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`‘-V0 RLD [NTEILLECTUAL PRO PERTY ORGANIZATION
`International Bureau
`
`1'NTERNA'I'IONA.L APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TRE-ATY (PCT)
`
`(31) Imernatiunal Patent Clnssificnnun 3:
`.
`EHMN 71' 16, 7/64 '
`E (43) Lnternational Publication Date: 1:3 October 1981 (1110.31)
`
`(31) Intemational Ayplicafiou Number:
`PCTIUS81/00414 I
`(72) Inventors; and
`
`(11) International Publication Number: WO 31/02961
`
`i I
`
`(75) Inventors/Applicants (fbr U5’ oniy): CAMPBELL. John. E
`G. {US/US}; 601 West Northgate. Irving. TX T5062 §
`(US). SCHOENEBERGER Carl, F. {US/US]; 3032 f
`Christie Lane, Carrolltou. TX T300? (US). BUN- -
`DENS. Allan. B. [US!L'S}; 1331 Clear Crack Lane, '
`CanaUton.TX7500?{US).FOGLE.R.ichard.§r{.[US/ 3
`US}: 2013 Knoxville Drive. Bedtbrd, TX 76021 (US).
`=
`LEMB URG, John. R. [US/USS: 512 Lexington Lane, =
`
`Richardson, TX 75030 (US).
`
`(7-1) Agents :THUR_‘V[.4£‘1. Ronald. V. ct 31.: Hubbard. ThuI- '
`man. Turner. Tucker 8-: Glaser, 1200 North Dallas"
`B an}: Tower. LBJ E-‘rcaway as Preston Road. Dallas. TX
`75230 {US}.
`
`(22) International Filing Date:
`
`31 March 1931 61.03.81)
`
`I I ! S
`
`(31) Prioritzr A;I1Jlic:1tiou Number:
`
`135.98?
`
`5
`
`E
`E
`
`(31) Priority Date:
`
`31 ;\rIarcl:L 1980 01.03.80}
`
`(33) Priority Country:
`
`US
`
`(60) Parent Appficafion or Grant
`(63) Related by Continuation
`US
`
`135.93? (CIP)
`
`(71) Applicant o'er ail desfgnared S:a:as creep: US).-TOCDM.
`ENC. [US/-US]; P.O. Box 47066. Dallas. TX $324? 1
`(US).
`__
`3
`
`(31) Designated States: AT (European patent), CH (Eu:-o»
`pean gzatentl. DE (European patent), FR {European .
`patentl. GB [European p.-1Lent1.J'P. LU{European pa-
`tent). .\‘T_ {European patent). 35 {European parcnn.
`US.
`
`
`
`Published
`
`With £rI.'emarfor:at" sears}: region
`
`{:74} Title: ADDRESSAB LE CABLE TELEWSION CONTROL SYSTEM WITH VDEO FORMAT DAT.-X
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`

`
`(ST) Abstract
`
`.-‘Ln addressable cable television control system controls television program and data signal transmission from 3 cent.-_—.;_
`station (11) to :1 plurality of user stations. The dam signais include both control and text signals in video line format which are in.
`serted on the vertical interval of the television signals. thereby freeing all channels for transmission oiboth television and tier;
`signals. Moreover, fullehztnnel teletext data in video line format may be transmitted on dedicated next channels with the tnocii.
`iicrttion ofonly head end processors [16]. An intelligent converter {cl-0} at each remote user location uses the data signals to con.
`trol "access to the system on the basis ofchannel. tier ot'serv1‘ce. special event and program subject rn:1lter.The converter uses :1
`graphic: display generator (1 18) to generate display signals for the presentation ofthe text data on the television receiver (36
`and for the generation ofpredeterrnjrted messages for the viewer concerning access. emergencies and other functions. The con.
`verter processes vertical Interval text data and seiected fitll-channel text data. both transmitted in video line format. The {ca-.-.
`board of the subscriber (146. 168) provides a number of different functional inputs for the subscriber to interface with the
`stern. The converter (40) also includes apparatus for interfacing with two-way interactive data acquisition and control systems
`
`_
`
`FOR THE PURPOSES OFHVFORJHATION ONLY
`
`C odes used to icletttifys tates party to the PCT on the front pages ofpamphlets p ub lishing international appli-
`cations under the PCT.
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`M.’
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`GB
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`Australia
`B rezll
`Cetllnl Afritztn Republic
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`Cameroon
`G-errrttttw. Federal Republic of
`Denmark
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`Gabon
`United Kingdom
`Hungary
`Japan
`
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`Democratic P.-.ooie'i Re;-ublic ot‘I\'.or::t
`Liechtenstein
`Luatern bout;
`Monaco
`Madagascar
`M a.la\‘vi
`Netherlands
`Norway
`Romania
`Sweden
`Senegal
`Soviet Union
`Chad
`Togo
`United State! offitrneriea
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`

`
`‘W W”3‘)°l
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`PCTXUSBlf00~li-l
`
`ADDRESSABLE CABLE TELEVISION CONTROL SYSTEM WiT}-i
`
`VIDEO FORMAT DAT/-\ TRANSIN.-IISSION
`
`CROSS REFERENCE TO REI_.'~\TED APPLICATION
`
`This
`
`is
`
`a c.ontinuation-in~part application of our prior co-
`
`pending application, U.S. Serial No. 06,353,937,
`
`filed March 31, 1980.
`
`B.-3.CKGROL':\'D OF THE L\“."E:\‘TiO:\.’
`
`This invention relates to an addressable cable television control
`
`system. More particularly,
`
`the present
`
`invention relates to a cable
`
`television system having a multiple-function addressable converter and
`
`including data transmission in video format during the vertica interv.=_l
`
`of the video field or during substantially the entire video field.
`
`In recent years,
`
`the availability of cable television programs
`
`and services for
`
`the general public has expanded rapidly-
`
`Con‘:-
`
`munication satellites have enabled nationwide programming for a
`
`number of "super stations". Sophisticated two—way interactive cable
`
`communication systems have laid the groundwork for a wide spectrum
`
`of cable television and data communication services for the consuming
`
`public. After years of development, cable television systems have been
`
`or are now being installed in many major cities
`
`to provide the
`
`television consumer with a vast array of programming choices as well
`
`as many other services which can be utilized at home,
`
`such as
`
`shopping, banking and schooling. Other services provided by such
`
`‘systems incude home security monitoring, medical and emergency
`
`alert signaling and information retrieval.
`
`In order
`
`to provide these new services and programs in a
`
`systematic and efficient manner, generalized control
`
`systems are
`
`required which can supervise access to both one-way and two—v.-av
`
`3
`
`

`
`1'\..A.- l.a¢u1.fUU1-1-i-
`
`2
`
`sophisticated cable communication systems having different degrees of
`
`complexity. Control
`
`is required to differentiate and limit access on
`
`several bases,
`
`including different
`
`levels or
`
`tiers of subscribers to
`
`different television channels, and different programs and events on a
`
`given channel.
`
`In addition, for many subscribers it is desirable to be
`
`able to limit access to certain prbgrarns because of
`
`the program
`
`there are no cable systems having this
`Presently,
`subject matter.
`degree of sophistication in controlling program access.
`Even simpler
`conventional cable systems which provide for limiting program access
`
`must be two—way interactive systems requiring more complex and
`
`expensive equipment than one—vvay systems.
`
`Besides this problem of coordinating cable communications, the
`
`need for efficiency in
`
`the transmission of data has become in-
`
`creasingly apparent.
`
`Athough approximately 55 video and sound
`
`channels are presently available between the allocated teievision
`
`frequencies of 50 and ‘-500 megahertz,
`
`the varied types of possible
`
`cable television programming and data transmission services require
`
`the efficient utilization of
`
`these frequencies.
`
`For example, cable
`
`television programming includes movies, special events, news, con-
`
`sumer programming, community access and religious programming. An
`
`almost limitless range of data can be provided,
`
`including reports on
`
`stock and money markets, weather reports, airline schedules, shopping
`
`directories, entertainment schedules,
`
`traffic reports, home security
`
`data emergency and first aid information and unlimited library textual
`
`information. The possibility for cable system operators
`
`to lease
`
`available cable channels to private concerns
`
`for
`
`these and other
`
`services makes
`
`it
`
`imperative
`
`that cable transmission control be
`
`efficient and flexible.
`
`in order
`
`to effectively utilize the available
`
`portion of the electromagnetic spectrum for such a wide variety of
`
`programming and data transmission, the cable system should be able to
`process the data quickly and efficiently while using relatively simple
`
`and inexpensive equipment which is affordable to the general con»
`
`suming public.
`
`In the last few years, various experiments have been conducted
`
`regarding the transmission of data over the vertical blanking interval
`
`of"a normal teievision signal. This interval in the video signal occurs
`
`4
`
`

`
`W0 3””-'39“
`
`PCT/U581/0041-1
`
`60 times each second as the cathode ray tube beam sweeps from the
`bottom to the top of the TV screen and is relatively unused for the
`
`transmission of data. Some early systems such as that shown in U.S.
`
`Patent 3,769,579- issued on October 30, 1973, utilized the vertical
`
`interval for transmitting control signals to individual transponders at
`the subscriber
`locations. More
`recently,
`there has been exper-
`imentation with television broadcasting systems which transmit visual
`
`data on
`
`the vertical blanking interval,
`
`referred to as
`
`teletext
`
`text on suitably equipped
`for display as pages of
`transmission,
`television receivers. These experimental systems have generally been
`limited to over—the—air broadcasting of
`teletext
`transmissions for a
`
`for cable television
`single channel, and the necessary apparatus
`systems has been regarded as too complicated and expensive to be
`practical when compared to the high—speed transmission of compact
`data over a dedicated channel.
`
`it is desirable in many instances to dedicate _an entire television
`channel
`to the transmission of data rt-'.her_ than video signals.
`Prior
`art systems
`for dedicated data channels
`typically require special
`transmitters and receivers different from those used for
`the trans-
`mission of video signals in order to achieve the desired high baud (bits
`per second) rate to efficiently utilize the channel bandwidth.
`This
`
`special data transmission equipment has resulted in substantial cost
`
`and complexity, particularly at each remote user terminal where a
`different receiver is usually required for each dedicated data channel.
`A simple and inexpensive system for
`the high speed transmission of
`data on a dedicated data channel has been greatly needed.
`
`SUMMARY OF THE INVENTION
`
`invention provides a relatively inexpensive and
`The present
`simple cable television system having the capability of controlling
`access to a wide range of television program and data sign.-as while
`efficiently transmitting data signals
`in a video format during the
`vertical interval (VT) of each television program charinel. This V'l data
`not only provides control data for an intelligent converter
`unit, but
`also provides a substantial amount of textual data per channel
`for use
`either to provide additional data to supplement a channel
`television
`program or as a separate all
`textual and graphic channel.
`
`5
`
`

`
`“'0 31/02961
`
`PCT/U881/00414 '
`
`1.1
`
`The present
`
`invention includes an intelligent addressable con-
`
`verter designed to convert and descramble video for up to 55 CATV
`channels. For dual cable systems, an optional cable switch on the
`
`converter doubles the available number to H0 channels. The converter
`of the present invention receives control data which allows the system
`operator to control subscription television services on a per channel,
`per service tier, and per event basis.
`In addition,
`the system and
`converter of the present invention enables each subscriber to define
`his own level of required eligibility based on program subject matter.
`The system of
`the present
`invention also enables a com-
`plementary text channel to be transmitted on the vertical interval of
`‘each of the incoming video signals and to be decoded and displayed as
`an alternate channel
`to the video programming.
`The data for
`the
`complementary text channel
`is preferably displayed in a combination
`of text and graphics.
`This capability effectively adds 55 additional
`
`text channels for a wide spectrum of data—type information for the
`consumer. Thus, the present system provides ll!) independent channels
`of television program and text viewing in a one cable system and 220
`channels in two cable systems. Moreover the control system of the
`present invention, when used in conjunction with appropriate two-way
`interactive apparatus, provides a complete two~way interactive com-
`munication system including pay—per-view, home security, opinion
`polling, channel monitoring, information retrieval, and with additional
`equipment, energy management.
`
`Moreover, the present invention provides a relatively inexpen-
`sive and simple cable communication system having the capability of
`transmitting data signals in a video format over substantially the
`entire video field of selected television program channels.
`By
`transmitting data in the video format over
`these dedicated data
`channels,
`the present
`invention minimizes
`the need for
`special
`additional expensive equipment, particularly special data receiver
`equipment
`for
`each converter unit.
`Rather,
`each addressable
`converter of
`the present
`invention is readily adap_ted to receiving
`selected lines of data transmitted in video format without requiring
`additional expensive receiver equipment.
`
`invention, together
`For a better understanding of the present
`with other and further objects and features thereof, reference is made
`
`i< EA 3
`3 ',_‘
`02.3?!
`
`6
`
`

`
`W0 8l!O2961
`
`.
`
`PCWUS81/00-I14
`
`ioliowing description taken in
`to the
`companying drawings.
`
`connection with the ac-
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`a preferred
`FIGURE 1
`is
`a simpiified block diagram of
`embodiment of the addressable cable television control system of the
`present
`invention;
`
`FIGURE 2 is a block diagram of a preferred embodiment of the
`head end portion of the system shown in Figure 1;
`FIGURE 2A is a diagram showing the line layout of a video
`field according to the present invention;
`FIGURE .23 is a time-based diagram showing the video iine
`format of data transmission in accordance with the present invention; ,
`FIGURE 3
`is a block diagram of
`the programming control
`system shown in Figure 2;
`FIGURE it
`is a block diagram of the head end video processor
`shown in Figure 2;
`
`FIGURE 5 is a more detailed block diagram of the head end
`video processor of Figure F4;
`
`shown in Figure 6;
`
`FIGURE 8 is a block diagram of the VI data extractor unit
`shown in Figure 5;
`showing two
`and ID are schematic diagrams
`FIGURES 9
`preferred methods of connecting the converter of Figure 6 in a CATV
`system;
`
`FIGURE 11 is a schematic diagram showing the data format for
`the system of the present invention;
`FIGURE 12 is a flow diagram showing the operation of the
`converter shown in Figure 6;
`FIGURE 13 is' a top plan view of the l<eyboard.of the converter
`of Figure 6;
`
`FIGURE 14 is a diagram showing a video iayout for fuii—channel
`teletext data transmission in accordance with another embodiment of
`the present invention;
`
`0:.-pr
`,
`V-'-,.,,__ mi-U
`
`.
`‘.‘\»
`
`7
`
`

`
`W0 8I!02961
`
`PCTfUS81I004I~1
`
`FIGURE [5 is a block diagram for the preferred embodiment of
`FIGURE II: of the head end portion of the system shown in
`FIGURE
`1;
`
`5
`
`FIGURE 16 is a block diagram of the screen composition system
`and selective data retrieval system shown in FIGURE 15; and
`the
`FIGURE‘ 17
`is a flow diagram showing the operation of
`converter shown in FIGURE J6 operating in conjunction with the head
`end of FIGURE 15.
`
`DETAILED DESCRIPTION
`
`FIGURE 1 shows a simplified block diagram of a one—way cable
`television system l0 in accordance with the present invention. A head
`and station ll
`includes a central data system 12 utilizing a control
`computer which gathers data from a wide variety of sources and
`formats the data for
`transmission on video frequency channels. The
`central data control system preferably has a two—way interface link 13
`with a remote computer which may be used for central control and
`billing
`functions.
`The
`formatted data
`is
`then
`transmitted by
`communications link its
`to a television program processor I6 where it
`is incorporated into the vertical blanking intervals of video signals
`generated by a variety of television program sources.
`In addition, the
`data may be
`formatted for
`transmission in
`a
`separate channel
`dedicated only for
`the transmission of data.
`The dedicated data
`channel transmissions are connected over link 18 to a head end signal
`combiner 20 where they are combined with a plurality of video signals
`transmitted from television program systems 16 along transmission link
`22. The head end unit then transmits the combined cable television
`and data signal to remote subscribers. Normally, the signals are then
`transmittednthrough a cable network, referred to as a cable plant to
`a plurality of subscribers.
`
`'
`
`FIGURE l shows a single cable plant 30 servicing a plurality of
`cable television subscribers by way of a one-way data link 32.
`The
`transmitted signals are received by an addressable converter #0 on a
`one"—way data bus 32. Converter 40 then processes the data on line 38
`as determined by subscriber input
`34% for desired viewing on one or
`more television sets 36.
`
`8
`
`

`
`n-vuspu-.;u;
`
`f\_1‘iu_';o".uU.,J_.,.
`
`Referring now to FIGURE 2, one preferred embodiment of the
`
`data control system 12 and television program processor
`
`16 is shown
`
`in greater detail.
`
`This preferred embodiment which is shown in
`
`FIGURES 2 through 12 concerns a system which transmits data in the
`vertical
`interval of each video field. - Another preferred embodiment
`
`disclosing a full-channel data transmission system using a video format
`
`will be discussed thereafter.
`
`—
`
`As shown in FIGURE 2, a programming control system {PCS}
`50 generates a continuous stream of data that contains‘ a mixture of
`
`subscriber addressing signals and channel control signals.
`
`This data
`
`is transmitted to a plurality of head end video processors
`
`(H\/Pl 52
`
`and 53 for combining with video signals in a plurality
`
`of different
`
`channel frequencies. PCS 50 is also preferably connected by _a two-
`way data link to a remote computer
`for use in various
`conttol
`functions.
`
`:5; text formatter system 5!; receives data from a wide variety
`of‘ sources
`such as
`‘.\’eE.t§"I.er,
`nev.-s,
`stock and others which are
`
`formatted for video transmission and then selectively transmitted in
`
`text form to the plurality of HVP units 52, 53. The text forrnatter
`
`system 5!; preferably is comprised of a plurality of text forrnatters,
`
`each processing data from a text or graphics source.
`
`A variety of
`
`manufacturers produce‘ equipment for cable television digital channels
`
`which are easily adaptable to the present
`
`system. One source of
`
`suitable conventional
`L.I., N.Y.
`
`forrnatters is Video Data Systems, Happaque,
`
`Video signals are generated for
`
`input
`
`to each I-WP unit by
`
`conventional sources, either from local video input sources as shown
`
`for HVP unit 52 or satellite video input sources for HVP unit 53.
`
`In
`
`either_case,
`
`the signals are processed by a conventiona channel
`
`processor 56 having modulator and demodulator units and a standard
`
`head end processor. Each television channel is preferably processed at
`
`base band video for purposes to be explained later.
`
`The subscriber addressing and channel control data from PCS 50
`
`is input
`to I-l\/P 52 on line #1 where it
`is inserted in the vertical
`interval_of the video signal. The channel control data from PCS 50
`is processed at "l-NP 52 to generate scrambler signals, program
`
`identification signals, tier signals and eligibility code signals as will be
`
`9
`
`

`
`a
`
`I...-4.
`
`|.4\.aU.|..'U'U'-r.L-r
`
`discussed later.
`
`These signals are utilized by each subscriber‘s
`
`addressable converter #0 to determine the particular
`
`subscriber's
`
`authorization to receive each program and to control descrambling of
`the video signals.
`
`One of the text signals from text formatter 51% is also input to
`
`HVP 52 on line 39 to be inserted into the vertical interval of the video
`
`signal. Preferably, __a different type of textual data are inserted into
`the vertical intervallof each video channel so that a complementary
`text channel may be selected by each remote subscriber.
`
`10
`
`the base band-video output with
`HVP unit 52 then routes
`vertical interval data on line ~£M.'- to a standard head end modulator and
`
`processor
`
`in processing unit 56.
`
`From there,
`
`the signal
`
`is sent
`
`to
`
`master head end unit 20 where it is combined with signals from other
`
`channel processors to provide the total multiple channel CATV signal
`
`for output on line 21 to the cable plant. An FSK data modulator 58 is
`connected directly between PCS 50 and head end signal combiner 20
`line lS for transmission of data on dedicated data channels.
`
`In order to understand how a data signal is transmitted on the
`
`vertical interval of a television program signal, the vertical interval of
`
`Referring to
`television signal will be described.
`a conventional
`FIGURE 2A, each television signal
`is made up of a series of "lines"
`each of which represent the length of time required for the cathode
`
`ray tube of the television set to make one horizontal sweep across
`
`the
`
`screen. The number of horizontal lines required to cover the screen
`
`is called a field 700, and there are two interlocking fields, both having
`262.5 lines which together form a frame._ In conventional systems, 30
`frames are transmitted each s-econdto make up the television picture.
`
`15
`
`20
`
`25
`
`-Each time the cathode ray tube reaches the bottom of the screen it -
`rnust sweep diagonally upward to the top of the screen to begin a new
`
`30
`
`field." This time period 702 is referred to as the "vertical
`
`blanking
`
`‘_
`
`interval" or simply "vertical interval" and is normally
`
`approximately
`
`21 lines in length. The television picture 70!; begins at about line 21
`and extends to about line 261, but normally the picture is viewable on
`
`most television sets only between about
`
`lines 25 and 255.-
`
`35
`
`Although no television picture data is transmitted during the
`H
`vertical interval,
`the television industry has provided for a number of
`different types of control transmission on certain lines of the interval.
`
`10
`
`

`
`1'l..1.Fl..'Z}0l..rUU-l-1-k
`
`in most cases, the first nine lines of the vertical interval are used for
`
`equalizing and for vertical
`
`synchronization.
`
`Lines
`
`10
`
`to 15; are
`
`normally at black level to minimize picture interference on some sets.
`
`Thus, only lines 15 to 21 are available for data transmission. Lines 15
`
`and 16 have already been utilized at
`
`least experimentally for other
`
`Lines '19-21 are normally used for network control
`purposes.
`formation for transmission to the receiver sets.
`
`in—-
`
`Thus,
`
`lines 17' and 18 are the only ones which are presently
`
`available for vertical interval data transmission 710 using the invention
`
`of the present system.
`
`These two lines normally contain network
`
`testing data to determine proper reception by the head end system.
`
`Once the television signals have been received,
`
`lines 17 and 13 can be
`
`cleared for passing data to the converters using the present invention.
`It should be understood that if additional lines in the vertical interval
`
`they could also be used for data
`future,
`the
`are cleared in
`tiansrnission in accordance with the present
`invention.
`I
`Preferably,
`the present
`invention uses lines l7 and 18 of the
`vertical
`interval
`to transmit both the text data and the subscriber
`
`address and channel control data.
`
`In one field of a given frame lines
`
`l7 and I8 are used to transmit text data, and in the other frame
`
`field,
`
`the subscriber address and channel control data is projected on lines
`
`17 and 13. The present
`
`invention also uses line 10 which is at
`
`the
`
`black "zero" voltage
`
`level of
`
`each vertical
`
`interval
`
`for a DC
`
`reference level 712 for the data signals. This reference signal passes
`
`to the converter as part of the vertical
`
`interval where it is used as
`
`a reference level for data extraction. This procedure greatly enhances
`
`the accuracy of the data transmission by automatically compensating
`
`for any- DC level shift in the vertical interval portion of the television
`
`signal.
`
`Using the procedure described above an effective text charac-
`ter transfer rate of about 2&0 characters per second is achieved. This
`
`is a relatively slow rate compared to some other ‘methods of data
`transmission. However, since the text may be transmitted over all 55
`television program channels the total text available to the user is very
`
`substantial. Moreover, as previously mentioned, the present invention
`
`may include one or more dedicated channels for only text data
`
`transmission using the "line" or video format which will be described
`
`11
`
`

`
`- ~.-+1 -..«----van: uu—ra-r
`
`10
`
`more fully in FIGURES 2E and ii. By using most of the 525 lines of
`
`each television signal frame for text data transmission a vast quantity
`
`of text can be transmitted and received on a given channel using the
`
`transmitting and receiving- apparatus of
`
`the present system.
`
`special expensive data transmission or receiving equipment
`
`is
`
`No-
`
`re-
`
`quired.
`
`.,
`
`.
`
`A better understanding of the line or video format of the data
`
`used in the present invention may be obtained by reference to FIGURE
`
`2B, which shows a standard timing diagram for a single television line
`
`of the type shown in FIGURE 2A. This is a standard video line format
`
`in accordance with FCC or NTSC requirements. The amplitude of the
`
`video signal
`
`is measured in standard IRE units.
`
`15
`
`the video signal begins with a negative
`As shown in the figure,
`horizontal sync pulse 720 of about #0 IRE units. This pulse establishes
`the beginning point of the horizontal sweep of the cathode ray tube
`‘across the screen. Next, a color burst oscillating pulse F22 occurs
`which is normally used to synchronize color decoding circuitry in a
`television receiver.
`
`Data is encoded in the video scan line 725!» following the color‘
`burst signal 722 as shown in FIGURE 25.
`This
`line is normaliy
`
`composed of 92- bit intervals with each bit being identified as "1" with
`
`an amplitude level of 50 to 80 IRE units or "O", carrying an amplitude
`
`of approximately zero IRE units.
`
`In this manner, the standard analog
`
`video signal is replaced by a binary digital data packet 726 of 92 bits
`
`which is transmitted together with the horizontal sync pulse and color
`
`burst pulse, both of which are analog signals.
`
`Looking now at FIGURE 3, the programming control system 50-
`
`is shown in greater detail.
`
`The heart of PCS 50 is a sophisticated
`
`control computer, having both a random access memory and a read-
`
`only'rnemory.
`
`Computer 60 is preferably a conventional general
`
`purpose rninicornputer utilizing a central data system. Computer 60
`
`may be controlled by a conventional system operator console 62, a red
`time clock El; and external data links 66 including a two—way interface
`with another remote computer for central control. Control computer
`Eli
`is also connected to magnetic storage devices such as a cartridge
`ta-pe data 'storage unit 68 and a
`floppy disk subsystem 70 com-
`municating with control computer 60 over two-way data links 72 and
`
`12
`
`

`
`i‘L.J..p'Ll.‘_‘(J1.fUU-I-.I.-r
`
`ll
`
`71.! respectively. Other outputs to conventional units such as remote
`
`terminal 76 and printer 78 are optional.
`
`_ One preferred embodiment. of control computer 60 comprises a
`
`rack—mounted Hevvlett-Packard 1000
`
`rninicomputer
`
`system having
`
`standard operating system software. The computer may also include
`
`application programs allowing it
`
`to interface with two—way data
`
`acquisition and control systems.
`
`This interface is preferably carried
`
`out by communications with the home terminal shown in FIGURE l0.
`
`The head end video processor unit 52 of FIGURE 2 is shown in
`
`A digital control and timing unit 30
`in FIGURE 4.
`more detail
`receives the text data from text forrnatter 55% on line 39 and the
`
`subscriber addressing and channel control data from PCS 50 o_n line til
`
`and processes it
`
`for
`
`insertion in the vertical
`
`interval of the video
`
`channels. The data on line lél
`
`loops through unit 80 and back out on
`
`line £52 to the next digital control and timing unit. The base band video
`signal-is input on line ’—'3
`to a video- vertical
`interval processing unit
`32 where it is processed for insertion of the subscriber addressing and
`
`As
`channel control data from unit 80 via two—way data link
`previously described,
`the data is preferably inserted on two lines of
`each vertical
`interval
`and then directed to a conventional video
`
`_scrambler 86. The resulting video signal which has been loaded with
`
`data and scramblediis then connected to the standard head-end
`
`processor 56 shown in FIGURE 2.
`
`Referring now to FIGURE 5, the head end video processor 52 is
`
`shown in even greater detail. The digital control and timing unit
`80
`includes a data formatter 83, a. scirarnbler controller 90, a sample and
`hold unit 92 and a timing signal generator 9#.
`The video
`vertical
`
`interval processing unit 82 includes a sync extractor 96 and
`
`a video
`
`switch unit 93.
`is input on line 43 to the sample and hold unit
`The video signal
`92, the sync extractor 96 and the video switches 98. The text data
`
`is input
`to the data formatter 88 on line 39 and the subscriber and
`control data is input on line 1:1 to data formatter 38 and output on line
`3:2. The sync extractor unit 96 divides out the horizontal and vertical
`sync signals from the video signal and directs them to the timing
`signal generator on line 85.
`Timing signal generator 91; counts the
`
`lines of the vertical interval of each field and outputs enabling signals
`
`El.
`
`the appropriate time.
`
`13
`
`

`
`""""““‘””‘
`
`l"'L.J./U::'dUUU—l-i-l-
`
`l2
`
`is output to sample and hold unit 92
`A reference enable signal
`on line 95 when "line 10"
`in each vertical
`interval
`is detected
`
`representing the black "zero" level which is used asthe DC reference
`
`level. The sample and hold unit
`
`then outputs a DC reference signal
`
`on line 93 to the data formatter so that the incoming data or text can
`
`be- properly positioned relative to ''line ID" of the vertical
`
`interval.
`
`The properly formatted data is then output to video switches 98 to
`
`await
`
`transmission at the proper time in the vertical
`
`interval.
`
`when timing signal generator 91; reaches "line l7” in the vertical
`
`interval, a data enable signal is output on line 83 to the video switches
`
`98. Upon receipt of the data enable signal, video switches 93 turn off
`
`the video input and turn on the data input which is passed through on
`
`line 81 to the video scrambler unit 36. At
`
`the same time, a scramble
`
`disable timing signal is transmitted from data iormatter 38 on line 89
`
`t_c_>_ the scrambler controller 90 which in turn outputs a scramble disable
`
`s_ignal on line 8}’.
`
`This signal enables the data on line Si
`
`to pass
`
`through the video scrambler
`
`and out on line
`
`l-I-L: without being
`
`scrambled. When timing signal generator detects the end of "line I3"
`
`of the vertical interval, a data disable signal is directed via line 33 to
`
`the video switches 93 which turn off the data line and turns on the
`
`is
`.-\t_ the same time, a scramble enable timing signal
`video line.
`directed on line 89 to the scrambler controller which transmits a
`
`scramble enable signal to the video scrambler via line 87. This signal
`
`enables video scrambler 86 so that the video signals coming in on line
`
`31 will be scrambled before being transmitted on line M.
`
`It should also be noted_ that scrambler controller unit 90 outputs
`
`a scramblefdescrambie timing signal on line?! to the data formatter
`
`"83. This signal is added to the data which is sent to video switches 98'
`
`30
`
`‘for transmission. This signal is utilized by the converter #0 as will be
`discussed later_to control the descrarnbling oi the video signal at the
`converter.
`
`Referring now to FIGURE 6, the addressable converter unit #0
`of FIGURE 1
`is
`shown in greater detail.
`The converter, under
`direction of converter
`control logic, processes the RF data—loaded
`television signals from combined video output
`line 21 of head and
`
`signal combiner 20 and provides video and audio output
`
`for
`
`a
`
`14
`
`

`
`"V U1--‘V-‘JUL
`
`l’l..1H.'CC$l.-’UU~+l.-l-
`
`13
`
`television set, preferably on
`
`channels
`
`3 or
`
`ii-.
`
`In a two—way
`
`interactive system the RF input
`
`to the converter 3&0 also includes
`
`data. from a two-way home terminal as will be shown and discussed
`
`in conne