televl~ion picture from 12 elther animated or not~ and, on the o~ner hand, to determine the character color selected among 8 shades, i.e. for in~tance, red~
green, blue, yello~, .~agenta, cyan~ ~hite and blackO
Video s~itch 14 a~so perPorms an adap-tation o~ the Yoltage/light characteristics of the tube to the control of the synthe~ized si~als. Such an adaptation is currently perPormed in the tran~misslon station, when broadcasting pictures, belng 'hen known as the gamma-correctionO But with synthesized plctures whe~ein signals have a logic nat~re, no gamma-correct~on can be made at ~he transmission station, Accordingly7 according to the present invention, ther~ i~ provided means for receiving the signals deli~ered from memory 18 and for adapting the corresponding voltages to suitable values needed for the control of the display tube.
For tha~ purpo~e, ~ideo switch 14, shown in Fig~ 3~
has two set~ of color signals inputs, i.e. on the one hand, R1, ~1 and B19 and, on the other handt R2, V2 an~ B2.
Furthsrmore, a l~minance input 21 is connected ~rom the associate.d output of 20 while ano~her lun~inance input 22 is connected ~rom the associated output of 120 Inputs 21 and 22 ar~ respectiv~ly conn2cted to inputs of amplifiers 23 and 24. Each amplifier 23 or 24 has a gain equal to 1 with a high input impedance and a low output in~pedance so as to be a voltage source. Signals delivered from 23 and 24 are respectivel-~ adju~ed ~y diodes 25 a~d 26 supplied by a stable voltage genera~or 27. Transfer time constants for these input signals are dete~nined by capacitors 2B and 29 according to the input impedances of the ampli~iers 30 and 31. Dep~nding on the position of a ~witch 32 co~trolled by a con~rol signal from ~he keyboard 19. via input 337 either a signal ~rom amplifier 30 or a signal from/a~plifier 31, ~especti~ely corresponding to either signal applied to 21 or signal applied , "

z to 22~ is tran~mitted~ via output 34~ to the l~ n~nce input of tube 13.
The i.nputs Bl, V1 and Rl are respectively connected to the associated i~puts of a chrominance switch 35, through amplifiers 36B~ 36~ and 36R which operate as voltage 60urces, like a~plifie~ 23 and 24. A chrominance switch 35 is also controlled by the control input 33. The inputs B29 V2 and R2 are respectively connected to the inputs of logic si~nal amplifier~ or lnverters 37~9 37V and 37R. The outputs of in~erters 37B, 37V and 37R are respectively connected, on the one hand, to the inputs of a lo~ic cper~tor 38 ~nd, on the other hand, to the inputs of logic signal amplifie~s 39B, 3~V and 39R. The output of amplifier 39B
i~ connected to the cathode of a diode 40B whose anods is connected, firs*9 to the anode of a diode 41B~ second, to the anode of a diode 42B andt ~inally, to the input of an am~lifie~ 43B, operating as a voltage ~ource, through a resistor 44B. Outputs of amplifiers 39V and 39B are also r~sp~ctively connected to similar sets of diode3 40Y9 41V
and 42V~ and 40R~ 41R and 42R. The anode of diode 40V is con~ected to the i~put of a ~oltage source ampli~ier 43V, via a resisto~ 44V, while the anode of diode 40R is con~ected to the input of a voltage source amplifier 43R, via a resistor 44R. ~urthermore the cathodcs of diodes 40B9 40V
and 40R are parallel connected from the output of an adjustable - 22 _ voltage generator 459 through adjustable re~istors 46~, 46V and 46R respectively. The cathodes of diodes 41B, ~lV and ll1R are parallel connected from the output of another adjl-stable voltage generator 47. The cathodes of diodes 42B7 42V and 42~ are paral].el connected f~om the output of a last adjustable voltage generator 48, through a ~esistor 49, on the one hand, and from the output of logic operator 38, on t~e other hand. The output~ of an)plifiers 43B, 43V and ~3R are raspectively connected~ as outputs of 36B, 36Y and 36R~ to associa~ed inputs of.s~itch 35.
Depending on the condition of the control wire 33 ~rom the keyboard t9, the switch 35 delivers ~rom outputs 503~ 50V
and 50R to the tube 13, either signals from the a~nplifiers 43, or fron~ the ampli~iers 36. Resistances 44R, 44V and 44B are ad3ustable resistors ssrvi~g to correct diode characterlstic variations.
Now with ref~rence to Fig. 4, the voltages applied to respecti~e inputs ~, B and C of the ampliflers ~3R, 4,V and 43B wil~' be considered versus logic pulses delivered from the generator 20 to the input~ ~2, V2 and B2.
~irst,Lhe assumption is made that, at ti~e tl, the generator 20 delivers three logic pulses. The logic operator 38, operating as an A~-D gate or a NOR ga~e, accordi.ng to the technology in use, tnen has its o~tput off, which allows the ~oliage generato~ 4~ to ap~ly, through the resistor 49, a turning-on voltage to the dioda~ 42R, l~2V and l~2B7 that voltage having t~e highest value, i~dicated by v3~ and being transmitted to the illputs A, B and C. Assu~ing that tha switch 35 has been correctly switched by the si~lal on inp~t 33, the three amplifiers 43R, 43V and 43B transmit those voltages v3 to tube 13 which eauses a white spot to ~ppear on the screen of tube 13.
At a time t2, ~he a~sumption i~ made tha-t only the inputs R2 and V2 receive logic pulses from the generator 20, but the in~ut B2 receives no pul~e. A3 a result thereof the output of logic operator 38 is grounded so that the diodes 42~, 42V and ~2B are off. Through th~ two legic in~erters 37B and 39B~ the zero voltage applied to the lnput B2 is delivered from amplifier 39B so that the diode 40B i~ also off while-the diode 41~ is on and transmits to the junction point C the voltage vl delivered from the amplifier 47, Pulses appliad re~pectively to inputs R2 and V2 are transmitt~d thrvu2h amplifie~ 37n and 33R9 and amplifiers 37V~a~d 39V, which tU~l diodes 40R and 40V on.
Since a volta~e of value v2 delivered from the amplifier 45 is higher than a voltage of valu~ vl delivared fro~
genara~or 47, diodes 41R and 41V are off and only voltage v2 is applied to junction points A and B~ Voltages v2 from A and ~, and voltage vl from C are tra~smitted to t~be 13 uhich dis?lays a yellow spo-t. The other t~o com~inations - 24 ~

of pulses re~ult in a cyan spot (B and G) and a magenta spot ~R and B)~ respectiv~ly.
At time ~3, the agsumption is ~ade that only the input B2 receives a logic puls~ from the generator 20.
The output of logic operator 38 is still grou~lded turning diodes 4ZR, 1~2V and 42B off~ Diodes 40Y and I~OR are off9 because the outpu~s of ampli~iers 39V and 39R are grounded so that a voltage v1 from the generator 47 is applied, via diodes 41V and 41R~ to junction points A and ~9 respectively. On the other hand, the diode 40B is on and transmits the ~oltage ~2 from the amp~ifier 45 to juncticn point C. Voltages v1 from points A and ~, and voltage - ~2 from point C are tra~s~itced to tube 13 which di~plays a blue spot.
Between ti~es t1 and t29 or betwee~ times t2 and t3, the ou$put o~ operator 3~ i~ still groundedO The diodes 40R, 40Y and 40B ar~ off, Onl~ the three dlo~es 41R9 41V
and 41B are on~ The voltage v1 is applied t~ all the junction points A, B and C. A black spot a~psars on the ~creen~
It will be understood from the above that the switch circuit 14 provides a good Lle~ibilit~ in adjusting the colors. Particularly9 white is defined by ~djusting the voltag~ v3 from the generator ~89 black is definad by a~justi~g the v~l~age ~1 from the generator 479 and the basic colors R9 G and B are defined by adjustlng the generator ~5 and the resistors 46R? 46V and ~6B~

It would obviously be possible, instead of using a ~ogic operator 38, ~o utilize -~everal such operAtors, - each being associated to an adjustable ~oltag~ ~enerator9 so as to permit the adaptation o~ the lt~min~nce o~ the variou~ shad~s according to user's wishes.
It is to be noted that the link J is preferably of the type described in French Patent No. 2~268,308. Such a link makes possible an asynchronous operatlon from selection block 1~ to decoder 170 Furthermore, as an ~lternative~ the input of the link J may be connected from a wired telete~t di~tribution network~ for instance~
utilizing the public telephone network~
In an embodiment of this in~ention which will now be described in dstail~ the mer~ory bloc~ 18 and the character generato~ 20 are designed as sho~n in ~ig, 5. In practice the memory 18 comprises two random access mem~ries (~AM) 51 and 52~ as well-a~ a switching circuit 53 and a bu~fer memory 5~. The input of the switching circuit 53 is connected, vi~ a liIle 559 from the OUtp'lt of` circui-~ 17, Fig. 2y that delivers the character 8-bit words and the row function 8-bit words. Row addressing inputs in the memories 51 and 52 are parallel connected~ via line 56, from the output of the ci~cu-it 17 which delivers the row numbers.
The switchin~ circuit 53 has an output 57 which is connected to the data input of memory 5f and an output 58 which is - 26 _ ~9~

connected to the input of the buffer memory 5~. Tha output of the buffer memory 54 is connected to the data input of the rnernory 52.
Data for application to the input o~ ~witchin~
circuit 53, via line 55, ~ay be grouped in the foll~wing families: first~ in the simplest ca9e, an alphanumeric character 8-bit ~ord, then an escape 8~bit word plus either a character 8-bit word or a conventional functlon 8-bit word, and finaily an escape 8-bit word plu5 a character type identity 8-bit word. The switching circuit 53 includes detection ~eans for reco~nizillg third family data - escape 8-bit word plus character type identity 8-bit wo~d -, t~ose ~nea~s being possibly sirnple comparators, and : m~k; ng it possible to send them to output 58 while flrst 17 and seco~d family data are sent to output 57.
By way of exam~le, some types of identity 8-bit ~ords will now be ill~strated An 8-bit word ~1 may be provided w~erein the five first bits c~rr~, when they are în the l~conditio~ the followin~ information, but, when they are in the,0-condition, no informat~on.
1st bit Znd bit 3rd bit 4th bit 5th bit 6th bit 7th bit ~ed Gre~n Blue Graphic 1 0 0 8th bit , Thus, ~ith a 8-bit word 1000100X, it indica tes that the se~uence of the characters following it must be displayed %

in red o~ the tube ~cree~. By ~ay of exa~ple~ with a 8-bit word 01 lOlOOX, it indicates that thc ~equence must be di~played in cyan. When the 5th bit i~ 1, it indicates that the 8-bit word is a word ~1; when 6th and 7th bits are 0, switching circuit 53 can detect the function 8-bit wo~ds, the meaning of the 1~th bit will be described i~ the followingt t~e 8th bit is a parity bito :i~ In a sam~ manner~ a 8-bit word F2 ~ay be provided wherein the bits have the followin~ meanings.
. 1st bit 2nd bit 3rd bit 4th bit 5th bit 6th b.it 7th bit Height W'idth Ground ~lashing 0 0 0 8th bit X
When the 1st bit is 19 it lndicates tha-t the character hei~ht ls to be doubled, whe~ the 2nd bit is 1, it indicates that th~ character width is to be doubled; when the 3rd bit is 1, it indicates that the ground onto which the character is to be displayed must ha~e its color reversed;
when th~ 4th bi~t is 1~ it indicates that th0 character must be ~lashed on and o~f~ Thus, with a 8-bit word 1 lOlOOX, it indicates that height and width of the charac ters must be doubl ad and they must be ~lashed on and off~ The 5th bit bèing 0 indicates that th2 8-bit wor~ is a word F2.
in Now it is possible to understand that, when/the sequence of` 8-bit words applied from li~ 55 to switching ~ 28 --... .. . . . . ..

circuit 539 there ~3 the following serie~: ~ F1 ~ F1 a b c . . .;
switchin~ circuit 53 will write the four word~ ~ F1 ~ ~1 into memory S4~ then words a b c ..., into ~emory 51, Writing of fir~t character word a into memory 51 which is detected in circuit 59 initiates writing at the same address into memory 52 of words ~1 and F2 from memory 54 (words 0 being not transmitted ~rom memory 51~ to memory 52~o Clrcuit 59 is connected ~y control line 60 to memory 5~
Buffer memory 54 is connected to RA~ memory 52 by line 61.
Read out from memvry 54 to memory 52 does not alter the co~tents of memory 54-. Thus~ when writing b into memory 51~ ~1 and ~2 are written at th~ sa~e addres~
a~ b into mamo~y 52. Ag a conclusion at corresponding addresses cnaracter ~ord 5 are written in'o ~2mo~y 51 and type identity words are ~ritte~ into memory 52. The contents of memory 54 are erased at the next writin~ into bu~fer memory 54 of an escape word followed by an identity word, In addit~on io function words ~1 and ~2, othar function words ~ay also b~ provided, as for instance ~3 ma~ing it possible to change from a character shape to another character ,shape, taken together the 5th and 7th bits then indicate an i.dentity word which ls detected in switching circuit 53~ the 6th bit being O and the 8th bit being ~till a parity bit.

- 29 _ The characte~ generator 20, shown in ~ig~ 5, comprises four permanent memories 62-~5; a switch 65, a mixing circuit 67 ~nd a monostable circuit 63~ Each perman~nt memory 62-65 is associated respectively wlth a shift register 69-72 designed for delivering serially the bits conventionally read in parallel ~roma character generator permanent memory. It is to be remelnb~red that the scanning of character shape is performed in memories 62-65 line per line 7 each basically corresponding to a television p~cture line. A clock 73 is also provided which con*rols read o~er~tions from memories in accordance wi~h television picture line synchronization signals. In ~i~. 5, some inputs S are also indlcated wnich mea~ that television line synchronization si~nals are also used -for rea~ing the concerned memories or controlling repetiti~e operatio~s; howeYer9 to simplify the drawing, all the ~nputs S are not indicated.
Swltch 66 is provided ~or selec~ing one of the registers 69-7~ that is to be connected to its output 74 connected to mi~ing circui-t 67; it also d0termines the read-out operation rate9 or in other words the sampll~g rate of register outputs~
The read-out output of R~ memory 51 is parallel connected to read-out address ir.puts of permanent ~emories ~5 62-65. Parallel read-out output~ of memories 62-65 are respecti~ely connected to parallel inputs of register4 69-72, The read-out output of RAM memory 52 has as ma~y wi.~es a~ significant bits i~ function word~ ~1, F2 and F3, Thus these are indicated wires R,G~ B respectively corresponding to the ~irst 3 bits o~ F1, wire ~ corresponding to the first bit of F2, wire L co~responding to the second bit of F2, wira F corre~ponding to the third bit of ~2 and ~ire C corr~sponding to the fourth bit of F2 t In addition, there is provided a line M comprislng four wires correspondi~g to the significant bits of r`3, which are in the de~c~ibed example assumed to be two bi-ts s~nce four permanent memories are provided.
~ire H ~ connected to ~ control input of the clock 73~ ~en H i8 low, the clock 73 operates at a normal rateS
i.e. for each picture line RA~I memory 51 is read as well as a character ~h~pe line in the permanent memories 62_65, that line corresponding to the address read o~t from 51.
When H is high~'the clock rate of clock 73 ~s di~ided by two. As the clock 73 designates, after counting, the address of the line to be read in the character shapes of the permanenl memories, when ~ is high~ cach character shape line i5 successlvely read twice at the picture line frequ~ncyO
Thus the height o~ ths displayed character occupies twice as mally lines on ths tube sc~en. Its heigh-t i3 doubledO

- 3~ -z ~ire L indeed lncludes t~o wires, one L1 controllin~
the bit shift rate in re~i~ters 69-72, the other L2 controlling th~ horizontal address progress rate in RAM
meMory 51, via input L2. Obviously these two rates are also related to the television picture line synchronization.
~en wire ~ i~ low, the shift rate and the sampli~lg rate are no~mal. When wire L is high~ the shift rate and the sampl~ng rate are both divided by two 60 that the same bit stays twice as long in the output cell of each shift regi~ter and th0refore can be sampled twice. Thus information relating to a c~aracter point can be sent twice to the displ~y tube in the picture line~ Accordingly the ; width is doubled. As a character then occupies a wide~
place in t~a displayed row, it i8 necessar~ throu~h input L2, to reduce by two the progress of the character word3 i~ the corre~po~dlng row in memory 510 The four wires of line M make possible the selection of the parmanent memory whose output is utilized amo~g the memorics 62_650 Indeed a~ each read-out operation ~ro~ the memory 51, the ,four memories 62_55 ars read-out in parallel~
However, the switch 66 allo~s only one co~ection with the circuit 67. With four permanent memories wherein there are respectively storad four alphabets, it appears that two bits of words ~3 permit in a simple man~er the language to be changed depending on the texts to be displaye~.

When wire C is low~ the monostable circuit 68 is at rest~ when the wir~ C is high, the monostabl~
circuit is triggered on. The monostable circui~ rate may be of about about 1 Hz and is used as described hereabove for flashing characters on and of~.
~eference will now be made to ~ig~ 6 for describing the purpose3 of wires ~, V (or G), B and ~. In ~ig. 6~
there are s~i~l shown the wire 74 connecting the output of the switch 65 to the clrcuit 67, as well as the output wire 7~ from the monostable circuit 68. First lt is to be remem~ered that the wire 74 carries digital si~nals relating to the lu~inance information. Thust with each character shape line scann; ng in a parma~ent memor~, after the parallel-serlal.conversion in the corr~sponding shift register, the ~ignal transmitted by 74 ~s shaped as indicated b~ the ~-ave form 1~ ~ig. 6. When signal 1 is hi.gh, a spot i~ lit on the tube~ when signal 1 is low, the back-ground doe~ no* light. The wire 74 i9 co~nected to the input of a switchable in~erter circuit 75 ~hose output is connected to a,s-~itch 77. ~he sig~al output of the switch 77 is connected, on the one hand, to the output 21 through a shaping c~rcui' 78 and9 on the other hand, in parallel to first lnputs of three ~D gates 73, 80 and 81. A second input of gate 79 is connected to wire R, a second input of gate ~0 is connected to wire R (or G), and a second input of gate 81 is connected to wire B. The outout of gate 7 is connac-ted to wire R2 through a shap:Lng circuit 82, the output of` the gate 80 is connected to the wire Y2 through a shaping circuit S3~ and the outpu-t of the gate ~1 is connected to -the wire B2 through a shaping circuit 8!~.
The control input of ths switchable in~er~er circuit 76 is connacted to the wire ~ while the control input of the switch 77 is co~nected to the wire 75.
Assuming that the wires ~ and 75 are at rest in the 0-condition or 1oW9 the slgnal 1 fro-m w~re 74 is applied without change to the circuit 78 and the gates 79-81.
From tha output 21 of circuit 78, the output signal is processed in tha switching circuit 14, Fig. 2, shown in detail in Fig. 3. In-addition ass~min~ that the wire R
ls (or G) îs in the 1-condition or high~ conditions 1 of signal 1 are transmitted through gate 79 and applied to shaping circuit 82 be~ore being processed in switchlng circuit 14, Fig. 2. Thu3 it appear~ tnat the red chrominanca signal is simllar to the 11l~;n~nce signal that causes the character to ba displayed in rad. Whan wiras R and Y (or G) are high, conditions 1 of 1 are transmitted and wires ~2 and V2 b~come high, the color mix belng performad in the tube after p.rocessing ln switching circuit 14~ Tha result is thus obtained tqat characters may be displayed in whi-te or as one of 3iX predatermlned colors by using the ~rs-t three bits of the word ~1.

_ 3~ _ æ

When the wi.re ~ is in the 1-condition or high, the output signal from 76 is re~ersed with respect to 1, i.e. 1. Such an outpu ~ signal is still processed in gates 79-819 as signal 1, but contrary ~o the previous described case, only the part~ outside of the characters correspo~ding to conditions 0 of 1 appear.displayed in color.
When the wire 75 is pariodically turned to the ; 1-condition, the transmission of signal 1 is interrup~ed through the clrcuit 77 during these l-conditions. As a .. . ...... . . .
~ 10 result the lllm;n~nce si~nal is accordingly interrupted : which causes the character to flash on ~d off on the display~
Tha shaping circuit 78 is also utili~ed for adding ~he digital synchronization signal to the lll~;n~nce signal~
as indicated by S.
~lso to be noted that9 with no type-identity in~ormation, the outputs ~VB of memory 52 are high or in tha l-conditlon~ so as to display white characters on a black bac~ground~
Read-out opera~ions are ob~iousl~ performed at the same time in th~e ~ 1 memories 51 and 52 so as to read characters ~rom perm~nent memories at the same time as the conditions of the output wires of memory 52 are controlled by identi~y bi~ in words F1, F2 and .~3.
With respect to the bit corresponding to a Graphic in word ~1, it must be understood that there i~ provided, - 3~ -for instance close to the per~lanent ~emory 62, a wired memory whsrein there are 9 ~ored .six-point rectangles making it possible, by di~playlng them side by side~
for graphic~ to be ~roduced on the screen. In practice, the output of the RAM rnemory ~2 has a wire corresponding to the 11th bit of F1, which permits the wired memory to be selected instead of the ~emory 62 in a similar manner to the selection controlled by the wire M, Graphic rectangle cudes are provided in the ~CSII code"
In an alternative method of operation of the teletext system ~ccording to this invention9 it is pre.erred to begin each row with a type identity word, the character type being possibly ch~nged within the row, but returning to tne initial ~pe at the end of each row, Thus the display is resy~chronized at the beg-nnin~ of each row.
t ,

Claims (8)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A teletext system for digitally transmitting and displaying text material from any of many different services on a television screen, the digital transmission being in the form of data packs randomly intermixed from several channels, whereby successive data packs may relate to any of said completely different services, each of said packs having signals constituting a magazine of several pages, wherein the data belonging to each page are grouped in rows (or page lines), the data belonging to each row being preceded by a row flag followed by a row number, and ending with the next row flag, the row number detected after each row flag determining the address at which the row data must be stored in a memory means, and wherein the data for each page of information begins with a page flag, said system comprising keyboard means for identifying a desired page, whereby signals from said keyboard select between said different services, comparator circuit means responsive to page flags for detecting said desired page responsive to operation of said keyboard means, memory means responsive to said comparator means for storing data relative to said desired page, and character generator means for displaying said desired page on a television screen responsive to the data stored in said memory means.

2. A teletext system as defined in claim 1, in which each of said data packs includes the transmission in sequence of eight-bit words comprising page flags followed by page numbers and row flags followed by row numbers, escape eight-bit words followed by type identify 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, a 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 of 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.

3. A teletext system as defined in claim 2, in which the receiver is comprised of 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 system as defined in claim 2, wherein in the receiver 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.

5. A teletext system as defined in claim 2, wherein in the receiver 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 output 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 memory means being erased when the next escape eight-bit word followed by a type or type component identity eight-bit word is received.

6. A teletext system as defined in claim 2 wherein the display characters may be of various types that are different each from the other as in the shape, color, size, and background, each type of character displayed being identified by at least one eight-bit word corresponding to the character type following an escape eight-bit word, system receivers each including a first random access memory means for storing encoded information characters, second random access memory means for storing the type identity eight-bit words at the same addresses as the addresses of the information characters, means for simultaneously reading the first and second access memory means for a display at the same time of the encoded information characters with a selected type of character shape, buffer memory means, and switching means for serially applying the received data escape eight-bit words followed by type identity eight-bit words 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 memory means being erased when the next except eight-bit word followed by a type or type component identity eight-bit word is received.

7. A teletext system according to claim 1, wherein said character generator means delivers to a matching circuit means character luminance signals, and additional logic pulses concerning the presence or the absence of basic colors R (red), V (green) or B (blue), said matching circuit means transferring the luminance signal to conventional circuits of a television receiver, said matching circuit means comprising in association with each basic color logic input a first diode having a cathode connected to an input of an analog amplifier means, switching means responsive to said keyboard means for selectively connecting an output of said basic color amplifier to a corresponding chrominance television tube input, the cathode of the first diode also being connected to cathodes of a second diode and a third diode, the first diode anode being connected from the associated color input and the output of a first voltage generator means for delivering a voltage V2, the second diode anode being connected from the output of a second voltage generator means for delivering a voltage V1, and the third diode anode being connected from the output of a third voltage generator means for delivering a voltage V3, the third voltage generator means having an output which is also connected to an output of a gate, the output of said gate not being grounded when the three color inputs simultaneously receive said logic pulses and being grounded in all other cases, with V3>V2>Vl.

8. A teletext system according to claim 1 wherein said character generator means delivers to a matching circuit means character luminance signals, and additional logic pulses concerning the presence or the absence of basic colors R (red), V (green) or B (blue), the said matching circuit means transferring the luminance signal to conventional circuits of a television receiver, said matching circuit means comprising in association with each basic color logic input a first diode having a cathode connected to an input of a basic color analog amplifier means, switching means responsive to said keyboard means for selectively connecting an output of said basic color amplifier means to the corresponding chrominance television tube input, the cathode of the first diode also being connected to the cathodes of a second diode and a third diode, the first diode anode being connected from the associated color input and the output of a first voltage generator means for delivering a voltage V2, the second diode anode being connected from the output of a second voltage generator means for delivering a voltage V1, and the third diode anode being connected from the output of a third voltage generator means for delivering a voltage V3, the third voltage generator means having an output which is also connected to the output of a gate, the output of said gate not being grounded when the three color inputs simultaneously receive said logic pulses and being grounded in all other cases, with V3>V2>Vl.