Note: Descriptions are shown in the official language in which they were submitted.
The present invention relates to television systems and
has as an object the provision of television systems for the
presentation of visual displays in a novel and convenient manner.
In any normal television system, -the transmission of
the wide band video signals which are to produce the actual
picture elements on the screen of the receiver, is interrupted
between the scanning period for line and field synchronisation
purposes. Consequently there are periods during which no video
signals are being transmitted. It is now possible to use these
periods for the transmission of data which is not necessarily
, . .
concerned with the video transmission itself.
Basically, data representable by standard graphical
symbols, such as alpha-nutneric symbols or low definition picture
components can be transmitted via a restricted channel provided
that the rate of transmissiorl is res-trlcted, It is now possible
to use periods aqi aforesaid, especially the line times of the
field blanking intervals (i.e. the times of the individual lines
occurring between fields which correspond with the times occupied
by video signals on active picture lines), hereinafter t'LTFB ,
for the transmission of pages of data. For example, using 8-bit
binary digital signals of the complemented type representing alpha- `~
numeric characters at a bit rate of 2.5 M bit per second, 50 pages
of data each consisting of 22 sitrips of 40 characters can be
transmitted repeatedly in a total cycle time of 90 seconds using
only a single line of the field blanking period per field of the
625 line system as operated in the United Kingdom. -
There is accordingly a requirement for a convenient form
,!", ,.
of apparatus for use in the reception of the pages of data.
In accordance with the present invention, there is
provided a television receiver system having a memory device -
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` _ 51342(B)
form of appara-tus for use in -the reception o~ the pages of
da-ta.
In accordance with -the present invention9 there is
pr~vided a television receiver system having a video circuit
for received video signals in the form of fields of picture
signals for display by an intensity modulated raster, ~aid
picture signals being separated in time by ~ield blanking
intervals each of which occupies several consecutive lins
pexiods, a coded-character signal memory device, selector means
responsive to a chosen start code for routing to the memory
device coded character signals received during the field
blanking intervals and accompanied by the chosen start ~ode
whilst i~noring other coded charactsr signal~ received during
said intervals, a reading device operable to read the coded
character signals from the memory device repeatedl~ and a
character generator resporlsive to the coded chara¢ter signals
read repeatedly from the memory device by the reading device
to provide an output of character signals for visual display ~ -
by the raster.
~or the purposes of the preserlt inventiorl, a page of
a series o~`-the kirld hereinbefore described is to be -
. .. . .
regarded as an information channel and the series o~ pages
is ko be regarded as a series of information channels~
~he selector equipment is preferably operable to
route the information to the storage device only duri~g
periods of time, corresponding with the single in~ormation
channel or s~all number thereof, separated by intervals
which are long compared with said periods, so that the
system is responsive to an information channel received
3 repeatedly at intervals. ~he said period~ may be o~ a
duratio~ corresponding with several fie-ds o~ a televisio~
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signal and are distributed throu~h the LTFB periods of the
signal. ~or practical purposes one or two ~B periods
per field are suf~icient.
For synchronising the receiving equipment~ the
portions of data may be transmitted after a run-in signal,
for example of 8 identical bitso
'~ypical data signals are in the form of a run-in, a
start code9 address information (eOg. page nu~er, and
data addres~) command bits~ spare bits and the character
information. Accordingly, the selector equipment
preferably incorporate~ a s-tart code comparison device and
is operable to route information -to the memory device only
when it is accompanied by a correct start code; the clock
circuit o~ the receiver system is responsivs to the run-
in and tran~itiorl~ in the data waveform and -the system
incorporates address~responsive means for correctly
positioning the segments~ ~he selector may have an
input for a code indicative of the required channel and ~
a comparator operable to pass only si~rnals of that ~ -
channel.
A sy~tem as provided by the presen-t invention may
simply be provided in such a form as to provide, on a ~;
television receiver, a visual display from information
transmitted during periods when no video signal is
being transmitted on a television channel to which the
receiver is tunsd. ~he viewer may then cause the video
si~nal, the characters from -the character generator, or
both~ to be displayed upon the screen of the receiver as
required. It is, howeverg within the scope of the
invention to arrange -Shat the memory device can be fed
wi~h information transmitted during the non-video periods
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of ano-ther television channel or even -transmitted
independently of any video signal over a separate data
channel~ ~uch separate data channel may be a telephone
ol other cable network or a radiation and receiver system.
Problems of synchronisation may be minimised by providing
adequate data storage capacit~ at the reception point.
A separate data channel of low band width can be
acceptable if data is transmitted for an adequate
proportion of the time.
It is greatly advantageous -to employ a memory device
of the continuously recirculating or other cyclically
accessible type, such as a randorn access memory cyclically
addressed. ~l`he stored information can then be fed to the
chara¢ter ~enerator repeatedly after the memory device has
beerl filled for continuous or repeated display~ even after ;'
transmission of the information has ceased. ~urin~ normal
operation, the memory device stores the in~`ormation from
the selected channel and allows it to be displayed when- ;
.. , :
ever required and continuously for as long as required~
even though the tran~mission of th~t channel is inter-
mittent (e.g. as in the case of one page selected from a
set of 50).
~ or practical purposes, the character information is
normally transmitted in the form of binary si~nals.
Satisfactory results under good conditions of reception
such as are normally found within the main service area
of a television broadcast transmitter, are obtainable by
transmi-tting the signals in the simple NRZ (non return to
zero) form where the zero- and one- characters are simply
represented by two different signal levels, one of which
is usually zero. ~or improved reception under difficult
`~. ......
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~v~
conditions, eOg. in fringe areas where noise is
significant, the information may be transmitted in
bi-phase ~orm. With this form of transmission~ each l-bit
is represented by a l-level followed by a zero-level and
each zero bit is represented by a zero-level follQwed by a
l~level or vice versa. The rate of transmission of the
information is however approximately halved compared wi-th
the simple NRZ form. The band-width required with bi- ;~ ;
phase transmission is less than twice the bit-frequency. ~ ~
It is a characteristic of bi-phase si~nals that with any -
series of bits (each of which involves a transi-tion
between two levels, even thou~h it may be iden-tical with
the preceding bit)~ the maximum interval between the
transltions can never be longer than the time oocupied by
one bit. Cert~in tran~mission errors are thereEore
recognisable as such. ;~ -
Additional advantage may be taken of the said
characteristic of bi-phase signals by transmittin~ wi-th ~-
every portion of data sent during a video intervalg a code
in which there is at least one interval be-tween transition~
which is greater than the said maximum interval. ~'he
presence of the code with the portions of data received
is at least strongly indicative that the portions of data
are genuine, and not, ~or example~ spurious data generated
by random interference or derived accidentally ~rom some ;
other channel.
A convenient page contains 22 (horizontal) s-trips o~
40 characters. An ~FB period does not conveniently allow
time ~or 40 charac-ters to be transmitted using bi-phase
si~nals, though this is readily achieved usin~ simple N~Z
signals. here~ore, when bi phase signals are used each
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f~
strip may be divided into segments transmitted one in each
L~FB period. With four segments per strip ~transmitted in
~our successive LTFB periods), each page is constituted by
88 segmen-ts for a 22-strip page. '~he data address is in
the form of a segment address, rather than a simple line
address, and operates to position the segments of
characters correctly on the screen.
For use with information received in the form of bi~
phase signals, the selector equipment advantageously has a
pair of data registers arranged so that they are responsive
to store the first and second signal levels of each digit
respectively and is arranged to pass the inforr~lation to the
~emory device only if the data in one re~iste~r is the
compleDIent of the other. In one preferred arr~ngement the
registers of the pair are connected in parallel for -the
~ .
receipt of information and in series at other times.
Co`lveniently, the data registers are operated by a control
logic circuit which arranges them for the receipt of`
informat;on only when a ætart code corresponding with a
selected channel has been received.
In a presently pref`erred form o~ the system, the memory
dovice is arranged to ~-tore -the inf`ormation o~ a single page
selectecl from information corresponding wi-th a series o~
pages received in -turn, and -the reading device i5 operable
25 to read out the page information from the memory device -
repeatedly. Compared with arrangements in which the whole
of the received information in all the channels is stored,
this arrangement is very economic as regards storage '' t
capacity. lt does not give immediate access to a required
~0 page, but this consideration is found to be unimportant
since the cycle time for as mang as 50 pages is small, even
when only one L'l'~B period per field is used~
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7~ ~
As -the character genera-tor, i-t is convenient to
provide a generator of the 7 x 5 matrix type. ~his is a
well know~ -type of device which need not be described in
detail. It suffices to indicate that for the generation
of a line of characters, -the generator must be fed with
the character informa-tion seven -times in seven successive
line periods~
A system as provided by the present inven-tion may be
incorporated in a television receiver, the character
genarator communicating with -the video circuit of the
receiver. Al-ternatively, the character generator may `~
communicate with a modulator to provide a carrier modula-
ted by video si~nals representing the information. '~he
latter arran~ement may be used in an adaptor unit ~or
connection in the aerial cable o~ an existing receiver
so that the receiver may be employed for the present
purpose without in-ternal modification.
~he following description in which reference is made
to the accompanying drawings is given in order -to
illustra-te the invention. In the drawings: -
is a block diagram showing a normal
television receiver modi~ied b~ the
additlon of a sys-tem as provlded by the
invention, and
Figures 2 and ~ are block diagrams showing parts of
the system shown in ~-igure l in ~urther ~ -
detail, and ~ -
_i~ure 4 is a dlagram illustra-ting the form o~ the
da-ta handled~ and
Fi~res 5A, 5B,_5C and 5D relate to a character
rounding system which may advantageously
be employedO
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$7'
Figs. ~, 3 and 4 are concerned with signals of the
bi-phase type and a system for the reception thereof.
~p~ropriately modified apparatus may be provided for use
with signals of the simple NRZ type.
Referring to ~ig. 1, the demodulated television
signal to which the television receiver is tuned is taken
from the receiver 11 at an emitter follo~Jer point. The
signal contain3 6 MHz F/M sound which is ~iltered by ~ilter
120 The signal is then a~plified to provide several feeds
of 75 ohm video.
The sync separator derives 7 ~rom the incoming
demodulated signal, line and field rate timing pulses
which are u3ed in various parts of the system.
One video ~eed ~oes direct to part 3 which for
simplicity ma~ be regarded as a video switch.
A second video ~eed to the video switch goes via a
text adder. The tex-t adder adds a controlled ~mount of
current to this video signal so -that captions are
effectively superimposed on the picture corresponding to
this video patha
A third video feed passes to -the data receiver. The
data receiver is exposed to the whole video si~nal~ and
C~l pick out tho data si~nal~ discriminatin~ agalns-t
normal picture signals. Alternati~ely, the data receiver
might be enabled only during the appropriate time5 when
the data lines occur in the si~nal.
The data receiver presents the data -to the stores of
the Text Signal Generator. rrhis generates the appropriate
text signal a-t logical (Transistor-Transistor Logic)
voltage levels.
rrhe text signal is used to control the text adder and
is also pas~ed via a filter and a converter which chan~es
the signal to 75 Ohm video level. r~his video text signal
then passes to another input of the video switch.
The output of the video switch is either input 1, 2
or 3 in the diagram. r~his passes through an amplifier and
returns the signal -to the luminance channel of the se-t (at
approximately 5 volts peak to peak in this case).
Control of the display i5 effected by pre~sing the ;~
appropriate button on the display selec-tor. Possibilities
are as follows:-
Bu-t-ton Video Switch Out~ut
Picture only Input 1
Picture f text (added) Inpu-t 2
~ic-ture ~ -te~t (non Input 1 and 2 ~whichever
addi-tive)
is instantaneously
greater)
simultaneously
r~ext only (black or white Input 3.
text)
r~he display control ensures tha-t correc-t timing is
maintained as follows.
r~ext is only produced during active line -time
(no-t during line sync pulses)
r~ext is not produced ~uring Pield blankin~. -
r~he video switch always passes -the input 1 to
the ou-tput durin~ line and field sync times~
This ensures that the output always contains -
the correct television synchronisin~ puDses~ `
Black text or white text is effected by either
using normal or inverted polarity text signal under
control from the display selector and display control.
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The display selector also contains a connection -to the set
which enables the sound ou-tput o~ the set to be mutedO
In an alternative arrangement, instead of taking a
de-modulated signal from the television receiver, an
adapter is connected in the aerial lead~ In this case the
input -to the system is at R~Fo '~his is demodulated -to
video and a similar process performed on the video signal
as just describedO The resultant video is then re-
modulated and ~assed to the aerial input of the television
receiver on an appropriate channel.
If data from one television channel is to be dis-
played over another television channel, then a second R.F.
dernodulator is required, one to provide the data~ the
other for the normal television prograln~e.
'I`he sy~tem o~ Eli~ure 1 may be rnodified to include
coloured captions. In thi~ case direct access to -the Red, '''
Green, Blue guns of the television receiver is the
simplest solution. An Ro~ aerial lead adaptor would also
be possible.
'The psrt marked "Data Receiver" in Figure 1 i5 shown
in detail in Fi~ure 2. As shown in L'~ ure 4, the data
format consists of 16 parts of varying len~th excludin~
the run in. After the start code t'he si~nal is in the
form of bi-phase bits and the character signals are in a
standard AS~II code~ -
Referring now to Fi~. 2, the DATA PICK 0F~ and CLOCK
~GENERATOR presents the DA'~A ROUTING CI~CUI~ with -the
da~a and re~enerated clock at standard TTL lo~ic levels~ '
Until a start code has been received the DA'lA
REGI~ ~ ~ and B are connected in series via the DA'~A
ROUTING CIRCUIT and data is continuously shifted througrh
~r . .
,.
r;~ 9
`.j.
the D~'~A REGI~ER~o 'l'he receiver recognises a star-t code
by con-tinuously comparing -the contents of DA'I'A REGIS'~ER B
wi-th the start code applied to -the DATA CO~ARA'~OR via the
COMPARE DA'~A MUL'~IPLEXER. r~he contents of DA'~A REGIS'~RS ~ -
~ and B are also compared in the COMPLEMEN'~ CHECK CIRCUI'
to see if the halves o~ the start code complement each .~ :.
other. When a correct start code has been received the ::
~ON'~XOL LOGIG. will store this and increment the DECODE
COUNTER by 1 which now points to the part of the data ;.
containin~ the line number.
'rhe CON'rROL LOGIG ins-tructs the COMPA~.DA'~A ..
MUL'rIP~EXER.to apply the selected line number to the
~oM~ARA~r~olt and connects the ~A'~A REGIS'rERS A and B in
parallel via the DA'l'~ ROU'~ING CIRCUI'~. A '~WO PHASE CLOCK
15 is applied to the ~A'rA XEGIS'~æRS clocking REGIS'~ER A ~irst ...
and then Bo As a BI-P~IAS~.transmission ~ode is used, the .. - .
~irst element of each bit is shifted into ~A~A REGISTER A
and the ~econd element into B~ '~herefoxe DA~A REGIS'~ER B .
will contain the inverse da-ta of DAr~A REGIS~ER A. ~ .
After the correct start code has been received and
the next 5 bits have been demultiplexed by the two phase
clock action and shi~ted in-to DAr~A REGISr~E~S A and B a
strobe pulse is genera-ted by the BI~ COUNr~ER -to compare the
received data with the selected data label and to check if
the contents of DA~A REGIS~ERS A and B co~lement each
o-ther. If so5 this again is stored in the CON~ROL ~OGIC ~ .
which in turn will increment the DECODE COUN~ER by 1 9
pointing now to the part of the data con-taining the page
.: . .
number, ....
A further 6 bits are demultiplexed and shifted into
the DA~A REGIS~ERS A and B. A strobe pulse is again
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~L O ~ r~
~enerated by the BIT COUN~ER to compare the received data . : :
wi-th the selected page number and to check if the contents
of the -two REGISr~ERS A and B complement each otherO r~his
again is stored in the CON'~ROL ~OGIC which increments the
D~CO~E COUNr~ER by 1, pointing now to the part of the data
containing the strip and segment numbers.
If the correct start code and sel.ected-line and page
number have been received the control logi.c will pass the
next 13 par-ts of the data (96 bits in 12 8-bit groups) on
to the DISPLAY via the OU'~PU'~ DA~A SELEC~'OR and ~AI'A !''~
BUF~EX Sr~ORE. If at any time a complementatio~ error is
found within an 8-bit group, a blank is passed on to the i~
DISP~AY instead o~ the received data within that group.
A~ter the 13 -~art~ have been passed on to the DISP~Y the
control unit will reset, ready to receive another start
code and new d~ta and the cycle is repeated~
Fig. 3 shows further details of the part marked "~ex-t
Signal Generator" in Figure 1. Data is received in the
~orm o~ eight-bit parallel words on an eight wire input
from the data received from the apparatus of ~'igure 20
rl'hese words are presented to the input o~ a segment store
16, con~i~ting o~ eight 16-bit serial-in parallel-out :
shift registers. When each word is presented to the input
o~ the store 16, a strobe pulse is app~iod thus entering ~.
the data. r~welve words are clocked into the store~ the ~ -
first o~ which denotes the row and segment addressO I~
transmission is on two lines per field, two similar
segment stores are required, one for each data line :
re¢eived in the ~ield blanking time.
~'he page store 17 into which -the incoming data is
clocked at the appropriate time consists o~ six 1024-bit
: ''
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shif-t registers. ~his page store then feeds into a strip ~
s-tore which consists of six 40-bit shift registers. ~he ; -
output of -the strip store addresses a character genera-tor
via a blanking generator.
I~ order -to print a chara~,ter on -the television
screen the ~II code for that character must be presented
to the display generator at the appropriate times on the
appropriate lines of the field scan. Since a charac-~r
generator of th~ 7 ~ 5 matrix type is used, this ASCII
character code must be presented to the display generator
seven -times whilst the row number is stepped ~rom 1
through 7. In order to display a strip of ~0 characters
on the screen -the strip store mu,st be rotated 7 time~
(once per ~can line) whil~t th0 row number is s~eppod
from 1 through 7.
For the display of a full page of in~ormation the
page store must be rotated ~ully once per picture field,
but only in steps of 40 characters corresponding -to the
last rotation of the strip store.
In fact the strip store is only actually ro-tated
6 timas and on the seventh row the output of the s-trip
~tore is entered into the fron-t of the page store~
~wenty two strips of characters are generated on the
screen and each of these consis-ts of four segmen-ts.
As the strip store is rotated the seventh time,
segment addresses O through ~ are generated internally
a~d are compared wi-th the inpu-t segment number which
appears a-t the twelfth posi-tion in the line store. ~;
Immediately after each seventh rotation of -the
strip s-tore, a strip number counter is incremented by
one step through tha range 1 to 22 and this is compared
'. :' " :
~,,.
': ; ': '
with the input s-trip address. ~hen strip and segment
address of input data and currently displayed data are the
same, the page store is switched to accept data from the
segment store 16. As soon as the local segment address is
incremented the page store switches ba,ck to accepting data
~rom -the strip store.
When a page of data is initially selecte~ one ~full
rotation of the page store is completed with the blanking
generator switched on, thus emptying the store of the
previous informationO ~he receiver will display a blank
screen until such a time that it receives appropriate new
data from the -text signal generator. ;
r~he extr~me left- and right-hand se~ments of strip 1
of all pages may possess a transparent pa~e number of ~u¢h
oharacter that they are displayed whiohever pa~e is
selected. ~he left-hand segment may contain the page
number actually being transmitted at the particular time,
and the right-hand segment may contain the time of day
accurate to one second.
A character rounding s~stem may be provided for
improved results. In a preferred syste~, the main
characters are generated in a 7 x 5 matrix arrangement and
roun~ing bits of the characters are generated in a 6 x 4
matrix arrangement and superposed in a staggered
arrangement - see ~i~ures 5A and 5C. This system is very i~ ;
¢onvenient with interlaced scanni~g. -
~he results are preferable to those shown in ~igure 5B
obtained with a syst~m which relies upon generating round- ;;
ing bits when diagonals are detected - compare~igures 5
and 5C.
The 7 x 5 and 6 x 4 read only memories (ROn's)
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d~7 : ~ ~
required can be produced by s-tandard integrated circuit - :
manufacturing techniques, ~he two ROM's must be addressed : :; :
. .; . . ..
in an out of step fashion, requiring the iden-ti~ication of
the two fields involved. ~igure 5D shows an example o~ a
circuit for combining the output of the ROM's. .`
Reference has been made herein to symbols in the form
of low definition picture components as an example of . -
graphical symbols which can be transmittedO O~ especial - . :
interest are symbols derived by filling the positions of
a matrix in the various possible combinations. ~ 3 x 2
matrix~ i.e. a matrix having three horizontal rows with .
two positions in each gives 62 possible graphical symbols
derived by inserting from 1 to 5 dots in various
distribution~ in addition to tht possibilities of a `;
completely full and a comp:letely empty matrix wh.ich a:re to
be regartled as two further grclphical symbols. Using
symbols of this type arranged, like alpha-numeric symbols .
on a series of lines, still pictorial matter can be formed.
. .
'~he character generator of the present equipmen-t is there- ..
fore usefully arranged -to generate such graphical symbols,
instead.of alpha-numeric symbols, ln response to . ~ :
~'~propriate commands received with the transmission. .-
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