CA1044797A - Television systems - Google Patents
Television systemsInfo
- Publication number
- CA1044797A CA1044797A CA205,846A CA205846A CA1044797A CA 1044797 A CA1044797 A CA 1044797A CA 205846 A CA205846 A CA 205846A CA 1044797 A CA1044797 A CA 1044797A
- Authority
- CA
- Canada
- Prior art keywords
- characters
- received
- memory device
- digitized
- information
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N7/00—Television systems
- H04N7/08—Systems for the simultaneous or sequential transmission of more than one television signal, e.g. additional information signals, the signals occupying wholly or partially the same frequency band, e.g. by time division
- H04N7/087—Systems for the simultaneous or sequential transmission of more than one television signal, e.g. additional information signals, the signals occupying wholly or partially the same frequency band, e.g. by time division with signal insertion during the vertical blanking interval only
- H04N7/088—Systems for the simultaneous or sequential transmission of more than one television signal, e.g. additional information signals, the signals occupying wholly or partially the same frequency band, e.g. by time division with signal insertion during the vertical blanking interval only the inserted signal being digital
- H04N7/0882—Systems for the simultaneous or sequential transmission of more than one television signal, e.g. additional information signals, the signals occupying wholly or partially the same frequency band, e.g. by time division with signal insertion during the vertical blanking interval only the inserted signal being digital for the transmission of character code signals, e.g. for teletext
Landscapes
- Engineering & Computer Science (AREA)
- Multimedia (AREA)
- Signal Processing (AREA)
- Television Systems (AREA)
- Image Generation (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
The invention provides a television receiver system for collecting and storing information in the form of coded characters received separately from any wide-band picture signals. In any television system there are periods when no such picture signals are transmitted. The separately received information may be received during such periods of an actual television transmission being viewed or they may be received on a separate channel.
According to the invention, the system comprises selector equipment for selecting the information to be stored from a single information channel or a small number of information channels and routeing the selected information to a storage device, and a reading device operable, when actuated, to read the information from the storage device repeatedly and feed it, via a character generator, for display by an intensity modulated raster.
The information to be displayed may be a page selected by the viewer from a set of pages transmitted repeatedly in turn.
This selected information is held by the storing device for prolonged display.
The invention provides a television receiver system for collecting and storing information in the form of coded characters received separately from any wide-band picture signals. In any television system there are periods when no such picture signals are transmitted. The separately received information may be received during such periods of an actual television transmission being viewed or they may be received on a separate channel.
According to the invention, the system comprises selector equipment for selecting the information to be stored from a single information channel or a small number of information channels and routeing the selected information to a storage device, and a reading device operable, when actuated, to read the information from the storage device repeatedly and feed it, via a character generator, for display by an intensity modulated raster.
The information to be displayed may be a page selected by the viewer from a set of pages transmitted repeatedly in turn.
This selected information is held by the storing device for prolonged display.
Description
The present invention relates to television systems and has as an object the provision of television systems for the presentation of visual displays in a novel and convenient manner.
In any normal television system, -the transmission of the wide band video signals which are to produce the actual picture elements on the screen of the receiver, is interrupted between the scanning period for line and field synchronisation purposes. Consequently there are periods during which no video signals are being transmitted. It is now possible to use these periods for the transmission of data which is not necessarily , . .
concerned with the video transmission itself.
Basically, data representable by standard graphical symbols, such as alpha-nutneric symbols or low definition picture components can be transmitted via a restricted channel provided that the rate of transmissiorl is res-trlcted, It is now possible to use periods aqi aforesaid, especially the line times of the field blanking intervals (i.e. the times of the individual lines occurring between fields which correspond with the times occupied by video signals on active picture lines), hereinafter t'LTFB , for the transmission of pages of data. For example, using 8-bit binary digital signals of the complemented type representing alpha- `~
numeric characters at a bit rate of 2.5 M bit per second, 50 pages of data each consisting of 22 sitrips of 40 characters can be transmitted repeatedly in a total cycle time of 90 seconds using only a single line of the field blanking period per field of the 625 line system as operated in the United Kingdom. -There is accordingly a requirement for a convenient form ,!", ,.
of apparatus for use in the reception of the pages of data.
In accordance with the present invention, there is provided a television receiver system having a memory device -'`: ::.~ ..
. . ~
` _ 51342(B) form of appara-tus for use in -the reception o~ the pages of da-ta.
In accordance with -the present invention9 there is pr~vided a television receiver system having a video circuit for received video signals in the form of fields of picture signals for display by an intensity modulated raster, ~aid picture signals being separated in time by ~ield blanking intervals each of which occupies several consecutive lins pexiods, a coded-character signal memory device, selector means responsive to a chosen start code for routing to the memory device coded character signals received during the field blanking intervals and accompanied by the chosen start ~ode whilst i~noring other coded charactsr signal~ received during said intervals, a reading device operable to read the coded character signals from the memory device repeatedl~ and a character generator resporlsive to the coded chara¢ter signals read repeatedly from the memory device by the reading device to provide an output of character signals for visual display ~ -by the raster.
~or the purposes of the preserlt inventiorl, a page of a series o~`-the kirld hereinbefore described is to be -. .. . .
regarded as an information channel and the series o~ pages is ko be regarded as a series of information channels~
~he selector equipment is preferably operable to route the information to the storage device only duri~g periods of time, corresponding with the single in~ormation channel or s~all number thereof, separated by intervals which are long compared with said periods, so that the system is responsive to an information channel received 3 repeatedly at intervals. ~he said period~ may be o~ a duratio~ corresponding with several fie-ds o~ a televisio~
- 3 - ;
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signal and are distributed throu~h the LTFB periods of the signal. ~or practical purposes one or two ~B periods per field are suf~icient.
For synchronising the receiving equipment~ the portions of data may be transmitted after a run-in signal, for example of 8 identical bitso '~ypical data signals are in the form of a run-in, a start code9 address information (eOg. page nu~er, and data addres~) command bits~ spare bits and the character information. Accordingly, the selector equipment preferably incorporate~ a s-tart code comparison device and is operable to route information -to the memory device only when it is accompanied by a correct start code; the clock circuit o~ the receiver system is responsivs to the run-in and tran~itiorl~ in the data waveform and -the system incorporates address~responsive means for correctly positioning the segments~ ~he selector may have an input for a code indicative of the required channel and ~
a comparator operable to pass only si~rnals of that ~ -channel.
A sy~tem as provided by the presen-t invention may simply be provided in such a form as to provide, on a ~;
television receiver, a visual display from information transmitted during periods when no video signal is being transmitted on a television channel to which the receiver is tunsd. ~he viewer may then cause the video si~nal, the characters from -the character generator, or both~ to be displayed upon the screen of the receiver as required. It is, howeverg within the scope of the invention to arrange -Shat the memory device can be fed wi~h information transmitted during the non-video periods _ L~
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of ano-ther television channel or even -transmitted independently of any video signal over a separate data channel~ ~uch separate data channel may be a telephone ol other cable network or a radiation and receiver system.
Problems of synchronisation may be minimised by providing adequate data storage capacit~ at the reception point.
A separate data channel of low band width can be acceptable if data is transmitted for an adequate proportion of the time.
It is greatly advantageous -to employ a memory device of the continuously recirculating or other cyclically accessible type, such as a randorn access memory cyclically addressed. ~l`he stored information can then be fed to the chara¢ter ~enerator repeatedly after the memory device has beerl filled for continuous or repeated display~ even after ;' transmission of the information has ceased. ~urin~ normal operation, the memory device stores the in~`ormation from the selected channel and allows it to be displayed when- ;
.. , :
ever required and continuously for as long as required~
even though the tran~mission of th~t channel is inter-mittent (e.g. as in the case of one page selected from a set of 50).
~ or practical purposes, the character information is normally transmitted in the form of binary si~nals.
Satisfactory results under good conditions of reception such as are normally found within the main service area of a television broadcast transmitter, are obtainable by transmi-tting the signals in the simple NRZ (non return to zero) form where the zero- and one- characters are simply represented by two different signal levels, one of which is usually zero. ~or improved reception under difficult `~. ......
~v~
conditions, eOg. in fringe areas where noise is significant, the information may be transmitted in bi-phase ~orm. With this form of transmission~ each l-bit is represented by a l-level followed by a zero-level and each zero bit is represented by a zero-level follQwed by a l~level or vice versa. The rate of transmission of the information is however approximately halved compared wi-th the simple NRZ form. The band-width required with bi- ;~ ;
phase transmission is less than twice the bit-frequency. ~ ~
It is a characteristic of bi-phase si~nals that with any -series of bits (each of which involves a transi-tion between two levels, even thou~h it may be iden-tical with the preceding bit)~ the maximum interval between the transltions can never be longer than the time oocupied by one bit. Cert~in tran~mission errors are thereEore recognisable as such. ;~ -Additional advantage may be taken of the said characteristic of bi-phase signals by transmittin~ wi-th ~-every portion of data sent during a video intervalg a code in which there is at least one interval be-tween transition~
which is greater than the said maximum interval. ~'he presence of the code with the portions of data received is at least strongly indicative that the portions of data are genuine, and not, ~or example~ spurious data generated by random interference or derived accidentally ~rom some ;
other channel.
A convenient page contains 22 (horizontal) s-trips o~
40 characters. An ~FB period does not conveniently allow time ~or 40 charac-ters to be transmitted using bi-phase si~nals, though this is readily achieved usin~ simple N~Z
signals. here~ore, when bi phase signals are used each . ' "
:
, ~ . . " . .. . . . . . . .
f~
strip may be divided into segments transmitted one in each L~FB period. With four segments per strip ~transmitted in ~our successive LTFB periods), each page is constituted by 88 segmen-ts for a 22-strip page. '~he data address is in the form of a segment address, rather than a simple line address, and operates to position the segments of characters correctly on the screen.
For use with information received in the form of bi~
phase signals, the selector equipment advantageously has a pair of data registers arranged so that they are responsive to store the first and second signal levels of each digit respectively and is arranged to pass the inforr~lation to the ~emory device only if the data in one re~iste~r is the compleDIent of the other. In one preferred arr~ngement the registers of the pair are connected in parallel for -the ~ .
receipt of information and in series at other times.
Co`lveniently, the data registers are operated by a control logic circuit which arranges them for the receipt of`
informat;on only when a ætart code corresponding with a selected channel has been received.
In a presently pref`erred form o~ the system, the memory dovice is arranged to ~-tore -the inf`ormation o~ a single page selectecl from information corresponding wi-th a series o~
pages received in -turn, and -the reading device i5 operable 25 to read out the page information from the memory device -repeatedly. Compared with arrangements in which the whole of the received information in all the channels is stored, this arrangement is very economic as regards storage '' t capacity. lt does not give immediate access to a required ~0 page, but this consideration is found to be unimportant since the cycle time for as mang as 50 pages is small, even when only one L'l'~B period per field is used~
; ' ~ 7 -.... .... . i, .. .. ... .. .. .... ~, . ....... . .
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As -the character genera-tor, i-t is convenient to provide a generator of the 7 x 5 matrix type. ~his is a well know~ -type of device which need not be described in detail. It suffices to indicate that for the generation of a line of characters, -the generator must be fed with the character informa-tion seven -times in seven successive line periods~
A system as provided by the present inven-tion may be incorporated in a television receiver, the character genarator communicating with -the video circuit of the receiver. Al-ternatively, the character generator may `~
communicate with a modulator to provide a carrier modula-ted by video si~nals representing the information. '~he latter arran~ement may be used in an adaptor unit ~or connection in the aerial cable o~ an existing receiver so that the receiver may be employed for the present purpose without in-ternal modification.
~he following description in which reference is made to the accompanying drawings is given in order -to illustra-te the invention. In the drawings: -is a block diagram showing a normal television receiver modi~ied b~ the additlon of a sys-tem as provlded by the invention, and Figures 2 and ~ are block diagrams showing parts of the system shown in ~-igure l in ~urther ~ -detail, and ~ -_i~ure 4 is a dlagram illustra-ting the form o~ the da-ta handled~ and Fi~res 5A, 5B,_5C and 5D relate to a character rounding system which may advantageously be employedO
~ 8 -$7' Figs. ~, 3 and 4 are concerned with signals of the bi-phase type and a system for the reception thereof.
~p~ropriately modified apparatus may be provided for use with signals of the simple NRZ type.
Referring to ~ig. 1, the demodulated television signal to which the television receiver is tuned is taken from the receiver 11 at an emitter follo~Jer point. The signal contain3 6 MHz F/M sound which is ~iltered by ~ilter 120 The signal is then a~plified to provide several feeds of 75 ohm video.
The sync separator derives 7 ~rom the incoming demodulated signal, line and field rate timing pulses which are u3ed in various parts of the system.
One video ~eed ~oes direct to part 3 which for simplicity ma~ be regarded as a video switch.
A second video ~eed to the video switch goes via a text adder. The tex-t adder adds a controlled ~mount of current to this video signal so -that captions are effectively superimposed on the picture corresponding to this video patha A third video feed passes to -the data receiver. The data receiver is exposed to the whole video si~nal~ and C~l pick out tho data si~nal~ discriminatin~ agalns-t normal picture signals. Alternati~ely, the data receiver might be enabled only during the appropriate time5 when the data lines occur in the si~nal.
The data receiver presents the data -to the stores of the Text Signal Generator. rrhis generates the appropriate text signal a-t logical (Transistor-Transistor Logic) voltage levels.
rrhe text signal is used to control the text adder and is also pas~ed via a filter and a converter which chan~es the signal to 75 Ohm video level. r~his video text signal then passes to another input of the video switch.
The output of the video switch is either input 1, 2 or 3 in the diagram. r~his passes through an amplifier and returns the signal -to the luminance channel of the se-t (at approximately 5 volts peak to peak in this case).
Control of the display i5 effected by pre~sing the ;~
appropriate button on the display selec-tor. Possibilities are as follows:-Bu-t-ton Video Switch Out~ut Picture only Input 1 Picture f text (added) Inpu-t 2 ~ic-ture ~ -te~t (non Input 1 and 2 ~whichever addi-tive) is instantaneously greater) simultaneously r~ext only (black or white Input 3.
text) r~he display control ensures tha-t correc-t timing is maintained as follows.
r~ext is only produced during active line -time (no-t during line sync pulses) r~ext is not produced ~uring Pield blankin~. -r~he video switch always passes -the input 1 to the ou-tput durin~ line and field sync times~
This ensures that the output always contains -the correct television synchronisin~ puDses~ `
Black text or white text is effected by either using normal or inverted polarity text signal under control from the display selector and display control.
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The display selector also contains a connection -to the set which enables the sound ou-tput o~ the set to be mutedO
In an alternative arrangement, instead of taking a de-modulated signal from the television receiver, an adapter is connected in the aerial lead~ In this case the input -to the system is at R~Fo '~his is demodulated -to video and a similar process performed on the video signal as just describedO The resultant video is then re-modulated and ~assed to the aerial input of the television receiver on an appropriate channel.
If data from one television channel is to be dis-played over another television channel, then a second R.F.
dernodulator is required, one to provide the data~ the other for the normal television prograln~e.
'I`he sy~tem o~ Eli~ure 1 may be rnodified to include coloured captions. In thi~ case direct access to -the Red, ''' Green, Blue guns of the television receiver is the simplest solution. An Ro~ aerial lead adaptor would also be possible.
'The psrt marked "Data Receiver" in Figure 1 i5 shown in detail in Fi~ure 2. As shown in L'~ ure 4, the data format consists of 16 parts of varying len~th excludin~
the run in. After the start code t'he si~nal is in the form of bi-phase bits and the character signals are in a standard AS~II code~ -Referring now to Fi~. 2, the DATA PICK 0F~ and CLOCK
~GENERATOR presents the DA'~A ROUTING CI~CUI~ with -the da~a and re~enerated clock at standard TTL lo~ic levels~ ' Until a start code has been received the DA'lA
REGI~ ~ ~ and B are connected in series via the DA'~A
ROUTING CIRCUIT and data is continuously shifted througrh ~r . .
,.
r;~ 9 `.j.
the D~'~A REGI~ER~o 'l'he receiver recognises a star-t code by con-tinuously comparing -the contents of DA'I'A REGIS'~ER B
wi-th the start code applied to -the DATA CO~ARA'~OR via the COMPARE DA'~A MUL'~IPLEXER. r~he contents of DA'~A REGIS'~RS ~ -~ and B are also compared in the COMPLEMEN'~ CHECK CIRCUI' to see if the halves o~ the start code complement each .~ :.
other. When a correct start code has been received the ::
~ON'~XOL LOGIG. will store this and increment the DECODE
COUNTER by 1 which now points to the part of the data ;.
containin~ the line number.
'rhe CON'rROL LOGIG ins-tructs the COMPA~.DA'~A ..
MUL'rIP~EXER.to apply the selected line number to the ~oM~ARA~r~olt and connects the ~A'~A REGIS'rERS A and B in parallel via the DA'l'~ ROU'~ING CIRCUI'~. A '~WO PHASE CLOCK
15 is applied to the ~A'rA XEGIS'~æRS clocking REGIS'~ER A ~irst ...
and then Bo As a BI-P~IAS~.transmission ~ode is used, the .. - .
~irst element of each bit is shifted into ~A~A REGISTER A
and the ~econd element into B~ '~herefoxe DA~A REGIS'~ER B .
will contain the inverse da-ta of DAr~A REGIS~ER A. ~ .
After the correct start code has been received and the next 5 bits have been demultiplexed by the two phase clock action and shi~ted in-to DAr~A REGISr~E~S A and B a strobe pulse is genera-ted by the BI~ COUNr~ER -to compare the received data with the selected data label and to check if the contents of DA~A REGIS~ERS A and B co~lement each o-ther. If so5 this again is stored in the CON~ROL ~OGIC ~ .
which in turn will increment the DECODE COUN~ER by 1 9 pointing now to the part of the data con-taining the page .: . .
number, ....
A further 6 bits are demultiplexed and shifted into the DA~A REGIS~ERS A and B. A strobe pulse is again - 12 ~
'''' '~ '' ' ' .
'.', " ' ~
~L O ~ r~
~enerated by the BIT COUN~ER to compare the received data . : :
wi-th the selected page number and to check if the contents of the -two REGISr~ERS A and B complement each otherO r~his again is stored in the CON'~ROL ~OGIC which increments the D~CO~E COUNr~ER by 1, pointing now to the part of the data containing the strip and segment numbers.
If the correct start code and sel.ected-line and page number have been received the control logi.c will pass the next 13 par-ts of the data (96 bits in 12 8-bit groups) on to the DISPLAY via the OU'~PU'~ DA~A SELEC~'OR and ~AI'A !''~
BUF~EX Sr~ORE. If at any time a complementatio~ error is found within an 8-bit group, a blank is passed on to the i~
DISP~AY instead o~ the received data within that group.
A~ter the 13 -~art~ have been passed on to the DISP~Y the control unit will reset, ready to receive another start code and new d~ta and the cycle is repeated~
Fig. 3 shows further details of the part marked "~ex-t Signal Generator" in Figure 1. Data is received in the ~orm o~ eight-bit parallel words on an eight wire input from the data received from the apparatus of ~'igure 20 rl'hese words are presented to the input o~ a segment store 16, con~i~ting o~ eight 16-bit serial-in parallel-out :
shift registers. When each word is presented to the input o~ the store 16, a strobe pulse is app~iod thus entering ~.
the data. r~welve words are clocked into the store~ the ~ -first o~ which denotes the row and segment addressO I~
transmission is on two lines per field, two similar segment stores are required, one for each data line :
re¢eived in the ~ield blanking time.
~'he page store 17 into which -the incoming data is clocked at the appropriate time consists o~ six 1024-bit : '' - 13 - :
':' shif-t registers. ~his page store then feeds into a strip ~
s-tore which consists of six 40-bit shift registers. ~he ; -output of -the strip store addresses a character genera-tor via a blanking generator.
I~ order -to print a chara~,ter on -the television screen the ~II code for that character must be presented to the display generator at the appropriate times on the appropriate lines of the field scan. Since a charac-~r generator of th~ 7 ~ 5 matrix type is used, this ASCII
character code must be presented to the display generator seven -times whilst the row number is stepped ~rom 1 through 7. In order to display a strip of ~0 characters on the screen -the strip store mu,st be rotated 7 time~
(once per ~can line) whil~t th0 row number is s~eppod from 1 through 7.
For the display of a full page of in~ormation the page store must be rotated ~ully once per picture field, but only in steps of 40 characters corresponding -to the last rotation of the strip store.
In fact the strip store is only actually ro-tated 6 timas and on the seventh row the output of the s-trip ~tore is entered into the fron-t of the page store~
~wenty two strips of characters are generated on the screen and each of these consis-ts of four segmen-ts.
As the strip store is rotated the seventh time, segment addresses O through ~ are generated internally a~d are compared wi-th the inpu-t segment number which appears a-t the twelfth posi-tion in the line store. ~;
Immediately after each seventh rotation of -the strip s-tore, a strip number counter is incremented by one step through tha range 1 to 22 and this is compared '. :' " :
~,,.
': ; ': ' with the input s-trip address. ~hen strip and segment address of input data and currently displayed data are the same, the page store is switched to accept data from the segment store 16. As soon as the local segment address is incremented the page store switches ba,ck to accepting data ~rom -the strip store.
When a page of data is initially selecte~ one ~full rotation of the page store is completed with the blanking generator switched on, thus emptying the store of the previous informationO ~he receiver will display a blank screen until such a time that it receives appropriate new data from the -text signal generator. ;
r~he extr~me left- and right-hand se~ments of strip 1 of all pages may possess a transparent pa~e number of ~u¢h oharacter that they are displayed whiohever pa~e is selected. ~he left-hand segment may contain the page number actually being transmitted at the particular time, and the right-hand segment may contain the time of day accurate to one second.
A character rounding s~stem may be provided for improved results. In a preferred syste~, the main characters are generated in a 7 x 5 matrix arrangement and roun~ing bits of the characters are generated in a 6 x 4 matrix arrangement and superposed in a staggered arrangement - see ~i~ures 5A and 5C. This system is very i~ ;
¢onvenient with interlaced scanni~g. -~he results are preferable to those shown in ~igure 5B
obtained with a syst~m which relies upon generating round- ;;
ing bits when diagonals are detected - compare~igures 5 and 5C.
The 7 x 5 and 6 x 4 read only memories (ROn's) . . .
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.. .. . - ... , .. :. , ., . ", .. , , . .. , . . " , . .....
d~7 : ~ ~
required can be produced by s-tandard integrated circuit - :
manufacturing techniques, ~he two ROM's must be addressed : :; :
. .; . . ..
in an out of step fashion, requiring the iden-ti~ication of the two fields involved. ~igure 5D shows an example o~ a circuit for combining the output of the ROM's. .`
Reference has been made herein to symbols in the form of low definition picture components as an example of . -graphical symbols which can be transmittedO O~ especial - . :
interest are symbols derived by filling the positions of a matrix in the various possible combinations. ~ 3 x 2 matrix~ i.e. a matrix having three horizontal rows with .
two positions in each gives 62 possible graphical symbols derived by inserting from 1 to 5 dots in various distribution~ in addition to tht possibilities of a `;
completely full and a comp:letely empty matrix wh.ich a:re to be regartled as two further grclphical symbols. Using symbols of this type arranged, like alpha-numeric symbols .
on a series of lines, still pictorial matter can be formed.
. .
'~he character generator of the present equipmen-t is there- ..
fore usefully arranged -to generate such graphical symbols, instead.of alpha-numeric symbols, ln response to . ~ :
~'~propriate commands received with the transmission. .-: ' ~ :: . , ' . ' :' ' , . ~ .
' ' .,:
,':~', ~ ' ' .;: ' .:: .
, -. ' '
In any normal television system, -the transmission of the wide band video signals which are to produce the actual picture elements on the screen of the receiver, is interrupted between the scanning period for line and field synchronisation purposes. Consequently there are periods during which no video signals are being transmitted. It is now possible to use these periods for the transmission of data which is not necessarily , . .
concerned with the video transmission itself.
Basically, data representable by standard graphical symbols, such as alpha-nutneric symbols or low definition picture components can be transmitted via a restricted channel provided that the rate of transmissiorl is res-trlcted, It is now possible to use periods aqi aforesaid, especially the line times of the field blanking intervals (i.e. the times of the individual lines occurring between fields which correspond with the times occupied by video signals on active picture lines), hereinafter t'LTFB , for the transmission of pages of data. For example, using 8-bit binary digital signals of the complemented type representing alpha- `~
numeric characters at a bit rate of 2.5 M bit per second, 50 pages of data each consisting of 22 sitrips of 40 characters can be transmitted repeatedly in a total cycle time of 90 seconds using only a single line of the field blanking period per field of the 625 line system as operated in the United Kingdom. -There is accordingly a requirement for a convenient form ,!", ,.
of apparatus for use in the reception of the pages of data.
In accordance with the present invention, there is provided a television receiver system having a memory device -'`: ::.~ ..
. . ~
` _ 51342(B) form of appara-tus for use in -the reception o~ the pages of da-ta.
In accordance with -the present invention9 there is pr~vided a television receiver system having a video circuit for received video signals in the form of fields of picture signals for display by an intensity modulated raster, ~aid picture signals being separated in time by ~ield blanking intervals each of which occupies several consecutive lins pexiods, a coded-character signal memory device, selector means responsive to a chosen start code for routing to the memory device coded character signals received during the field blanking intervals and accompanied by the chosen start ~ode whilst i~noring other coded charactsr signal~ received during said intervals, a reading device operable to read the coded character signals from the memory device repeatedl~ and a character generator resporlsive to the coded chara¢ter signals read repeatedly from the memory device by the reading device to provide an output of character signals for visual display ~ -by the raster.
~or the purposes of the preserlt inventiorl, a page of a series o~`-the kirld hereinbefore described is to be -. .. . .
regarded as an information channel and the series o~ pages is ko be regarded as a series of information channels~
~he selector equipment is preferably operable to route the information to the storage device only duri~g periods of time, corresponding with the single in~ormation channel or s~all number thereof, separated by intervals which are long compared with said periods, so that the system is responsive to an information channel received 3 repeatedly at intervals. ~he said period~ may be o~ a duratio~ corresponding with several fie-ds o~ a televisio~
- 3 - ;
~, J~ 'd ;~
signal and are distributed throu~h the LTFB periods of the signal. ~or practical purposes one or two ~B periods per field are suf~icient.
For synchronising the receiving equipment~ the portions of data may be transmitted after a run-in signal, for example of 8 identical bitso '~ypical data signals are in the form of a run-in, a start code9 address information (eOg. page nu~er, and data addres~) command bits~ spare bits and the character information. Accordingly, the selector equipment preferably incorporate~ a s-tart code comparison device and is operable to route information -to the memory device only when it is accompanied by a correct start code; the clock circuit o~ the receiver system is responsivs to the run-in and tran~itiorl~ in the data waveform and -the system incorporates address~responsive means for correctly positioning the segments~ ~he selector may have an input for a code indicative of the required channel and ~
a comparator operable to pass only si~rnals of that ~ -channel.
A sy~tem as provided by the presen-t invention may simply be provided in such a form as to provide, on a ~;
television receiver, a visual display from information transmitted during periods when no video signal is being transmitted on a television channel to which the receiver is tunsd. ~he viewer may then cause the video si~nal, the characters from -the character generator, or both~ to be displayed upon the screen of the receiver as required. It is, howeverg within the scope of the invention to arrange -Shat the memory device can be fed wi~h information transmitted during the non-video periods _ L~
''.,' :' '1~ . '. ':
.. ~. . ...
:
~q3 f~ r~
of ano-ther television channel or even -transmitted independently of any video signal over a separate data channel~ ~uch separate data channel may be a telephone ol other cable network or a radiation and receiver system.
Problems of synchronisation may be minimised by providing adequate data storage capacit~ at the reception point.
A separate data channel of low band width can be acceptable if data is transmitted for an adequate proportion of the time.
It is greatly advantageous -to employ a memory device of the continuously recirculating or other cyclically accessible type, such as a randorn access memory cyclically addressed. ~l`he stored information can then be fed to the chara¢ter ~enerator repeatedly after the memory device has beerl filled for continuous or repeated display~ even after ;' transmission of the information has ceased. ~urin~ normal operation, the memory device stores the in~`ormation from the selected channel and allows it to be displayed when- ;
.. , :
ever required and continuously for as long as required~
even though the tran~mission of th~t channel is inter-mittent (e.g. as in the case of one page selected from a set of 50).
~ or practical purposes, the character information is normally transmitted in the form of binary si~nals.
Satisfactory results under good conditions of reception such as are normally found within the main service area of a television broadcast transmitter, are obtainable by transmi-tting the signals in the simple NRZ (non return to zero) form where the zero- and one- characters are simply represented by two different signal levels, one of which is usually zero. ~or improved reception under difficult `~. ......
~v~
conditions, eOg. in fringe areas where noise is significant, the information may be transmitted in bi-phase ~orm. With this form of transmission~ each l-bit is represented by a l-level followed by a zero-level and each zero bit is represented by a zero-level follQwed by a l~level or vice versa. The rate of transmission of the information is however approximately halved compared wi-th the simple NRZ form. The band-width required with bi- ;~ ;
phase transmission is less than twice the bit-frequency. ~ ~
It is a characteristic of bi-phase si~nals that with any -series of bits (each of which involves a transi-tion between two levels, even thou~h it may be iden-tical with the preceding bit)~ the maximum interval between the transltions can never be longer than the time oocupied by one bit. Cert~in tran~mission errors are thereEore recognisable as such. ;~ -Additional advantage may be taken of the said characteristic of bi-phase signals by transmittin~ wi-th ~-every portion of data sent during a video intervalg a code in which there is at least one interval be-tween transition~
which is greater than the said maximum interval. ~'he presence of the code with the portions of data received is at least strongly indicative that the portions of data are genuine, and not, ~or example~ spurious data generated by random interference or derived accidentally ~rom some ;
other channel.
A convenient page contains 22 (horizontal) s-trips o~
40 characters. An ~FB period does not conveniently allow time ~or 40 charac-ters to be transmitted using bi-phase si~nals, though this is readily achieved usin~ simple N~Z
signals. here~ore, when bi phase signals are used each . ' "
:
, ~ . . " . .. . . . . . . .
f~
strip may be divided into segments transmitted one in each L~FB period. With four segments per strip ~transmitted in ~our successive LTFB periods), each page is constituted by 88 segmen-ts for a 22-strip page. '~he data address is in the form of a segment address, rather than a simple line address, and operates to position the segments of characters correctly on the screen.
For use with information received in the form of bi~
phase signals, the selector equipment advantageously has a pair of data registers arranged so that they are responsive to store the first and second signal levels of each digit respectively and is arranged to pass the inforr~lation to the ~emory device only if the data in one re~iste~r is the compleDIent of the other. In one preferred arr~ngement the registers of the pair are connected in parallel for -the ~ .
receipt of information and in series at other times.
Co`lveniently, the data registers are operated by a control logic circuit which arranges them for the receipt of`
informat;on only when a ætart code corresponding with a selected channel has been received.
In a presently pref`erred form o~ the system, the memory dovice is arranged to ~-tore -the inf`ormation o~ a single page selectecl from information corresponding wi-th a series o~
pages received in -turn, and -the reading device i5 operable 25 to read out the page information from the memory device -repeatedly. Compared with arrangements in which the whole of the received information in all the channels is stored, this arrangement is very economic as regards storage '' t capacity. lt does not give immediate access to a required ~0 page, but this consideration is found to be unimportant since the cycle time for as mang as 50 pages is small, even when only one L'l'~B period per field is used~
; ' ~ 7 -.... .... . i, .. .. ... .. .. .... ~, . ....... . .
7~ ~
As -the character genera-tor, i-t is convenient to provide a generator of the 7 x 5 matrix type. ~his is a well know~ -type of device which need not be described in detail. It suffices to indicate that for the generation of a line of characters, -the generator must be fed with the character informa-tion seven -times in seven successive line periods~
A system as provided by the present inven-tion may be incorporated in a television receiver, the character genarator communicating with -the video circuit of the receiver. Al-ternatively, the character generator may `~
communicate with a modulator to provide a carrier modula-ted by video si~nals representing the information. '~he latter arran~ement may be used in an adaptor unit ~or connection in the aerial cable o~ an existing receiver so that the receiver may be employed for the present purpose without in-ternal modification.
~he following description in which reference is made to the accompanying drawings is given in order -to illustra-te the invention. In the drawings: -is a block diagram showing a normal television receiver modi~ied b~ the additlon of a sys-tem as provlded by the invention, and Figures 2 and ~ are block diagrams showing parts of the system shown in ~-igure l in ~urther ~ -detail, and ~ -_i~ure 4 is a dlagram illustra-ting the form o~ the da-ta handled~ and Fi~res 5A, 5B,_5C and 5D relate to a character rounding system which may advantageously be employedO
~ 8 -$7' Figs. ~, 3 and 4 are concerned with signals of the bi-phase type and a system for the reception thereof.
~p~ropriately modified apparatus may be provided for use with signals of the simple NRZ type.
Referring to ~ig. 1, the demodulated television signal to which the television receiver is tuned is taken from the receiver 11 at an emitter follo~Jer point. The signal contain3 6 MHz F/M sound which is ~iltered by ~ilter 120 The signal is then a~plified to provide several feeds of 75 ohm video.
The sync separator derives 7 ~rom the incoming demodulated signal, line and field rate timing pulses which are u3ed in various parts of the system.
One video ~eed ~oes direct to part 3 which for simplicity ma~ be regarded as a video switch.
A second video ~eed to the video switch goes via a text adder. The tex-t adder adds a controlled ~mount of current to this video signal so -that captions are effectively superimposed on the picture corresponding to this video patha A third video feed passes to -the data receiver. The data receiver is exposed to the whole video si~nal~ and C~l pick out tho data si~nal~ discriminatin~ agalns-t normal picture signals. Alternati~ely, the data receiver might be enabled only during the appropriate time5 when the data lines occur in the si~nal.
The data receiver presents the data -to the stores of the Text Signal Generator. rrhis generates the appropriate text signal a-t logical (Transistor-Transistor Logic) voltage levels.
rrhe text signal is used to control the text adder and is also pas~ed via a filter and a converter which chan~es the signal to 75 Ohm video level. r~his video text signal then passes to another input of the video switch.
The output of the video switch is either input 1, 2 or 3 in the diagram. r~his passes through an amplifier and returns the signal -to the luminance channel of the se-t (at approximately 5 volts peak to peak in this case).
Control of the display i5 effected by pre~sing the ;~
appropriate button on the display selec-tor. Possibilities are as follows:-Bu-t-ton Video Switch Out~ut Picture only Input 1 Picture f text (added) Inpu-t 2 ~ic-ture ~ -te~t (non Input 1 and 2 ~whichever addi-tive) is instantaneously greater) simultaneously r~ext only (black or white Input 3.
text) r~he display control ensures tha-t correc-t timing is maintained as follows.
r~ext is only produced during active line -time (no-t during line sync pulses) r~ext is not produced ~uring Pield blankin~. -r~he video switch always passes -the input 1 to the ou-tput durin~ line and field sync times~
This ensures that the output always contains -the correct television synchronisin~ puDses~ `
Black text or white text is effected by either using normal or inverted polarity text signal under control from the display selector and display control.
- 10 ~
'" '.'. `. ,.
:' . '; .
The display selector also contains a connection -to the set which enables the sound ou-tput o~ the set to be mutedO
In an alternative arrangement, instead of taking a de-modulated signal from the television receiver, an adapter is connected in the aerial lead~ In this case the input -to the system is at R~Fo '~his is demodulated -to video and a similar process performed on the video signal as just describedO The resultant video is then re-modulated and ~assed to the aerial input of the television receiver on an appropriate channel.
If data from one television channel is to be dis-played over another television channel, then a second R.F.
dernodulator is required, one to provide the data~ the other for the normal television prograln~e.
'I`he sy~tem o~ Eli~ure 1 may be rnodified to include coloured captions. In thi~ case direct access to -the Red, ''' Green, Blue guns of the television receiver is the simplest solution. An Ro~ aerial lead adaptor would also be possible.
'The psrt marked "Data Receiver" in Figure 1 i5 shown in detail in Fi~ure 2. As shown in L'~ ure 4, the data format consists of 16 parts of varying len~th excludin~
the run in. After the start code t'he si~nal is in the form of bi-phase bits and the character signals are in a standard AS~II code~ -Referring now to Fi~. 2, the DATA PICK 0F~ and CLOCK
~GENERATOR presents the DA'~A ROUTING CI~CUI~ with -the da~a and re~enerated clock at standard TTL lo~ic levels~ ' Until a start code has been received the DA'lA
REGI~ ~ ~ and B are connected in series via the DA'~A
ROUTING CIRCUIT and data is continuously shifted througrh ~r . .
,.
r;~ 9 `.j.
the D~'~A REGI~ER~o 'l'he receiver recognises a star-t code by con-tinuously comparing -the contents of DA'I'A REGIS'~ER B
wi-th the start code applied to -the DATA CO~ARA'~OR via the COMPARE DA'~A MUL'~IPLEXER. r~he contents of DA'~A REGIS'~RS ~ -~ and B are also compared in the COMPLEMEN'~ CHECK CIRCUI' to see if the halves o~ the start code complement each .~ :.
other. When a correct start code has been received the ::
~ON'~XOL LOGIG. will store this and increment the DECODE
COUNTER by 1 which now points to the part of the data ;.
containin~ the line number.
'rhe CON'rROL LOGIG ins-tructs the COMPA~.DA'~A ..
MUL'rIP~EXER.to apply the selected line number to the ~oM~ARA~r~olt and connects the ~A'~A REGIS'rERS A and B in parallel via the DA'l'~ ROU'~ING CIRCUI'~. A '~WO PHASE CLOCK
15 is applied to the ~A'rA XEGIS'~æRS clocking REGIS'~ER A ~irst ...
and then Bo As a BI-P~IAS~.transmission ~ode is used, the .. - .
~irst element of each bit is shifted into ~A~A REGISTER A
and the ~econd element into B~ '~herefoxe DA~A REGIS'~ER B .
will contain the inverse da-ta of DAr~A REGIS~ER A. ~ .
After the correct start code has been received and the next 5 bits have been demultiplexed by the two phase clock action and shi~ted in-to DAr~A REGISr~E~S A and B a strobe pulse is genera-ted by the BI~ COUNr~ER -to compare the received data with the selected data label and to check if the contents of DA~A REGIS~ERS A and B co~lement each o-ther. If so5 this again is stored in the CON~ROL ~OGIC ~ .
which in turn will increment the DECODE COUN~ER by 1 9 pointing now to the part of the data con-taining the page .: . .
number, ....
A further 6 bits are demultiplexed and shifted into the DA~A REGIS~ERS A and B. A strobe pulse is again - 12 ~
'''' '~ '' ' ' .
'.', " ' ~
~L O ~ r~
~enerated by the BIT COUN~ER to compare the received data . : :
wi-th the selected page number and to check if the contents of the -two REGISr~ERS A and B complement each otherO r~his again is stored in the CON'~ROL ~OGIC which increments the D~CO~E COUNr~ER by 1, pointing now to the part of the data containing the strip and segment numbers.
If the correct start code and sel.ected-line and page number have been received the control logi.c will pass the next 13 par-ts of the data (96 bits in 12 8-bit groups) on to the DISPLAY via the OU'~PU'~ DA~A SELEC~'OR and ~AI'A !''~
BUF~EX Sr~ORE. If at any time a complementatio~ error is found within an 8-bit group, a blank is passed on to the i~
DISP~AY instead o~ the received data within that group.
A~ter the 13 -~art~ have been passed on to the DISP~Y the control unit will reset, ready to receive another start code and new d~ta and the cycle is repeated~
Fig. 3 shows further details of the part marked "~ex-t Signal Generator" in Figure 1. Data is received in the ~orm o~ eight-bit parallel words on an eight wire input from the data received from the apparatus of ~'igure 20 rl'hese words are presented to the input o~ a segment store 16, con~i~ting o~ eight 16-bit serial-in parallel-out :
shift registers. When each word is presented to the input o~ the store 16, a strobe pulse is app~iod thus entering ~.
the data. r~welve words are clocked into the store~ the ~ -first o~ which denotes the row and segment addressO I~
transmission is on two lines per field, two similar segment stores are required, one for each data line :
re¢eived in the ~ield blanking time.
~'he page store 17 into which -the incoming data is clocked at the appropriate time consists o~ six 1024-bit : '' - 13 - :
':' shif-t registers. ~his page store then feeds into a strip ~
s-tore which consists of six 40-bit shift registers. ~he ; -output of -the strip store addresses a character genera-tor via a blanking generator.
I~ order -to print a chara~,ter on -the television screen the ~II code for that character must be presented to the display generator at the appropriate times on the appropriate lines of the field scan. Since a charac-~r generator of th~ 7 ~ 5 matrix type is used, this ASCII
character code must be presented to the display generator seven -times whilst the row number is stepped ~rom 1 through 7. In order to display a strip of ~0 characters on the screen -the strip store mu,st be rotated 7 time~
(once per ~can line) whil~t th0 row number is s~eppod from 1 through 7.
For the display of a full page of in~ormation the page store must be rotated ~ully once per picture field, but only in steps of 40 characters corresponding -to the last rotation of the strip store.
In fact the strip store is only actually ro-tated 6 timas and on the seventh row the output of the s-trip ~tore is entered into the fron-t of the page store~
~wenty two strips of characters are generated on the screen and each of these consis-ts of four segmen-ts.
As the strip store is rotated the seventh time, segment addresses O through ~ are generated internally a~d are compared wi-th the inpu-t segment number which appears a-t the twelfth posi-tion in the line store. ~;
Immediately after each seventh rotation of -the strip s-tore, a strip number counter is incremented by one step through tha range 1 to 22 and this is compared '. :' " :
~,,.
': ; ': ' with the input s-trip address. ~hen strip and segment address of input data and currently displayed data are the same, the page store is switched to accept data from the segment store 16. As soon as the local segment address is incremented the page store switches ba,ck to accepting data ~rom -the strip store.
When a page of data is initially selecte~ one ~full rotation of the page store is completed with the blanking generator switched on, thus emptying the store of the previous informationO ~he receiver will display a blank screen until such a time that it receives appropriate new data from the -text signal generator. ;
r~he extr~me left- and right-hand se~ments of strip 1 of all pages may possess a transparent pa~e number of ~u¢h oharacter that they are displayed whiohever pa~e is selected. ~he left-hand segment may contain the page number actually being transmitted at the particular time, and the right-hand segment may contain the time of day accurate to one second.
A character rounding s~stem may be provided for improved results. In a preferred syste~, the main characters are generated in a 7 x 5 matrix arrangement and roun~ing bits of the characters are generated in a 6 x 4 matrix arrangement and superposed in a staggered arrangement - see ~i~ures 5A and 5C. This system is very i~ ;
¢onvenient with interlaced scanni~g. -~he results are preferable to those shown in ~igure 5B
obtained with a syst~m which relies upon generating round- ;;
ing bits when diagonals are detected - compare~igures 5 and 5C.
The 7 x 5 and 6 x 4 read only memories (ROn's) . . .
. -: : ''.. ".
.. .. . - ... , .. :. , ., . ", .. , , . .. , . . " , . .....
d~7 : ~ ~
required can be produced by s-tandard integrated circuit - :
manufacturing techniques, ~he two ROM's must be addressed : :; :
. .; . . ..
in an out of step fashion, requiring the iden-ti~ication of the two fields involved. ~igure 5D shows an example o~ a circuit for combining the output of the ROM's. .`
Reference has been made herein to symbols in the form of low definition picture components as an example of . -graphical symbols which can be transmittedO O~ especial - . :
interest are symbols derived by filling the positions of a matrix in the various possible combinations. ~ 3 x 2 matrix~ i.e. a matrix having three horizontal rows with .
two positions in each gives 62 possible graphical symbols derived by inserting from 1 to 5 dots in various distribution~ in addition to tht possibilities of a `;
completely full and a comp:letely empty matrix wh.ich a:re to be regartled as two further grclphical symbols. Using symbols of this type arranged, like alpha-numeric symbols .
on a series of lines, still pictorial matter can be formed.
. .
'~he character generator of the present equipmen-t is there- ..
fore usefully arranged -to generate such graphical symbols, instead.of alpha-numeric symbols, ln response to . ~ :
~'~propriate commands received with the transmission. .-: ' ~ :: . , ' . ' :' ' , . ~ .
' ' .,:
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, -. ' '
Claims (21)
1. A television receiver system having a video circuit for received video signals in the form of fields of picture signals for display by an intensity modulated raster, said picture signals being separated in time by field blanking intervals each of which occupies several consecutive line periods, a coded-character signal memory device, selector means responsive to a chosen start code for routing to the memory device coded character signals received during the field blanking intervals and accompanied by the chosen start code whilst ignoring other coded character signals received during said intervals, a reading device operable to read the coded character signals from the memory device repeatedly and a character generator responsive to the coded character signals read repeatedly from the memory device by the reading device to provide an output of character signals for visual display by the raster.
2. A television receiver system having a memory device, a clocking device for actuating the memory device, an input for a set of pages of information received at said input in the form of digitized characters in a repeated cycle the form of which is such that the digitized characters for the set of pages are received in groups of the characters, and the whole of the information for the set of pages is received during each occurrence of the cycle, each group as received being preceded by a clock run-in signal, to which the clocking device is responsive for synchronization, followed by a known start code correct receipt of which indicates integrity of reception and also followed by a page address code, variable selector means for selecting a page from the set of pages and routing a group of digitized characters to the memory device when the preceding start code is received correctly and the preceding page address code corresponds with the selected page while disregarding digitized groups of characters preceded by a page address code other than that selected, a reading device operable to read the digitized characters repeatedly from the memory device, and a character generator responsive to the digitized characters read by the reading device to provide output signals for visual display by an intensity modulated raster of the television reception type.
3. A system according to Claim 2 for use with information received in the form of binary numbers representing the characters, with each digit represented by one signal level followed by another signal level, in which the selector equipment has a pair of data registers arranged so that they are responsive to store the first and second signal levels of each digit respectively and is arranged to pass the information to the memory device only if the data in one register is the complement of the other.
4. A system according to Claim 3 in which the data registers of the pair are connected in parallel for the receipt of information and in series at other times.
5. A system according to Claim 3 in which the data registers are operated by a control logic circuit which arranges them for the receipt of information only when a start code corresponding with a selected channel has been received.
6. A system according to Claim 2 in which the selector has an input for a code indicative of the required channel and a comparator operable to pass only signals of that channel.
7. A system according to Claim 2 in which the memory device is arranged to store the information of a single page selected from information corresponding with a series of pages received in turn, and the reading device is operable to read out the page information from the memory device repeatedly.
8. A television receiver incorporating a system according to Claim 2, the character generator communicating with the video circuit of the receiver.
9. A system according to Claim 2 in which the character generator communicates with a modulator to provide a carrier modulated by video signals representing the information.
10. A system according to Claim 2 in which the memory device is of the continuously re-circulating type.
11. A system according to Claim 2 in which the memory device is of the cyclically addressed type.
12. A system according to Claim 2 having a demodulator for television signals, said demodulator being connected with said input.
13. A system according to Claim 2 having a second character generator responsive to the digitized characters, said character generator being operable to provide character rounding bits for superposition on the visual display.
14. A television receiver system having a memory device, a clocking device for actuating the memory device, an input for a set of pages of information received at said input in the form of digitized characters in a repeated cycle the form of which is such that the digitized characters for the set of pages are received in groups of the characters, and the whole of the information for the set of pages is received during each occurrence of the cycle, each group as received being preceded by a clock run-in signal, to which the clocking device is responsive for synchronization, followed by a known start code correct receipt of which indicates integrity of reception and also followed by a page address code, variable selector means for selecting a page from the set of pages and routing a group of digitized characters to the memory device when the preceding start code is received correctly and the preceding page address code corresponds with the selected page while disregarding digitized groups of characters preceded by an incorrectly received start code and groups of characters preceded by a page address code other than that selected, a reading device operable to read the digitized characters repeatedly from the memory device, a character generator responsive to the digitized characters read by the reading device to provide output signals for visual display by an intensity modulated raster, a modulator connected with an output for the output signals and operable to provide a television carrier modulated by the output signals and a television receiver responsive to said modulated carrier for providing said display, said carrier having a frequency to which the receiver is tunable.
15. A system according to claim 14 in which the television receiver has a television antenna input and said antenna input is connected with said modulator.
16. A television receiver system having a television receiver with an RF input, a demodulator, a video circuit fed by the demodulator and a visual display for displaying picture signals as an intensity-modulated raster, a memory device, a clocking device for actuating the memory device, an output from the video circuit for data received at said RF input and demodulated by the demodulator, said data representing a set of pages of information in the form of digitized characters in a repeated cycle the form of which is such that the digitized characters for the set of pages are received repeatedly in groups of the characters and the whole of the information for the set of pages is received during each occurrence of the cycle, each group as received being preceded by a clock run-in signal, to which the clocking device is responsive fox synchronization, followed by a known start code correct receipt of which indicates integrity of reception and also followed by a page address code, variable selector means for selecting a page from the set of pages and routing a group of digitized characters to the memory device when the preceding start code is received correctly and the preceding page address code corresponds with the selected page while disregarding digitized groups of characters preceded by an incorrectly received start code and groups of characters preceded by a page address code other than that selected, R
reading device operable to read the digitized characters repeatedly from the memory device, and a character generator connected with the video circuit and being responsive to the digitized characters read by the reading device to provide character signals for visual display by the display device.
reading device operable to read the digitized characters repeatedly from the memory device, and a character generator connected with the video circuit and being responsive to the digitized characters read by the reading device to provide character signals for visual display by the display device.
17. A system according to claim 16 having a video switch between the character generator and the video circuit and arranged to provide a choice between display on the visual display of normal video signals alone, character signals alone, and character signals superimposed on normal video signals.
18. A television receiver system having a memory device, a clocking device for actuating the memory device, an input for a set of pages of information received at said input in the form of digitized characters in a repeated cycle the form of which is such that the digitized characters for the set of pages are received in groups of the characters, and the whole of the information for the set of pages is received during each occurrence of the cycle, each group as received being preceded by a clock run-in signal, to which the clocking device is responsive for synchronization, followed by a known start code correct receipt of which indicates integrity of reception and also followed by a page address code, variable selector means for selecting a page from the set of pages and routing a group of digitized characters to the memory device when the preceding start code is received correctly and the preceding page address code corresponds with the selected page while disregarding digitized groups of characters preceded by an incorrectly received start code and groups of characters preceded by a page address code other than that selected, a reading device operable to read the digitized characters repeatedly from the memory device, a character generator responsive to the digitized characters read by the reading device to provide output signals for visual display by an intensity modulated raster of the television reception type, and a second character generator responsive to the digitized characters, said second character generator being operable to provide character rounding bits for superposition on the visual display.
19. A system according to claim 18 in which the character generator is operable to generate main characters in an m x n (m - 1) x (n - 1) matrix form.
20. A television receiver system having a parallel binary digital memory device, a clocking device for actuating the memory device, an input for receiving a demodulated television signal carrying, during picture-free periods thereof, a set of pages of information in the form of serial binary digitized characters provided in a repeated cycle the form of which is such that the digitized characters for the set of pages are received in groups of the characters, which groups are received each in a different one of said periods and the whole of the information for the set of pages is received during each occurrence of the cycle, each group as received being preceded by a clock run-in signal, to which the clocking device is responsive for synchronization, followed by a known start code, selector means responsive to page address codes present in the cycle, for selecting a page from the set of pages and routing a group of digitized characters, with conversion from the serial binary form to the parallel binary form, to the memory device when the preceding start code is received and the preceding page address code corresponds with the selected page while disregarding digitized groups of characters preceded by a page address code other than that selected, a reading device, operable to read the digitized characters repeatedly from the memory device, a character generator responsive to the digitized characters read by the reading device to provide output signals for visual display, as characters, by an intensity modulated raster, together with or separately from picture signals carried by the said signal and an arrangement for optionally routing to the memory device alternative character information received over a separate data channel so that characters derived from the alternative character information can be displayed together with or separately from the said picture signals.
21. A television receiver system having a parallel binary digital memory device, a clocking device for actuating the memory device, an input for receiving a demodulated television signal carrying, during picture-free periods thereof, a set of pages of information in the form of serial binary digitized characters provided in a repeated cycle the form of which is such that the digitized characters for the set of pages are received in groups of the characters, which groups are received each in a different one of said periods and the whole of the information for the set of pages is received during each occurrence of the cycle, each group as received being preceded by a clock run-in signal, to which the clocking device is responsive for synchronization, followed by a known start code, selector means responsive to page address codes present in the cycle, for selecting a page from the set of pages and routing a group of digitized characters, with conversion from the serial binary form to the parallel binary form, to the memory device when the preceding start code is received and the preceding page address code corresponds with the selected page while disregarding digitized groups of characters preceded by a page address code other than that selected, a reading device operable to read the digitized characters repeatedly from the memory device, a character generator responsive to the digitized characters read by the reading device to provide character signals for visual display, as characters by an intensity modulated raster, a text adding device responsive to the picture signal component of the demodulated television signal and the character signals to produce a signal representing the picture signal with superimposed text and controller means operable to provide as required for display, the character signals alone, the said picture component alone, or the said picture signals together with characters.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB3620673A GB1486772A (en) | 1973-07-30 | 1973-07-30 | Television systems |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1044797A true CA1044797A (en) | 1978-12-19 |
Family
ID=10385959
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA205,846A Expired CA1044797A (en) | 1973-07-30 | 1974-07-29 | Television systems |
Country Status (6)
| Country | Link |
|---|---|
| JP (2) | JPS5072518A (en) |
| CA (1) | CA1044797A (en) |
| DE (1) | DE2435794C2 (en) |
| FR (1) | FR2239832A1 (en) |
| GB (1) | GB1486772A (en) |
| IT (1) | IT1017734B (en) |
Families Citing this family (13)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1478695A (en) * | 1974-09-26 | 1977-07-06 | Texas Instruments Ltd | Data handling apparatus |
| JPS51131223A (en) * | 1975-05-08 | 1976-11-15 | Nippon Telegr & Teleph Corp <Ntt> | Type printing control method for ink jet printer |
| GB1526232A (en) * | 1975-10-08 | 1978-09-27 | Texas Instruments Ltd | Digital data storage systems |
| US4025851A (en) * | 1975-11-28 | 1977-05-24 | A.C. Nielsen Company | Automatic monitor for programs broadcast |
| GB1568378A (en) * | 1976-01-30 | 1980-05-29 | Micro Consultants Ltd | Video processing system |
| DE2760395C2 (en) * | 1976-09-06 | 1988-02-25 | Etablissement Public De Diffusion Dit "Telediffusion De France", Montrouge, Fr | |
| JPS55156485A (en) * | 1979-05-23 | 1980-12-05 | Sony Corp | Character broadcast receiver |
| NL8002412A (en) * | 1980-04-25 | 1981-11-16 | Philips Nv | MUTUAL TRANSFER OF INFORMATION ABOUT A "LONG DISTANCE VIDEO INTERFACE" (LDVI) CABLE. |
| DE3047597C2 (en) * | 1980-12-17 | 1984-08-16 | Siemens AG, 1000 Berlin und 8000 München | Arrangement for distributing information and for quick and targeted finding of information units having an address part |
| JPS6145279A (en) * | 1984-08-09 | 1986-03-05 | 株式会社東芝 | Smoothing circuit |
| JPS61142591A (en) * | 1984-12-13 | 1986-06-30 | Toshiba Corp | Semiconductor storage device |
| US4953027A (en) * | 1989-04-24 | 1990-08-28 | Motorola Inc. | OSD in a TV receiver including a window, smoothing and edge enhancing |
| US5333135A (en) * | 1993-02-01 | 1994-07-26 | North American Philips Corporation | Identification of a data stream transmitted as a sequence of packets |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NL153347B (en) * | 1968-02-16 | 1977-05-16 | Philips Nv | DEVICE FOR DISPLAYING DIGITAL INFORMATION ON A TELEVISION SCREEN. |
| DE2058681C3 (en) * | 1970-11-28 | 1974-04-11 | Licentia Patent-Verwaltungs-Gmbh, 6000 Frankfurt | Device operating in television mode for sending, receiving and displaying coded information |
-
1973
- 1973-07-30 GB GB3620673A patent/GB1486772A/en not_active Expired
-
1974
- 1974-07-25 DE DE19742435794 patent/DE2435794C2/en not_active Expired
- 1974-07-29 FR FR7426210A patent/FR2239832A1/fr not_active Withdrawn
- 1974-07-29 CA CA205,846A patent/CA1044797A/en not_active Expired
- 1974-07-30 IT IT2574774A patent/IT1017734B/en active
- 1974-07-30 JP JP8859574A patent/JPS5072518A/ja active Pending
-
1982
- 1982-02-19 JP JP57026707A patent/JPS57159186A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| JPS57159186A (en) | 1982-10-01 |
| JPS5072518A (en) | 1975-06-16 |
| FR2239832A1 (en) | 1975-02-28 |
| DE2435794A1 (en) | 1975-03-13 |
| IT1017734B (en) | 1977-08-10 |
| GB1486772A (en) | 1977-09-21 |
| DE2435794C2 (en) | 1983-09-08 |
| AU7176874A (en) | 1976-01-29 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |
Effective date: 19951219 |