PMC Exhibit 2069
`PMC Exhibit 2069
`Apple v. PMC
`Apple v. PMC
`|PR2016—OO753
`IPR2016-00753
`Page 1
`Page 1
`
`

`
`‘Electronics, Television, Radio. Audio ~
`
`MAY 1977
`
`Vol 83
`
`.No‘1497
`
`Contents
`
`,
`
`35 Surround sound — time to consolidate
`36 Radio in the ’80s by Duncan MacEwan
`41 BBC Matrix H by P. A, Ratliffe and D. J. Meares
`46 World of amateur radio
`_
`47 Automatic electrolytic tester by A. Dmmmond-Murray
`50 Varioniatrix adapter for System 453 and Matrix H
`by Michael A Gerzon
`51 H.F. predictions
`52 Logic design -— 4 by B. Holdsworth and D. Zissos
`, 55 Viewdata — 4 by S. Fedida
`'
`60 Letters to the editor
`'
`
`Mobile radio planning
`Do-it-yourself biofeedback
`Audibility of phase effects
`News of the month
`
`Annan andtechnology
`‘
`ITU Conference results
`British Rail high-speed track measurements
`Two-stage linear amplifier by Helge Gronberg
`Power semiconductors — 2 by Mihe Sagin
`Circuit ideas
`
`Linear Voltage/frequency converter
`Pulse-counting frequency comparator
`Op-amp power output stage
`I
`New tomography machine by John Dwyer
`New products
`‘
`‘
`APPOINTMENTSVACANT
`INDEX TO ADVERTISERS
`
`‘ Pdéwilvlulupe
`rqmmnlr
`'
`Ketlvnliiue
`
`Front cover is a print produced
`by the Tomoscanner, described _.
`by John Dwyer on page 82 of‘ ~
`this issue. Print supplied by J. & .
`P. Engineering (Reading) Ltd.
`
`IN OUR NEXT is‘s’Ui=;"
`Loudspeakers and rooms.‘ A
`. discussion by James Moir of the
`-interaction between the output of
`a loudspeaker and the acoustic
`‘performance
`of
`the
`listening
`room_.
`
`vMatrix H decoding. Circuit
`details of a matrix H variable
`matrix decoder, a development of
`Sansui's Variomatrix, for use with
`experimental
`surround-sound
`programmes.
`'
`
`Using a microprocessor. The‘
`start of a series oi articles on the
`design of a typical processor—bas—
`ed control system, starting with
`no assumptions of prior knowled-
`ge on the reader's part.
`
`Current issue price'40p. back issues (if available) 501:». at. Retail and Trade Couiitler, Paris Garden.
`London SE1. By past. current issue 55p. back issues (if available) 50;). order and payment to Room 11.
`__Doi'set House. London SE1 QLU. -,
`'
`~
`Editorial ‘Er. Adi.'erlisi_fi'offices: Dorset House. Stamford Street. London SEl 9LU'.'
`.Telcplioiies:>Editorial 0|-‘ZGI 8620: Advertising 0|-26! 8339. .
`Telegrams(Telex, Wlworld Bisnespres 25137 BISPRS G. Cables. "Ethaworldt. London SE1..
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`0444 59188. Subscribers are-requested to notify a change of address.
`l.P.C. Business Press Ltd, 1977
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`NY 10022. 2nd-class postage paid at New York.
`
`ls‘s‘N oo43 6062
`
`lnllllullnllll emu;
`vim Aywmits
`
`PMC Exhibit 2069
`Apple v. PMC
`IPR2016-00753
`Page 2
`
`

`
`Wireless World, May 1977
`
`V‘
`
`d ata
`
`4' §— The Viewdata terminal in more detail
`
`by s. Fedida, B.Sc.(Eng.), M.Sc.,.F.|.E.E.V, A.C.G.l,
`
`Post Office Research Centre
`
`A Viewdata decoder may be considered
`as being made up of six parts, as shown
`from left to right in Fig 1(a): a line
`isolation unit; a modem; a keypad; an
`input processor; a store (possibly
`r.a.m.); and an output processor. Indeed
`the breakdown of facilities is very simi-
`lar to that of teletext, shown in Fig. 1(b).
`This diagram also indicates that, apart
`from additional minor interconnections,
`parts common to Viewdata and teletext
`are the store and output processor.
`These are substantial components and
`therefore combined Viewdata/teletext
`receivers show important savings over
`two separate decoders for the two ser-
`vices. This is a slightly over-simplified
`picture but the situation will be clarified
`later.
`‘
`' Note however, an important differ-
`ence.'The input circuits in Viewdata,
`up to and including the store are bi-
`directional, thus highlighting the inter-
`active nature-of the system. On teletext
`the input circuits are one way only.
`
`Line transmission
`The transmission code used over the
`telephone line between the Viewdata
`terminal and the computer is at present
`8-bit, 10-unit asynchronous (or start
`stop)» as shown in Fig.2. Each character
`
`10 unit code
`8 bit character
`10110011 = character M
`
`Parity bit (odd parity)
`
`Fig. 2. Transmission code used between
`a Viewdata terminal and the computer
`is an 8-bit, 10-unit asymthrunnus code.
`
`_consists of an 8-bit code, the first 7 bits
`containing the information while the
`8th bit is a parity bit. Preceding each
`character is a start bit, with a stop bit
`terminating the character. The cha-
`racter illustrated in Fig. 2 is M, with odd
`parity. A lovunit asynchronous system
`
`Fig. 1. Comparing the main sections of
`(a) a Viewdata decoder with (b) those of
`a taletext decoder
`
`was chosen tor simplicity. It is clearly.
`not as efficient as a synchronous trans-
`mission mode, in which characters fol-
`low each other without the intervention
`of start and stop bits, but it is simpler to
`implement and is currently used by
`many time-sharing computer systems.
`In order to transmit this code over a
`telephone line, a modem (modulator-
`demodulator) is required. Essentially
`this device modulates the code on to a
`Voice frequency carrier, -within the
`speech band, thus obviating the pro-
`blems encountered with Very low fre~
`quency transmission over the telephone
`network. The modem also enables the
`go and return transmission to take place
`
`Input
`processor
`
`To tv
`display circuits
`
`Input
`processor
`
`5:
`
`Output
`processor
`
`TO tv
`‘
`display circuits’
`
`PMC Exhibit 2069
`Apple v. PMC
`IPR2016-00753
`Page 3
`
`

`
`Wireless World, May 1977
`
`Teletext
`
`cl ate
`
`7 ‘
`
`I
`
`selector
`
`Teletext address
`
`Vlewdata
`r=i='=-='=l‘r*l
`=5“ 2 =n =
`ll.
`
`I]
`
`5‘ ll:
`H
`--------------—3---
`ll
`
`fl
`
`[i
`
`read address
`
`it
`
`‘ Random
`2 CCSSS
`ory
`
`"simultaneously over the two-wire tele- -
`phone line.
`Transmission rates selected for
`Viewdata during the present experi-
`mental phase are 1200 bits per second
`from computer to terminal and 75 bits
`per second in the reverse direction.
`in the computer-to-terminal direction
`as high a transmission rate as possible is
`desirable in order to achieve a fast
`picture build-up. 1200 bits per second
`was chosen to fit in with a well tried and
`readily available modem. For the majo-
`rity of Viewdata displays, consisting for
`example of mainly alphanumeric (Sha-
`lracters, the picture build-up is much
`faster than can be read by the user, and
`hence quite adequate from this point of
`view. Where,_. however, large uniform
`areas of graphics are displayed, the
`build-up. may appear rather slow (the
`display shows repetitive information),
`and improvements to the build-up in
`this case may be obtained by using
`special means. But in general the
`additional complexity is not really
`Worthwhile.
`V
`.
`In'the direction from terminal to
`computer the bit rate of 75 bits per
`second (7.5 characters per second) is
`quite adequate for hand keying.
`The frequencies used in line trans-
`mission are as follows:
`Forward channel:
`(from terminal
`to computer)
`
`binary l = 390 Hz:
`binary 0 =450 Hz
`
`Return channel:
`(from computer
`to terminal)
`
`binary l= l30O HZ
`
`binary 0 ==2l00 H2
`
`When no data transmission is taking
`- place on the line the terminal is trans-
`mitting continuously at 390Hz and the
`computer at 13001-lz. These tones are
`used in the modems at either end of the
`line to.provide an indication of conti-
`nuitygwhich as we shall see below is of
`‘ some importance in the operation of the
`whole system.
`‘
`When data is beingtransmitted the
`
`Fig. 3. Simplified block diagram of a
`Viewclata terminal, with adaptation to
`teletext shown in broken lines. The
`number and bar on certain connecting
`lines indicate that the line is carrying
`parallel information onthat number of
`‘wires.
`-
`
`carrier is frequency modulated (fre-'
`quency shift keying), between the
`binary 1 and binary 0 frequencies, the_
`‘change being smoothed out to give a‘
`gradual transition between the fre-
`quencies.
`The transmission arrangement used
`at present is duplex, with “echoing”
`facilities provided from the computer to
`the terminal. In a duplex system trans-
`mission may take place in both direc-
`tions at once over the telephone with no
`mutual interference (hence, of course,
`the choice of frequencies). Characters
`keyed at the terminal are‘ first trans-.. '
`‘mitted by the modem to the computer
`and displayed only when they are
`“echoe ” back. This arrangement gives
`some important advantages. First, it
`provides a measure of error detection,
`the user being aware of any corruption
`in transmission, errors in the computer
`or mis-keying errors, Secondly, duplex
`working also increases the user's confi-
`dence in the working of the system, as
`“echoed” characters provide a continu-
`ous indication that the whole system is
`in satisfactory order.
`-
`“Echoing” from the terminal to the
`computer is not necessary. A parity
`check is sufficient to provide for the
`detection of the majority oferrors, the
`computer usually responding in these
`cases by requesting a repetition of the
`instruction; The computer also moni-
`tors continuously the terminal carrier,
`thus ensuring that a‘ line break is noted
`as soon as it occurs. This avoids the
`possibility of the user being incorrectly
`charged for using the system after the
`occurrence of a line interruption.
`
`Experimental Viewdata terminal
`The experimental Viewdata terminal at
`present in use is best introduced in two‘
`parts; (a) the data transmission unit,
`which deals with the Viewdata. signal
`between the telephone line and the
`internal store, and (2) the display unit,
`which deals with the Viewdata signal
`between the store and display device.
`(the c.r.t. of a television set). As
`explained earlier, much of the display
`part isvcommon with teletext.
`A typical arrangement of a Vicwdata
`‘terminal is shown in Fig. 3. There are
`four major units as follows: the data
`‘ transmission unit (1); the address selec-
`tor (2); the random access memory (3);
`and the display unit (4).
`The address selector (2) is the only
`unit which interconnects the input and
`output processors, essentially for the
`-purpose of preventing mutual interfer-
`ence..Unlike the situation in teletext ‘
`data is received at random times from
`the . telephone
`line,
`completely
`unsynchronized with the operation of
`the display. It is therefore necessary to
`organise the access to thememory for
`reading out and display on the one
`hand, and writing-in incoming charact-
`ers on the other hand. without cross-
`interference. This function is carried
`out by the address selector. The’ writc
`address generated in the data transmis-
`sion unit (1) and the read address gene-
`rated in the display unit (4) are both
`available at the address selector.
`A mixed blanking waveform, also I
`generated in the display unit, indicates
`the times at which characters are
`required to be extracted from the
`memory for display purposes essentially
`during 40 microseconds ofgevery line‘
`period. excluding blank lines at the t0?
`and bottom margins of the display-
`During these times incoming characters
`are made to dwell a little longer in an
`input character buffer in the data
`transmission unit and the address sup’
`plied to the memory is the read address-
`. At other times the write address 15"
`
`Page 56
`
`PMC Exhibit 2069
`Apple v. PMC
`IPR2016-00753
`Page 4
`
`

`
`57.
`two pairs of opposite polarity gas
`-dischargevtubes, each pair connecting
`one of the telephone wires to earth. It
`‘ensures that voltages originating from
`the terminal arelimited to safe values
`before entering the telephonenetwork,
`It also contains fuses, in series with each
`telephone wire and on either side of the
`gas discharge tubes, to limit the current
`flowing. The gas discharge tubes have a
`striking voltage of about 150V. to avoid
`breakdown in the presence of ringing
`tones originating in the telephone line.
`Following the isolator is the modem
`., control unit, which contains a relay
`operated by the “data” button on the
`telephone: When this button is
`depressed it switches the telephone line
`from the telephone receiver to a hybrid
`transformer within the control unit.
`This separates the go and return chan-
`nels connected to the modulator and \
`- demodulator respectively.
`The incoming Viewdata signal is
`superimposed on an f.sJk. (frequency
`‘shift keying) carrier, binary 1 corre-
`sponding to a frequency of l300Hz and
`binary 0 to a frequency of z100Hz. The
`incoming‘carrier first goes through two
`stages of bandpass filtering to eliminate
`unwanted signals. After this it is fre-
`quency shifted by lOkHz, thus becom-
`ing a frequency modulated carrier
`centred on ll.7kH.z with a deviation of
`:4DOHz, the modulation rate being
`1200 per second. Frequency shifting the
`carrier by 10kHz makes the demodula-
`tion process much easier by virtue of
`increasing the number of carrier cycles
`per modulation cycle.
`The incoming carrier is now applied to
`‘an unbalanced discriminator anda
`detector which extracts the data modu-
`lation. After filtering, amplification,
`squaring and level changing the data
`
`l o
`
`ffers assembled characters to the con-
`trol codes decoder (9). It also triggers '
`the operation of the timing unit (10)
`which generates the necessary wave-
`forms used throughout the data trans-
`mission unit. The control codes decoder
`recognises the special control charact-
`ers used in Viewdata, initiates the cor-
`responding control functions and
`enables the memory (8) to store the
`"appropriate characters. It also controls
`thememory address unit (11), which
`maintains arecord of the addresses at
`which incoming characters are to be
`stored and instructs the terminal iden-
`tifier (12), to generate the automatic.
`identification code in reply to an
`enquiry signal receivedfrom the View-
`data computer.
`The transmission control unit, the
`timing unit and the page transmission
`unit (7) together control the transmis-
`sion of a complete page from the termi-= '
`nal to the computer. The keypad unit
`(13) generates and encodes the terminal
`responses and outputs these direct to
`the modem. for transmission to the
`computer.
`The data transmission unit operates
`in two different modes: reception mode
`and transmission mode.
`
`‘
`
`Reception of Viewdata signals
`isolator and modem. The Viewdata
`signal enters the terminal from the
`telephone line, after passing through
`the isolator. This may consist simply of
`
`Fig. 4. Data transmission unit at
`Viewdata terminal. The number and
`bar on certain connecting lines
`indicate that the line is carrying
`parallel information on that number
`of wires.
`
`Wireless World, May 1977
`
`switched to the memory. The address
`selector also notes the coincidence be-
`tween the read address and the write
`address when it delivers a pulse to the
`display unit to initiate the generation of
`the cursor display (see Part 3).
`Shown also in Fig. 3 in broken lines,
`are the units required for interfacing
`Viewdata with teletext. In a receiver
`already fitted with a teletext decoder,
`one additional unit is required: the data
`selector (5), while the Viewdata display .
`unit may be dispensedwith and the
`teletext display unit (6) used instead.
`The connections required are shown
`also as broken lines. A-Viewdata/tele-
`text switch unit (7) is also shown. This
`sets data and address selectors to
`Viewdata» or teletext as required.
`'
`In the teletext mode the address and
`data selectors switch the memory to the
`teletext input circuits, while in the
`'1/iewdata mode the memory is available
`to Viewdata. The read address,
`however, is now provided by the tele-
`text address. which scans the memory
`during the mixed blanking period.
`
`Data transmission unit
`The data-transmission unit is shown in
`more detail in Fig. 4. This consists of a
`line isolator (1) and a modem (2, 3, 4),
`the last-mentioned including a modula-
`tor (4) which transforms-the outgoing
`data stream to a voice frequency signal,
`a demodulator (3) which accepts a voice
`frequency signal from line and extracts
`the data stream from it, and a control
`circuit (2) which switches the connec-
`tion of the telephone line to the tele-
`phone receiver or to the modem.-
`The transmission control unit (6),
`which is synchronized by the clock unit
`(5), accepts the demodulated data in
`. serial form, checks character parity and
`\
`u
`
`inhibit count
`1MHz clock
`Reset character
`Reset row
`
`Up/down
`Disable character
`
`Device
`control
`latches
`
`Demoduiator
`Control
`unit H )
`(2)
`(3
`
`Carrier
`fail
`
`Modulator
`(4)
`
`,
`
`V
`
`.
`Transmission
`control
`,
`
`Control codes
`decoder
`
`Keyboard
`. encoder &
`
`Keypad (T3) '
`L _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ___j
`
`Page ‘
`transmission
`unit
`(7)
`
`.
`-
`'-
`-
`Tmmg mm‘
`(70)
`
`‘
`
`Terminal
`identifier
`(12)
`
`PMC Exhibit 2069
`Apple v. PMC
`IPR2016-00753
`Page 5
`
`

`
`.58
`
`signal is fed out to the transmission
`control unit at a level of —6V for a
`frequency of 13001-lz (binary l) and
`,+ (iv for a frequency of 2l00Hz (binary
`O).
`The transmission control unit. The
`transmission control unit accepts data
`in serial form and, using a sampling
`technique controlled by the clock gene-
`rator, recognises‘ the start and stop bits
`of each 10-bit character sequence, and
`stores each character in a temporary
`buffer. This-completed, it signals the
`event to the timing unit, and control
`codes decoder, i.e. that a character has.
`been received and is available for
`transfer at the input data highway in a
`'7-bit parallel form. '
`The transmission control unit also
`checks character parity and feeds out
`IPE (input parity error) to the control
`codes decoder ‘if parity is found in error.
`
`The timing unit provides a number of
`Waveforms which control the storage of
`characters in the memory. On receipt of
`a “data available” signal from the
`transmission control unit, it transfers
`the intended location of the received
`character from memory address to
`memory, enables memory to accept the
`character, clocks memory address to
`the next character position and resets
`the transmission control unit to indicate
`that the character received has been
`accepted.
`
`The control codes decoder accepts
`incoming characters from the input
`, data highway, decodes the special con-
`trol codes and initiates the appropriate
`actions as follows. The unit is “trans-
`parent" to all characters other than
`control codes, the former being ap-
`plied direct to the memory to be stored
`therein.
`The control codes decoder performs
`the following functions. On receipt ufz‘
`(a) Non storing characters such as NUL,
`CR, LF, BS, FF, etc. it inhibits their
`storage in memory. (Write disable to
`timing unit.)
`(b) BS, it causes memory address to V
`count down one character
`(c) VT, it causes memory address to
`count down one row.
`(d) CR, it causes memory address to be
`reset to character address of zero, leav-
`ing row address unchanged.
`(e) LF it causes memory address to
`count up one ro\v.
`(f) FF it causes memory address to be
`reset to character address of zero and
`row address of zero. It also causes the
`complete content of memory to be
`erased by setting the code on the input
`data highway to “space” and entering:
`this in the whole memory.
`(g) ESC it causes bit 7 of the received
`character to be changed from 1 to 0.
`before storage.
`(h) DC} to DC4, it sets latches to control
`internal devices.
`The control codes decoder, when
`receiving input parity error, substitutes
`
`character 7/15 for the character re-~
`ceived in error before itiis entered in the
`memory. The implementation of
`memory and memory address may be
`either in the form of a random access
`' memory or a series of shift registers. A
`r.a.m. appears to lend itself to a rather
`simpler logic circuit than a shift register
`memory and because of this has been
`assumed in the description of the ter-~
`minal.
`The memory address consists of
`characters and row counters which are
`controlled by the control codes decoder
`to indicate the address at which the
`next character is to be stored in the
`memory.
`
`.
`
`Transmission of Viewdata signals
`The transmission of Viewdata signals
`originates either from the keypad unit
`or the page transmission unit.
`The keypad unit controls a keyboard:
`connected in a cross-matrix of 5
`columns and 9 rows, with a shift button,
`which together with the 45 keys, pro-
`vide a maximum of 90 codes. The basic
`keypad with which most of the View-
`data facilities may be used provides only,
`12 codes, (0 to 9),
`* and #, with
`additional optional codes for automatic
`calling.
`In both cases the output of the key-
`board matrix is applied to an encoder
`which generates codes appropriate to
`the keys selected, serializes the bit pat-
`tern thus obtained, adds parity. start
`and stop. bits and applies the resulting
`data stream directly to the modulator,
`under the control of an internal timing
`unit which generates the appropriate
`clock signals. Characters fed out are not
`displayed on the screen until they have
`been “echoed” backyby the computer.
`The page transmission unit operates
`jointly with the transmission control
`unit and timing unit, and its operation is-
`initiated manually by a push-button on
`the terminal. This causes the page
`transmission unit to reset memory,
`address zero and enables transmission
`buffer empty (TBE) signal from the
`transmission control unit to start the.
`timing unit (using the page transmis-
`sion enables signal). It also inhibits the
`writing into memory, via write disable
`to timing unit.
`_
`On receipt of TBE, the timing unit
`generates a load signal to the transmis-
`‘ sion control unit which causes the latter
`"to accept a character from memory, and
`to clock it out in serial form at 75 bits.’
`second, complete with start, stop and
`parity bits, to the modulator. The timing
`unit also increases the memory address»
`count by one. When a character has
`been discharged from the transmission
`control unit, the next transmission
`buffer empty signal recommences the
`above cycle on the next character.
`When 960 characters have been'se_nt
`out, the page transmission unit notes
`the fact and resetsithe terminal to the
`quiscent state.
`At the beginning of a Viewdata ses-
`sion the computer interrogates the
`
`Wireless World, May l977
`built-in terminal identifier. The control
`codes decoder initiates the operation of
`this unit, which sends out an identifica-
`tion code to the transmission control
`unit. This code is transmitted to the
`modulator, complete with start, stop
`and parity bits. The operation is similar
`to that of the page transmission unit
`except that the identification code is
`stored in the terminal identifier.
`
`Display unit _
`is shown in more‘
`The display unit
`detail in Fig 5. The function of the
`display unit is to generate line and
`framesynchronising signal for the tele-
`vision raster, to decode the special
`display control characters for colour
`and graphics and to generate alphanu-
`meric and graphic symbols for display.
`As mentioned earlier, the display unit
`is nearly identical to the corresponding
`part in the teletext decoder. The major
`differences are in the line and frame
`synchronising generators and in the
`provision for the cursor, which is not
`required in teletext. With respect to the
`line and frame synchronising pulses,
`these are essential in a Viewdata-only
`receiver since it
`is required that the
`Viewdata service should be available at
`all times and not just during tv broad-
`casting hours; thus it is not always
`possible to rely on the presence of tv line
`and frame sync to maintain the raster.
`The provision of line and frame sync
`pulses is also very useful in a combined
`Viewdata/teletext decoder, as indeed in
`a teletext-only decoder, since it is pro-
`vided in teletext that viewers should be
`able to store a page of information
`transmitted during tv broadcasting
`hours and to View it later at their con-
`venience. possible outside broadcasting
`hours.
`The display unit consists of a sync
`generator and memory scanner (1), a
`display control codes decoder (2), an
`alphanumeric character generator (3), a
`graphics generator (4), a character
`rounding unit (5), and an output unit
`(6).
`The sync generator and memory
`scanner generates line and frame
`synchronising pulses which are applied
`to the tv timebase generators, and row
`and character addresses which are
`applied to the r.a.m. via the address
`selector. The unit derives these wave-
`, forms from an 8MHz crystal controlled
`master oscillator followed by a chain of
`dividers. The extraction of characters
`from the memory and their display on
`the screen occurs at a rate of lMHz.
`which is derived directly from the 8MHz
`clock by a divide-by-8 circuit, a further
`division by 64 providing the line
`synchronizing pulses. There is a certain
`amount of flexibility in the choice of
`master oscillator frequency; a lower
`frequency, say 7lVlHz or 6MHz, giving a
`wider character on the display, while.
`not being quite so demanding on the
`width of the video passband. The width ,
`of individual characters may also 59
`altered by adjusting the blank marginfi
`
`~
`
`C
`
`PMC Exhibit 2069
`Apple v. PMC
`IPR2016-00753
`Page 6
`
`

`
`Wireless World, May 1977
`
`Data out
`
`Random
`BCCGSS
`memory
`
`Display
`control codes
`decoder
`(2')
`
`Line
`address
`
`Alpha
`generator.
`(3) '
`
`U1 put 1
`0
`*———.j—
`Output 2
`.>.:_
`
`Character
`rounding
`(5)
`
`Odd / even
`
`frame sync
`_
`to
`tlmebase
`generator
`
`Sync generator
`and
`memory
`scanner
`(1 )
`
`8MHz
`
`clock
`
`Odd /even
`
`Graphics
`generator
`(4)
`
`to the ‘left and right of the page on
`display. The choice of 8MHz here is
`mainly of convenience to simplify the
`subsequent dividing circuits. The sync
`generator and memory scanned must
`also generate the mixed blanking
`waveform which provides the margins
`around. the display area. Thus every l MS
`a read signal is applied to the ram.
`which then feeds out the Character
`stored at the location indicated by the
`row and character addresses generated
`. by the unit.
`-
`The timing of the whole display unit
`must take into account delays occurr-
`ing in the r.a.m. and in the alpha-
`numeric character generators. These
`delays may be each of the order of 200 to
`600 nanoseconds, depending on cost,
`the faster unit obviously being more
`expensive. Thus in order to take up
`these tolerances» and allow the cheaper
`units to be used, a Zps delay is allowed
`for from the instant a character is
`requested from memory to the time it is
`displayed.
`‘
`As in teletext, a row of characters
`consists of 10 television lines in each
`frame (20 lines counting the interlace),
`made up of 7 display lines and 3 spacing
`lines, each character space in_ the
`horizontal direction consisting of 8 dots,-
`5 display dots and 3 space dots, the dots
`occurring at the SMHZ rate.
`As each character is fed out from the
`memory it is transferred to the display
`control codes decoder which is pro-
`grammed to recognise the characters in
`columns 0 and l of Fig 7 in the April
`issue, i.e. the special colour, graphics
`and other display control characters;
`provide blanking for the duration of
`these characters (since these are non-
`display characters); and inhibit
`the
`character generator or graphics gener-
`ators as appropriate.
`At the beginning of every row of
`characters all the latches are set to
`white, alphanumeric, steady according
`to the teletext convention. The output
`
`Fig. 5. Display unit at Viewdata
`terminal. The number and bar on
`Certain connecting lines indicate that
`the line is carrying parallel information
`on that number of wires. Some
`commercial Viewdata tv receivers may
`have clock frequencies other than 8
`MHz.
`
`of the decoder is applied the output unit
`. which provides R, G, B signals to the
`guns of the cathode-ray tube.
`Non-control codes are applied to the
`alphanumeric character generator
`which generates the required character
`‘ pattern. This generator also receives a
`.4-bit line address from the sync genera-
`tor, which indicates which line out of
`the ten lines required for character
`display has been selected at any one
`time. When a line of dots is fed out from
`the character generator it is entered in’
`5-bit parallel formin a 5-stage shift
`register and clocked out in the next l[l.S
`period at the 8MHz rate, under the
`control of the 8MHz clock.
`If a graphics control character is
`displayed, a latch is set in the display
`control codes decoder to indicate that
`all subsequent characters are graphics.
`i The inhibition is lifted, however, in the
`case of the “blast-through” characters ‘
`in columns 4 and 5 of Fig. 6 in the April
`issue.
`'
`Generation of graphic symbols is car-
`ried out under the control of vertical
`and horizontal bright-up waveforms,
`generated in the graphics generator.
`The horizonal bright-up waveform
`picks up left, right or both coloumns of
`the graphics symbol while the vertical
`bright-up waveform picks up one or
`more of the top, middle or bottom pair
`of squares in the graphics symbo1s.iThe
`7-bit graphic character is decoded with
`the aid of these two waveforms and
`control signals applied to the output
`unit.
`-
`
`The display of the Viewdata cursor is
`initiated by the address selector, which
`notes the coincidence of input and out-
`put memory addresses and enables an
`exclusive-OR gate in the output unit.
`This causes normal display of charact-
`ers when the cursor isoff, but inverted
`display (i.e. black on white) when the
`cursor is on. Thus characters on display
`may be read through the cursor.
`Character rounding is provided in the
`character rounding unit when this feat-
`ure is required, i.e. mostly with large
`screen displays. Character rounding is
`initiated by the odd/even signal gene-
`rated together with the line interlace
`pulse in the ‘sync generator unit. A
`second alphanumeric character genera-
`tor unit similar to unit (3) may be
`required, both units operating simulta-
`neously out of step by one line of the 7
`X 5 character matrix. The two outputs,
`one delayed with respect to the other,
`are compared in the character rounding
`unit and additional dot pulses generated
`half way in the 8MHz dot interval and
`transmitted to the output unit to give
`thé required result.
`The use of character rounding is not.
`necessary in the case of the small—size
`Viewdataphone display for ‘use in the
`office, and this results in a useful sim-
`plification.
`
`(To be continued)
`
`A limited number of commercial tele- ‘
`vision sets containing Viewdata/tele
`text decoders are now ‘being manufac-
`tured for marketing trials of Viewdata
`due to start in. March 1978. In a later
`issue we hope to publish an article
`outlining the main features of a typical
`commercial set of this kind.
`
`Page 59
`
`PMC Exhibit 2069
`Apple v. PMC
`IPR2016-00753
`Page 7