Ciciora, Sgrignoli, Thomas: Introduction to Teletext and Viewdata
`
`235
`
`AN INTRODUCTION TO TELETEXT AND VIEWDATA WITH COMMENTS ON COMPATIBILITY
`
`Walter Ciciora
`
`Gary Sgrignoli
`William Thomas
`
`Zenith Radio Corporation
`1000 Milwaukee Avenue
`
`Glenview, Illinois 60025
`
`ABSTRACT
`T-T_"T_'
`two parts,
`This paper is written in
`Part I
`is intended to be an introduction to
`teletext
`and
`viewdata
`for
`readers, with
`limited exposure to these topics.
`Part
`I
`also serves
`as
`an
`introduction to
`the
`Special Issue of
`the IEEE Transactions
`on
`Consumer Electronics
`devoted
`to Consumer
`Text Display Systems.
`compatibi1ity
`the
`Part II comments on
`question with
`emphasis on page format.
`A
`24 row by 40 character format is
`advocated
`and supported.
`
`(FOR INFORMATION RETRIEVAL):
`KEYWORDS
`Teletext, Viewdata, Videotex, Videotext,
`Consumer
`Text
`Display,
`Television,
`Telephone,
`Information
`Retrieval,
`Terminals.
`
`programs
`contains a computer which can run
`The
`two
`transmitted
`over
`the
`system.
`SYstems Can be designed t°
`share most
`°f
`the Large §Ca1e lhtegration (LS1) Circuits-
`In
`Particular,
`the
`page Bandom Access
`flemory (RAM),
`the gathode gay Tube
`(CRT)
`controller.
`and
`the
`character 5ead9_n1y
`flemory (ROM) are shared.
`the
`details,
`without getting
`into
`history of teletext and viewdata is briefly
`as follows. Teletext arose as an extension
`of efforts in British televison to transmit
`signals within
`the
`television network
`plant.
`An intermediate goal was Captioning
`{or the Qeaf
`(CFD). Viewdata arose out
`of
`the
`disappointment
`over picture
`phone
`service. Besides showing pictures, picture
`phone was
`thought
`to
`be
`useful
`for
`transmitting .text
`and diagrams.
`viewdata
`preserves the latter
`two
`functions while
`reducing
`the
`required channel
`bandwidth
`down to that of the twisted telephone pair.
`Fortunately for all concerned -— especially
`the consumer -— the efforts
`of
`these
`two
`groups were merged along somewhat parallel
`paths. while in some
`respects‘ these
`two
`systems
`tend
`to compete,
`in most respects
`they are complementary.
`v
`contain fundamental
`2
`and
`Figures
`is
`signal
`In
`teletext
`the digital
`teletext
`and
`viewdata.
`definitions
`embedded in Video Waveforms as an ahCi11arY
`viewdata have become generic
`Teletext
`and
`signal.
`The
`system
`is
`usually
`terms; as such they may be spelled with
`a
`n0n-interaCtiVe- That is.
`the user
`does
`lower
`case
`letter.
`videotex is somewhat
`not
`control what
`is transmitted down the
`synonymous with
`viewdata.
`Individual
`Channe1- Rather the Pages Of
`ihf°rmati°h
`organizations
`have
`come up with their own
`are cyclically repeated and the receiver
`brand names for their services.
`grabs a page as it comes by and
`stores
`it
`things
`Teletext and viewdata have many
`in
`a
`local
`page memory.
`The Size Of
`the
`in common. Both are intended primarily for
`data base is moderate,
`numbering
`several
`display
`on
`consumer
`co1or
`te1ev1s1on
`hundred pages.
`The number of pages present
`receivers
`have
`been
`used
`with
`but
`affects the access time since all the Pages
`monochrome
`receivers, color or monochorome
`must
`be cyclically repeated.
`To give some
`video monitors, and to drive page printers.
`feel for the magnitude of
`the access
`time,
`Text augmented with simple graphics present
`consider the British teletext system.
`The
`a message which is transmitted in a highly
`maximum number
`of
`pages is eight hundred
`efficient digital form.
`The information is
`due to the error protection used in coding
`packaged in fundamental units called pages.
`page -numbers.
`The maximum number of rows
`The
`page
`format
`is the number of rows of
`in a page is twenty
`four.
`Two
`of
`these
`characters and the number of characters per
`rows
`are transmitted in every field of
`the
`row. Usually the page format is
`identical
`television signal.
`Thus in a
`truely full
`for
`the
`two
`systems
`in a given country.
`system of
`eight
`hundred
`pages each with
`The terminals which display the message may
`twenty four rows,
`9,600
`fields would
`be
`be simple or intelligent.
`The latter would
`required.
`In
`the British fifty cycle
`be
`capable
`of
`some processing of
`the
`sYstem. One hundred lines 05 teletext data
`information.
`the
`limit,
`the terminal
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`Page 1
`Page 1
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`PART I
`
`INTRODUCTION
`
`1
`of
`
`In
`
`

`
`236
`
`IEEE Transactions on Consumer Electronics, Vol. CE-25, No. 3, July 1979
`
`is
`
`each second so one minute and thirty
`occur
`seconds
`would
`be
`required
`per
`six
`of
`repetition
`all
`rows_
`This
`an
`absolute and very unrealistic worst
`case
`situation.
`Firstly,
`average
`access time
`for a given loading of the system would
`be
`half
`the maximum. Secondly eight hundred
`pages are rarely sent. But most
`important
`of all, sensible page design involves many
`blank rows- Thus if the system is
`loaded
`with two hundred pages with thirty percent
`blank rows, average
`access
`time will
`be
`eight
`seconds.
`The French Antiope system
`has carriage return, line feed, and
`cursor
`controls.
`Thus
`in addition to being able
`to skip blank
`lines
`it
`can
`skip blank
`characters within lines
`thus speeding up
`through-put and reducing access time.
`Teletext pages are
`sometimes
`compared
`to newspapers while Viewdata
`pages
`are
`sometimes compared with magazines or books.
`This analogy implies that users will
`turn
`to
`teletext
`for perishable
`information.
`This information will be of a newsy nature,
`changed often within a given day,
`it will
`also be information of wide appeal
`intended
`for
`a mass
`auoienoe_
`In contrast,
`this
`analogy
`sees Viewdata
`pages
`as
`being
`changed
`less
`often
`and/or
`containing
`information of more
`specialized interest,
`appealing to smaller
`numbers
`of
`users_
`This analogy has value
`if
`not
`taken
`too
`far.
`There
`are
`good
`reasons
`for
`interchanging
`these
`functions
`between
`teletext
`and viewdata. Most probably, all
`permutations
`and
`combinations
`of
`applications will
`be tried and the market
`place will decide which
`survives_
`It
`is
`too
`early to say where which information
`will go,
`analog
`fact
`in
`are
`Teletext signals
`representations of digital bits.
`A one bit
`analog
`to digital converter is required to
`make
`the
`transition
`from
`the
`analog
`television
`signal
`to
`the
`digital
`signal—handling circuits. But this is
`not
`simply
`a
`level slicer, This circuit most
`be
`an
`adaptive
`system capable
`of
`accomodating the kinds of nasty things that
`happen to television signals between studio
`generation and
`second detection in the
`receiver.
`In fact,
`this circuit
`is
`the
`most difficult
`to design and has been the
`source of most of the trouble in
`currently
`available chip sets for teletext,
`It is an
`analog
`circuit
`rather
`than a digital
`circuit.
`usually
`is
`base
`teletext data
`The
`on
`a menu basis. Certain pages
`organized
`contain tables of contents (menus) for
`the
`data base. Location of the desired data is
`usually very direct.
`In contrast, Viewdata
`data bases involve trees where
`pages
`lead
`on to other pages in long strings with many
`branches,
`A major challenge in organizing
`Viewdata data bases is to insure
`that
`the
`user does not get lost or frustrated by the
`process
`of
`searching,
`The
`information
`grovider (IP) must design his "data
`base
`with
`a great deal of accomodation of the
`mental process he believes his
`user will
`employ in searching for information.
`
`signals,
`teletext
`to
`contrast
`In
`bandwidth
`audio
`are
`signals
`Viewdata
`They are usually transmitted over
`signals.
`lines
`but
`any
`audio
`bandwith
`telephone
`channel can be
`used.
`Very
`conveniently,
`these
`signals
`can
`be preserved on audio
`recording devices.
`Viewdata
`systems
`are
`usually somewhat interactive in that pages
`do not come unless
`requested.
`The data
`bases
`are
`large
`and
`are
`fundamentally
`unlimited
`in size.
`Access
`is
`for all
`Practical
`purposes
`instantaneous.
`Data
`starts flowing almost
`immediately.
`while
`it
`takes a few seconds to fill a page,
`the
`lines appear as
`received
`and at
`a
`rate
`faster
`than
`reading speed.
`Thus the user
`is
`not waiting
`but
`reading
`almost
`immediately.
`The
`interface
`between
`the
`analog signal
`transmission channel and
`the
`digital
`logic
`is via a modem. Modem is a
`contraction of
`the words modulator
`and
`demodulator.
`access time can be reduced by
`Teletext
`using more lines out of the
`video
`signal.
`In
`the
`limit all lines in the television
`signal Can
`be
`Used-
`Thus
`We must
`distinguish
`between
`instantaneous
`bit
`transmission rate and average or effective
`bit
`transmission rate.
`In
`the British
`sYstem:
`teletext has an
`instantaneous bit
`transmission
`rate of 6.9 Mbits/sec.. This
`means that during the
`time
`that data
`is
`a
`sent:
`it
`is
`sent
`at
`fate
`05
`5-9
`Mbits/seC- When it is not being sent:
`the
`rate
`is
`0 Mbits/seC-
`The
`aVerage
`er
`effective bit
`transmission
`rate
`is
`the
`Weighted
`aVerage Of
`these fateso
`If this
`rate is transmitted on
`two
`of
`their
`625
`lines
`the
`effective bit transmission rate
`is 2/625 th of this times the fraction of a
`horizontal line time occupied by
`the data
`signal,
`i.e.
`0.81.
`The
`product
`is 18
`Kbits/sec.
`course
`if all
`available
`Of
`lines
`are
`filled with data,
`the effective
`bit
`transmission
`rate
`is
`just
`the
`instantaneous
`rate times the data fraction
`times
`the
`fraction of
`active
`lines
`or
`(6.9Mbits/sec)
`x
`(0.81)
`x
`(525/625)
`=
`5.2Mbits/sec.
`The
`use
`of all
`lines
`is
`possible on cable systems. private systems.
`and after hours on public systems.
`The
`latter
`concept gives teletext the
`ability to transmit
`tremendous quantities
`of
`specialized information after
`normal
`broadcast hours. when all available
`lines
`are
`used.
`aPPf°ximateiY 575 are emP1°Yed-
`Thus in one frame 23.96 pages can be
`sent.
`This Works out
`t0 413121500 Pages Pet h°Ut-
`The British Page
`number
`has a time Code
`associated
`with
`it-
`An
`intelligent
`terminal Can
`be Ptegtamed
`t° 1°°k 5°? a
`given page
`number at
`a given
`time
`and
`record
`the
`Page-
`The design
`0f
`the
`terminal ”°“1d determine
`he" manY Pages
`could
`be
`fetched after hours for use the
`next m°tning-
`teieVisi°n
`Teletext Can be applied t°
`signals of many forms:
`broadcast, consumer
`Cable.
`Private
`cable,
`and Multipoint
`Qistribution Service
`(MDS)-
`MES
`is
`a
`non—directionaI
`microwave
`transmission
`service.
`MDS
`operators
`are
`common
`
`PMC Exhibit 2063
`PMC Exhibit 2063
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`

`
`C iciora. Sgrignoli, Thomas: Introduction to Teletext and Viewdata
`
`237
`
`can
`these =services
`of
`Some
`carriers.
`themselves
`because
`support
`economically
`have at least some
`they are private
`and
`control
`over
`their
`signal distribution.
`Others,
`even
`the
`overnight
`broadcast
`service,
`can
`be made
`to
`pay
`through
`encryption.
`The digital nature of
`the
`information makes
`it
`‘very
`amenable
`to
`encryption techniques.
`Then the decoding
`equipment
`is
`the
`sold
`algorithm and /or
`enciphered
`data
`is
`product
`and
`the
`distributed free.
`signal
`viewdata terminals display the
`received.
`The usual method of use is for
`the terminal to
`request
`pages which
`are
`then transmitted,
`received and displayed.
`But
`if instead the signal source
`transmits
`a stream of pages with pauses between them,
`the viewdata terminal responds accordingly.
`This
`non—interactive
`application
`of
`viewdata is amenable to either
`a
`teletext
`like distribution of
`information in cyclic
`fashion with
`local
`page
`grabbing
`or
`a
`continuous
`pass
`through of new pages.
`As
`such,
`gubsidiary
`gommunication
`guthorization
`(SCA)
`subchannels
`on
`commercial
`FM stations
`be
`used
`to
`can
`distribute data. Ordinary audio recordings
`on disc or tape can carry the signal for a
`viewdata receiver.
`to
`available
`A
`significant option
`viewdata
`but
`not
`teletext
`is
`source
`processing of the data.
`This option has
`not
`been implemented in the British system
`but exists none the less. Preprocessing of
`data in the data base computer would
`allow
`other means
`of accessing data besides the
`tree search method. Cross referencing and
`other data
`base management
`techniques are
`possible. These approaches make more sense
`in a professional or business
`application
`of
`viewdata
`where
`the user
`is more
`sophisticated and
`trainable.
`The
`tree
`search
`method
`easy
`to use albeit
`is
`inefficient.
`It places
`the
`burden
`for
`careful
`design on
`the
`IP. However, its
`simplicity of
`use
`and
`the
`low cost
`of
`viewdata
`has made possible "time sharing
`for everyman".
`clock
`a
`of
`consist
`Teletext signals
`run—in burst,
`a
`framing code, a preamble
`and ASCII-like
`code.
`(ASCII
`=
`flmerican
`§tandard gode for Information Interchange).
`The
`clock
`run—in— burst
`is -a
`series of
`alternate logic ones and
`logic
`zeroes
`to
`allow the phase locked loop to acquire lock
`to the system clock.
`The framing code is a
`unique
`series
`of
`logic
`ones
`and
`logic
`zeroes which permit identification of which
`bit belongs to which logic word.
`In
`the
`British
`teletext
`system,
`the
`preamble
`contains
`information on which
`page
`and
`which row is being transmitted. Additional
`information about
`the way in which the data
`which
`follows
`is
`to
`be handled is also
`included.
`The Antiope
`system includes
`source
`identifier,
`continuity index
`and
`format
`specifier
`in the
`preamble.
`The
`preamble
`code
`is usually protected,
`at
`least
`partially,
`with
`Hamming
`error
`detection/correction
`techniques.
`The
`actual data which makes
`up
`the
`is
`
`page
`
`transmitted in a variation of ASCII.
`viewdata signals are of an asynchronous
`nature
`similar
`to teletype signals.
`They
`contain a start bit and a stop bit.
`Clock
`run-in
`and
`framing
`code
`are
`thus
`unnecessary.
`The bits are modulated onto
`an
`audio frequency carrier using Erequency
`§hift geying (FSK) modulation
`techniques.
`Movement
`about
`the page can be directed by
`the
`use
`of
`the
`usual
`terminal
`cursor
`controls.
`Thus overwriting, back spacing,
`tabulating, etc. are available techniques.
`
`GRAPHICS
`
`been
`have
`Two approaches to graphics
`proposed.
`The British and French systems
`use
`a
`form of graphics
`called
`mosaic
`graphics while the Canadian Telidon system
`employs geometeric graphics.
`the
`approach,
`In the mosaic graphics
`Each
`is constructed out of elements.
`page
`element
`consists
`of
`six
`subelements
`arranged
`into a
`two
`column by three row
`matrix.
`There
`are
`sixty four possible
`patterns
`of
`this
`six subelement matrix.
`3.
`See Figure
`There
`is
`a
`one
`to one
`correspondence
`between
`the
`location of
`graphic elements on a page of graphics
`and
`the
`location of
`characters
`on a page of
`text. This,
`in fact,
`is the beauty of this
`approach.
`The graphic
`character
`code
`is
`stored
`in
`the same page RAM as text code.
`The graphics are created by simply
`reading
`out
`of
`a graphics
`ROM
`rather
`than a
`character
`ROM .
`Very
`little additional
`circuitry
`is
`required to achieve
`this
`graphics
`capability.
`Graphics mode
`and
`text mode
`can
`be mixed in the same page.
`This
`is efficient
`from
`an
`equipment
`standpoint.
`The resolution is, of course,
`coarse.
`In graphics mode,
`twice the number
`of columns and three times
`the
`number
`of
`rows
`are
`available as in text mode. Thus
`graphics resolution in a
`forty character,
`twenty
`four row system is 80 columns by 72
`rows. while this level
`of
`resolution is
`limited,
`surprising
`results
`can
`be
`4
`obtained.
`See figures
`through
`9.
`It
`must
`be
`remembered that the object
`is not
`to transmit photos
`or
`a
`facsimile.
`The
`object
`is to add interest to the appearance
`of
`pages
`and
`to present simple graphics.
`This is to be
`accomplished at
`a minimal
`cost
`premium.
`The concept of cost/benefit
`ratio analysis
`applies.
`Very
`little
`additional
`cost
`has yielded substantial
`benefit.
`Systems have been developed which
`allow television cameras to be
`focused on
`hand
`drawn graphics
`or photographs.
`The
`camera inputs
`its
`signal
`to a
`computer
`which
`generates
`the
`appropriate
`code.
`Minor human touch up can sometimes
`improve
`the result.
`The Telidon approach to graphics allows
`future
`evolution.
`A
`high
`level
`for
`computer language defines the picture with
`Picture Description Instructions
`(PDI).
`focal
`computing
`power
`implements
`an
`interpreter
`program which
`expands
`this
`highly compact
`code
`into the
`individual
`bits
`which
`load
`the
`page
`RAM.
`The
`
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`Ciciora, Sgrignoli, Thomas: Introduction to Teletext and Viewdata
`
`239
`
`can
`important point here is that the PDI's
`be
`converted
`into a
`level of resolution
`appropriate
`for
`the display.
`If
`the
`display is
`a consumer color TV, a certain
`level of
`resolution is useful, more
`is
`wasteful,
`less does not use the display to
`full
`advantage.
`If
`the display is
`a
`thousand
`line monitor,
`the PDI's will be
`converted to a higher
`resolution picture.
`If
`an
`inexpensive
`terminal
`is required,
`even mosaic
`level
`graphics
`could
`be
`realized.
`of course a mosaic picture from
`PDI's will be more expensive than a mosaic
`picture
`from a mosaic system because the
`PDI's must be interpreted.
`
`EQUIPMENT OPTIONS
`
`of possible
`number
`There are a large
`configurations.
`The
`receiving equipment
`three most commonly considered are consumer
`color
`television
`built-ins,
`set—top
`adapters and special terminals.
`Built—ins
`provide
`the best possible
`display.
`To fully appreciate this, we must
`remember that what appears on the screen is
`synthetic video.
`It must
`be
`emphasized
`that the video is synthesized locally —~ in
`the
`adapted
`receiver.
`This
`takes place
`after the filtering and distorting effects
`of
`the
`antenna,
`tuner,
`IF, detector and
`video circuits.
`The CRT's Red,Blue,
`and
`green
`electron guns
`are d?ivefi directly
`(REG drive) to realize the
`full
`level -of
`sharpness
`of the picture tube.
`The colors
`are the most highly saturated possible.
`Either
`primaries,
`red,
`blue,
`green
`or
`secondaries, magenta,
`cyan,
`yellow
`are
`displayed
`(along with white and black)
`to
`the limits
`of
`the picture tube's
`color
`capability.
`Very
`significantly,
`color
`dot
`subcarrier
`crawl
`is
`absent.
`Also
`missing
`is any evidence of receiver noise.
`Misregistration
`between
`chroma
`and
`luminance
`images
`does not exist. And the
`cross stimulation of
`chroma
`or
`luminance
`channels
`is
`impossible.
`There
`are
`no
`ghosts in the displayed image.
`If
`signal
`reception problems
`occur
`such
`as signal
`ghosts or low signal
`to noise
`ratio,
`the
`result is still a perfect image.
`The image
`is just incorrect!
`The set-top adapter is a less expensive
`means of entry if the user has no desire to
`purchase
`another
`color
`receiver.
`The
`set—top adapter especially makes
`sense
`if
`it
`does other
`things
`such as unscramble
`subscription
`television,
`tune
`cable
`television channels, or decode the Captions
`For
`the Deaf
`service.
`But
`there
`are
`performance
`compromises.
`The
`optimum
`handling
`of
`these
`compromises makes the
`design of
`set-top
`adapter
`a
`more
`a
`difficult
`challenge
`than the design of a
`buit-in. Sadly,
`the goal of this design is
`to make a picture no worse
`than
`normal
`video.
`Better
`is out of reach. This is
`because the synthesis of the video is
`done
`before
`the
`color
`receiver rather than in
`it.
`The synthesized video must
`then be
`chroma encoded and modulated so it can make
`its way
`into the .receiver just like any
`
`the
`other color television signal. All of
`color
`compromises
`made
`to allow NTSC
`signal.
`television to exist apply to this
`There may
`someday be jacks on the back of
`color receivers to allow direct
`entry of
`the
`video
`signal.
`But
`the fact is,
`that
`there are not
`large numbers
`of
`these
`now
`nor will there be soon. Composite video is
`still
`NTSC video
`and thus does not solve
`most of the problems. Separate
`RBG
`jacks
`are
`needed
`if
`set—top
`performance is to
`equal built-in performance. But these
`are
`not present realities.
`Even if they become
`available,
`the cost of a new RBG jacked set
`plus set-top adapter would still exceed the
`cost of a built-in and the latter is a much
`neater
`package.
`In
`spite
`of
`the
`compromises,
`the antenna
`terminal
`set-top
`adapter will
`be
`an
`important product.
`Clever
`and
`innovative design can
`take
`advantage of the locally-synthesized—video
`nature of teletext and viewdata.
`The
`key
`is
`to
`synthesize
`the
`video
`in a manner
`appropriate for
`the
`application. Merely
`installing
`circuits
`designed
`for
`the
`built-in application into set—top
`adapters
`will yield suboptimal results. whereas the
`set—top
`adapter is an adequate realization
`of teletext and viewdata,
`true comparative
`advantage will
`accrue to the innovator as
`contrasted to the follower.
`no
`either
`Special
`terminals
`with
`de—emphasized
`television
`reception
`or
`television reception ability make sense for
`business
`applications
`or where
`conflict
`between
`the
`television
`and
`the
`text
`applications of the equipment
`are
`likely.
`The
`interactive nature
`of viewdata makes
`
`natural.
`viewing
`screen close—up
`small
`This is especially true if the terminal has
`an alphanumeric keyboard rather than just a
`numeric keypad. The non—interactive nature
`of teletext makes easy chair remote control
`of large screen television appealing.
`
`PART II
`
`LEVELS QE COMPATIBILITY
`
`To the extent that compatibility can be
`fostered,
`economies
`of
`scale
`can
`be
`achieved. This is particularly important
`in a new and growing technology, especially
`one which
`has
`chicken and egg problems.
`Except for pioneers, IP's can
`be
`expected
`to
`be
`reluctant
`to
`invest until
`the
`receiver population reaches
`a
`certain
`threshold
`level.
`Semiconductor
`and
`equipment makers will want
`to see a minimum
`level
`of
`software
`before
`they will
`participate
`in
`more
`than a
`token or
`defensive manner. Less expensive hardware
`on
`both
`the originating end
`and
`the
`receiving end will lower
`these
`thresholds
`by
`minimizing
`the
`risks.
`wider
`applicability of this hardware will
`cause
`the
`learning curves
`to be traversed more
`rapidly.
`There
`seems
`to
`be
`little
`disagreement
`about
`the desirability of
`
`PMC Exhibit 2063
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`

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`

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`Ciciora, Sgrignoli, Thomas: Introduction to Teletext and Viewdata
`
`24]
`
`The problem is in deciding
`compatibility.
`who is incompatible!
`
`THREE LEVELS
`
`of
`levels
`three distinct
`are
`There
`the
`if
`to
`Consider
`compatibility
`compatibility question is to be understood.
`They
`are:
`Language,
`Page Format,
`and
`Signal Format.
`The distinguishing factor
`is whether
`human intervention is required
`to overcome a lack of compatibility. Human
`intervention is
`both
`expensive
`and
`an
`on-going expense.
`It must be avoided if at
`all possible.
`
`LANGUAGE
`
`.
`The first level of compatibility is the
`easiest
`to dispose of.
`Human intervention
`is obviously required if pages of text
`are
`in another
`language.
`Perhaps
`some
`day
`computers
`will
`translate
`language
`effectively enough
`to be
`considered for
`international teletext
`and viewdata use.
`But
`for
`now,
`human
`intervention is
`the
`required. Fortunately,
`industrialized
`world
`has
`a
`large population of people
`speaking a mostly common language.
`It
`is
`most
`important
`to foster compatibility in
`areas where this language is shared.
`Once
`the
`development
`of an economically active
`system has been accomplished,
`its extension
`to other
`languages will
`rapidly
`and
`inexpensively take place.
`t0 the
`There
`is an amelidrating asPeCt
`language compatibility question.
`Some have
`argued
`that
`the m°st Valuable
`data
`on
`available
`teletext
`and
`viewdata
`is
`statistical or scheduling data.
`Financial
`and business data are the prime examples.
`This
`emphasis
`on
`numerical
`data
`is
`especially
`prevalent
`in
`communication
`between
`countries
`where
`access
`costs
`require
`a
`seridus PurP°se
`and mitigate
`against
`casual
`browsing.
`Fortunately
`numbers
`transcend most
`language barriers.
`The few f°rei9h W°rds
`aPPearin9
`On
`such
`pages are easily learned since this kind of
`data
`is usually presented in a fixed form.
`In fact computer subroutines to
`substitute
`the vernacular
`in
`fixed form pages are
`trivial since these words don't change.
`
`SIGNAL FORMAT
`
`compatibility is
`of
`The third level
`signal
`format
`easily
`discussed.
`also
`involves transmission schemes
`and
`coding
`schemes.
`Translation between different
`standards
`is
`done
`with
`relatiVelY
`ineXPensiVe
`anal°9 and digital electronic
`equiPment-
`If a Eur°Pean data base
`is
`t°
`be imported for sale and/or distribution in
`the United States:
`the
`imP°rter
`has
`3
`relatiVelY min°r eapital
`investment
`in
`the
`signal
`format Changing equiPment-
`N0 humah
`intervention is
`required- This equiPment
`Cost is
`dwarfed
`bY
`the Other
`equiPmeht
`costs. Consumer access to differing signal
`formats
`is more
`limited-
`Certaih1Y:
`a
`world wide
`signaling format
`would
`be
`
`an
`not
`is
`this
`of
`lack
`But
`utopian.
`information
`to
`impediment
`overwhelming
`An
`interesting example
`of
`interchange.
`third
`level
`compatibility
`overcoming
`problems is the use of viewdata by teletext
`information
`providers
`to modify
`pages.
`Teletext and viewdata
`signal
`formats
`are
`very different
`indeed. Yet communication
`between these two systems is economical and
`active in the U.K. Teletext IP's can
`have
`direct
`control
`of
`their
`pages‘ contents
`from their viewdata alphanumeric terminals.
`
`PAGE FORMAT
`
`compatibility
`This leaves second level
`involves
`the
`discuss.
`Page
`format
`to
`number of characters per row and the number
`of
`rows per
`page.
`If
`these
`are
`not
`identical
`between
`systems,
`human
`intervention will probably
`be
`needed
`for
`neat
`reformating. This is especially true
`for graphics.
`It is important
`to note that
`the Europeans have all
`agreed on
`twenty
`four
`rows of forty characters. ASCII—like
`code
`and
`mosaic
`graphic
`are
`used.
`Unfortunately, North Americans are divided
`on the
`issue
`of
`page
`format.
`If
`this
`division is not resolved,
`the advantages of
`electronic signal format conversion and the
`international usefulness of statistical and
`scheduling data will be impaired.
`
`32 vs. 40 CHARACTERS
`
`the horizontal
`two dimensions,
`the
`Of
`is
`especially
`is the most critical
`and
`difficult for graphics. Fortunately only a
`few
`proposals
`involve
`less
`than
`forty
`characters per row.
`Most proposals
`have
`followed the European lead,
`In principle, word processing can be
`used to reformat lines to other than forty
`characters
`by
`splitting lines
`between
`is
`words.
`This
`clumsy, wasteful
`and
`expensive,
`but doable.
`The same cannot be
`done for graphics.
`There
`have
`been
`two
`motivations
`put
`forth for
`going to less
`than forty characters. First has been
`the
`concern
`for
`bandwidth
`limitations
`in
`set—top adapters and the
`second
`has
`been
`the desire
`to make a minimal modification
`in British teletext
`for United
`States
`application.
`The U.S. bandwidth for NTSC
`can support color
`television displays
`of
`forty
`characters
`per
`row.
`Care
`and
`intelligent design are required. Perfectly
`useable
`results
`are
`relatively
`easily
`attainable
`and quite good results are well
`within reaCh_ Figures 11 and
`16 will
`be
`discussed
`further
`below, but
`they provide
`the evidence that forty characters per
`row
`is practical
`for
`set—top
`adapters.
`The
`second motivation for
`less
`than
`forty
`characters
`per
`row is
`to
`accomodate
`a
`minimal change in British teletext.
`The
`British system has
`been described
`as a
`synchronous system in that one complete row
`of
`characters
`is
`transmitted
`when
`a
`horizontal
`iine of data
`is
`sent,
`The
`timing of the transmission is locked to the
`television signal
`timing.
`For
`forty
`
`PMC Exhibit 2063
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`PMC Exhibit 2063
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`Ciciora, Sgrignoli, Thomas: Introduction to Teletext and Vicwdata
`
`243
`
`signal
`a
`generates
`this
`characters,
`bandwidth which exceeds U.S. standards.
`A
`simple solution is to send fewer characters
`per
`row.
`Much
`of
`the same logic can be
`made to directly apply. while
`this
`is
`a
`possible
`solution,
`the
`incompatibility
`penalty is,
`in
`our opinion,
`too high
`a
`price to pay.
`Since other modifications of
`the British system have been proposed, this
`approach is not
`the only alternative.
`
`20 vs. 24 Rows
`’
`concern in the vertical
`of
`cause
`The
`direction is over the U.S. 525 line
`raster
`versus
`the European
`625 line raster.
`It
`will be demonstrated that there
`are quite
`reasonable
`solutions. But first the point
`should
`be made
`that
`this
`is more
`an
`applications
`problem
`than
`a
`standards
`problem.
`The nature of the
`binary
`number
`systems
`causes the British teletext system
`to have thirty two rows. This
`is
`because
`four bits
`of
`row number data allow for
`sixteen rows which is not enough
`and
`five
`bits
`of
`row number data makes thirty two
`rows possible.
`If one wished
`to make
`a
`Private
`sYstem based
`0“ high Fes°1Uti0n
`monitors,
`thirty two
`row
`teletext
`or
`viewdata
`would
`be possible without
`a
`standards
`change,
`just
`equipment
`and
`application's
`policy
`changes would
`be
`needed. Likewise choices between twenty to
`tWentY f°UF YOWS are P°1iCY and
`equipment
`questions,
`not
`true
`standards questions.
`Admitted1Y: a semantiesist maY argue
`about
`the meaning
`of
`the word "standard", but
`this should not be allowed to obscure
`the
`point.
`there
`(NTSC television).
`the U-S-
`In
`are 525 lines per frame.
`of these, 485 are
`active.
`the remainder being given over
`to
`the
`vertical
`retrace
`interval.
`To
`accomodate tolerances
`in
`receiver design
`and
`aging
`of
`circuits,
`receiver
`manufactureres design in
`raster overscan.
`The
`Society
`of Motion
`Picture
`and
`Television gngineers TSMPTE) defines a Safe
`action area of 436 lines.
`SMPTE safe title
`area is 388 lines. This
`is
`conservative.
`This yields
`194
`lines per field for safe
`display of teletext
`or
`viewdata.
`Twenty
`four
`rows in 194 lines yields 8 lines/row.
`A S x 7 matrix in a
`6
`x
`8
`box produces
`acceptable
`results
`on
`both
`built—in and
`antenna terminal decoders.
`See figures
`10
`and 11.
`
`RASTER MANIPULATION
`
`Unfortunately a 7 x 9 matrix in an 8 x
`10 box won't fit on the screen even
`though
`it will
`fit
`in
`the
`active
`lines.
`See
`Figure 12. However,
`the built-in decoder
`has
`an
`advantage
`here.
`Because
`the
`receiver is designed to accomodate teletext
`and viewdata, raster overscan can
`be more
`carefully controlled.
`Furthermore, when in
`teletext
`or
`viewdata
`mode,
`raster
`compression can be introduced to allow all
`active
`lines
`to
`be
`visible on
`the
`television screen.
`This
`is
`actually
`
`in the vertical direction.
`required only
`See Figures
`13,14,
`and
`15.
`This
`is
`a
`relatively simple circuit modification.
`the
`Yet
`another
`alternative
`for
`number
`built—in decoder is to increase the
`of
`scan
`lines
`for
`the text and graphics
`mode. This is not as wild an
`idea
`as
`it
`may
`at
`first
`appear.
`Modern
`se1f"C°nVeF9in9 in'1ine CRT sYstems can
`be
`made
`to accomodate this with little or no
`change.
`The horizontal scan
`frequency
`is
`essentially unchanged.
`The vertical scan
`rate is changed to allow for more
`lines.
`Moire will in general be reduced with this
`technique.
`raster
`that
`object
`may
`Some
`impair the appearance of
`manipulation will
`"mixed mode".
`Mixed
`the picture in
`the
`mode
`is
`the
`simultaneous display of the
`televised picture
`and
`the
`text
`and
`9faPhi°5- While
`this is true: it must be
`emphasized that mixed mode is not
`expected
`to
`be
`the
`usual method
`of use since it
`makes
`both
`reading
`text
`and
`viewing
`television difficult. Raster manipulation
`has no impact on
`captioning or
`newsflash
`modes
`since
`in
`these
`cases
`the text
`is
`displayed near but not at the bottom of
`the
`picture.
`
`SET_T0p ADAPTER FORMAT
`
`adapter
`set—top
`Returning back to the
`an
`even better
`case,
`Figure
`16
`shows
`approach to text display. Note the 24
`row
`40
`character format.
`The characters are 5
`x 7
`in a
`6
`x
`8
`box.
`But‘
`rather
`than
`display white
`or
`colored characters on a
`black
`background,
`much
`more
`pleasing
`results
`are
`obtained with only
`black
`characters
`on white
`or pastel
`colored
`backgrounds.
`The
`full
`impact
`of
`this
`special
`treatment
`cannot
`be
`appreciated
`from a still picture.
`Figure
`11 looks
`better
`than
`real
`life
`because
`the
`photograph
`has
`integrated out
`the color
`subcarrier
`dot
`crawl.
`The
`approach
`of
`Figure 16 minimizes the deliterious effects
`of
`dot
`craw1_
`The main purpose of Figure
`16
`is
`to
`illustrate
`that
`there
`are
`significant
`alternatives
`to be considered
`when studying methods
`of presenting text
`and graphics on color televison receivers.
`Mixed mode operation will
`likely not be
`available on most
`set—top
`adapters
`since
`this
`significantly increases
`the cost of
`the adapter. This is because the circuits
`will
`have
`to demodulate,
`process,
`and
`remodulate sound. Also the text will
`have
`to be inlaid into the video.
`
`SYNTHETIC VIDEO
`
`clearly held in mind that
`be
`It must
`the image displayed on the CRT is synthetic
`video
`and
`that
`the
`synthesis
`is
`done
`1oca11y,
`The designer
`of
`the receiving
`equipment has many options at his disposal.
`The designer can be relied upon to come
`up
`with many
`clever
`and
`innovative ways to
`synthesize
`video
`for
`the
`particular
`application,
`set—top
`adapter or built-in.
`
`PMC Exhibit 2063
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`

`
`244
`
`IEEE Transactions on Consumer Electronics, Vol. CE-25, No. 3, July 1979
`
`not
`should
`standards‘ writers
`The
`the
`underestimate
`the
`ingenuity
`of
`equipment designer.
`They need not encumber
`world—wide video text display systems with
`a different page format standard.
`
`A FINAL ARGUMENT FOR 24 ROWS
`
`be two applications
`to
`appears
`There
`for non—graphic characters to be displayed
`on
`a
`CRT
`screen.
`In
`one
`application,
`tables
`of
`numbers
`or
`schedules
`are
`displayed,
`in
`the other application,
`text
`is presented.
`In the former application, a
`high density of information
`is desireab