GB2051527A - Method and apparatus for transmission of non-alpha numeric characters to a television receiver - Google Patents

Abstract

For transmission of non-alpha numeric, e.g. ideographic, text to a TV receiver in "Teletext" or "Viewdata", the transmitted signal consists of conventional data lines of coded signals indicating characters of a set stored within the decoder of the TV and of additional data lines each indicating the dot matrix pattern of a character (as in Fig. 1) to be transmitted and displayed which is not stored within the decoder. Within the decoder the additional data lines are stored and then accessed for display instead of those in the character generator therein. Control signals governing colour etc. may be included. <IMAGE>

Description

SPECIFICATION Method and apparatus with a transmission of non-alpha numeric characters to a television receiver The specification relates to a method of, and apparatus for, the transmission of non-alpha numeric characters to a television receiver.

Teletext and Viewdata are two known systems enabling the transmission of information to a television receiver in which the transmitted information is displayed. In both systems pages of information are transmitted to the receiver as a series of coded signals each representing one line of the page to be displayed. It is usual with alpha numeric systems to have 24 lines each of 40 characters to form a page. In the Teletext system each line is broadcast as a coded signal in the interval occupied by otherwise unused data lines of a broadcast T.V. signal during the field blanking interval allowed for the flyback prior to each active field transmission. In the Viewdata system transmission is via telephone lines enabling an interactive link to be established between the user and the information source but substantially the same form of signals are used.

With both systems the coded signals identifying the 40 characters in each line are fed serially to a decoder in the T.V. receiver in which they access a character generator storing all the characters to be displayed. The characters so accessed are then displayed on the T.V. screen. A typical Teletext data line comprises 45 bytes each 8 bits long. The first 5 bytes of each Teletext data line comprise synchronisation information, framing information, and identify magazine and line numbers in a Hamming code. The last 40 bytes each uniquely identify the address of one of the character sets stored in the character generator within the decoder.

Further description of the known Teletext system can be found from the Broadcast Teletext Specification published in September 1976 jointly by the B.B.C., I.B.A. and B.R.E.M.A.

In any system utilising alpha numeric characters a total of some ninety-six different characters (letters, numerals and graphic symbols) need to be accessable to provide an intelligable information display. Each character may be uniquely defined by an 8 bit coded signal and a total of less than 8K bits of storage are needed in the character generator.

With non-alpha numeric languages, for example the Chinese language, in which ideograms are used, significantly greater storage capacity is required.

In the Chinese language there are the total of some 50,000 ideograms. Adequate display of each ideogram requires at least a 1 6 x 1 6 dot matrix. If a Teletext system following the principles of the known alpha numeric system were to be used for a language including ideograms such as the Chinese language a total storage capacity in excess of 1 2M bits would be required. Attempts have been made in the past to provide a Teletext system for ideographic languages which treat each page of information as a two dimensional display. It has been found with such systems that the access time for each page to be displayed is significantly longer than is acceptable.

Objects of the present invention include the provision of a method of, and apparatus for, transmitting non-alpha numeric characters to a T.V. receiver, which overcomes or alleviates the problems of the known systems.

According to one aspect the invention provides a method of transmitting non-alpha numeric characters to a television receiver in which data lines of coded signals are transmitted to a decoder within a television receiver in which decoder those coded signals access a character generator containing a subset of the full character set to be transmitted and displayed and in which additional data lines may be transmitted which additional data lines each uniquely define the pattern of a character to be transmitted and displayed which is not included in the character subset contained in the character generator.

According to a second aspect the invention provides a system for transmitting non-alpha numeric characters to a T.V. receiver comprising means for generating data lines of coded signals, means for transmitting those data lines to a decoder within a T.V. receiver, means within the decoder enabling the received signals to access a character generator containing a subset of the full character set to be transmitted and displayed, and a means operable to generate further additional data lines each defining the pattern of a character to be transmitted and displayed which character is not included in the subset accessible in the character generator.

According to a third aspect the invention provides a method of encoding non-alpha numeric characters for transmission to a decoder within a television receiver comprising loading character addresses into predetermined byte locations of a data line and including the steps of interrogating a first memory containing a subset of the characters to be transmitted and, if the character is located in the first memory loading the address of that character into a predetermined byte location, and if the character is not in the first memory interrogating a further memory to obtain a dot matrix pattern of the character to be transmitted, writing the dot matrix pattern of the character to be transmitted into a selected additional data line and writing the address of the selected additional data line into the predetermined byte location.

According to a fourth aspect the invention provides an encoder for forming coded data lines to enable the transmission of non-alpha numeric characters to a television receiver and including input means enabling a character to be transmitted to be input to the encoder, means enabling interrogation of a first memory containing a subset of characters to be transmitted to locate the input character and, if the input character is in the subset, to load the address of a character in a predetermined byte location of a data line to be transmitted, and, if the input character is not in the first memory to interrogate a further memory to obtain signals indicative of the dot matrix pattern of the character, means enabling the signals indicative of the dot matrix pattern of the further character to be written into a selected additional data line and means for writing the address of the selected additional data line into the predetermined byte location of the data line to be transmitted.

According to a fifth aspect the invention provides a decoder for receiving data lines of coded signals indicative of non-alpha numeric characters, the decoder comprising receiver means, first store means operable to store the addresses of characters held in a second store means within the decoder and to store additional data lines, control means operable to control the accessing of characters in the second store means using addresses held in the first store means and to access addressed data lines stored in the first store means and to provide signals enabling display of the selected characters.

Other features of invention will become apparent from following description which is made with reference to the accompanying drawings and in which: Figure 1 shows a 16 6 > c X 16 dot Matrix defining an ideogram; Figure 2 shows, schematically an encoding system embodying the present invention; Figure 3 is a flow chart of the encoding operation; Figure 4, illustrates the data lines transmitted; Figure 5, illustrates in detail part of one of the data lines transmitted; Figure 6, shows, schematically a decoder embodying the present invention; and Figure 7 is a flow chart of the decoding operation.

As has been noted above the known alpha numeric Teletext system provides a page of 24 lines of information, each line containing a maximum of 40 characters to be displayed.

The display of Chinese ideograms requires more space on the T.V. screen and analysis has shown that a maximum of 14 lines each containing a maximum of 1 8 characters can be displayed if the information is to be readily discernable by a viewer.

Analysis of the Chinese language shows that not all the 50,000 ideograms in it are in common use. A Chinese typewriter for example usually can type only 3,000 characters. Of these 3,000 most commonly used characters approximately 1 ,000 are in common everyday use. The present invention provides for transmission of the addresses of each of 1014 characters stored in a decoder within the T.V.

receiver with the optional transmission of up to 10 extra characters per page by transmission of signals defining the dot matrix of them.

The 3,000 most commonly used Chinese characters can each be displayed by use of a 1 6 x 1 6 dot matrix as illustrated in Fig. 1.

The accessing of the addresses of the 1014 most commonly used characters stored in the decoder, each comprising a 1 6 X16 dot matrix, requires a storage capacity of less than 256K bits.

The system of the present invention provides that the first 14 lines of each page of the Teletext data system carries encoded information detailing the addresses of given ones of 1024 Chinese characters stored in the decoder whilst the next ten lines each send, in an encoded format, the dot matrix of others of the 3,000 characters not held in store in the decoder.

An encoding system in accordance with the present invention is shown in Fig. 2, Fig. 3 shows a flow chart of the encoding operation, Fig. 4 examples of the data lines transmitted by the encoding system and Fig. 5 an example of a double byte in a data line of Fig. 4.

As can be seen from the Figures each data line to be transmitted by the system comprises 45 data bytes each comprising 8 bits of information. The structure of a double byte is shown in Fig. 6 to comprise 1 6 bits aO-a7, bo-b7 of which bits a7, b, are parity bits.

Bytes 1 to 5 include synchronisation, framing, magazine and line encoding information.

Bytes 6 and 7 of the line 0 define the page number to be transmitted and bytes 8 and 9 control information (as will be described in more detail below). Bytes 6 to 9 inclusive of lines 1 to 1 3 include control information and bytes 10 to 45 of lines 0 to 13 comprise 18 double bytes each pair defining the address of a location within the decoder storing the 16 x 16 dot matrix of one of the 1014 character set stored therein. Bytes 6 to 37 of lines 14 to 23 are grouped in pairs each double byte possibly identifying one row of a 1 6 X 1 6 matrix defining a character not included in the 1014 character set stored within the decoder.

To encode a page to be sent; first the page, magazine and line numbers are selected and loaded into bytes 4, 5, 6, and 7 of line '0'.

Control information to be explained in more detail below is loaded into bytes 8 and 9 of line '0' and then the information to be dis played is loaded into the remaining 36 bytes.

The first character to be typed on the key board 30 (see Fig. 3) is fed to a processor 31.

Processor 31 interrogates a core memory storing the 1014 set of the most commonly used characters of the Chinese language. If the character input to processor 31 is located in memory 32 the character is displayed on display 33 whilst the address of the character in memory 32 is loaded into bytes 10 and 11. A character count is then incremented.

The next character fed to the processor 31 causes that processor again to interrogate the memory 32 and, if it is in memory 32, the character is displayed on display 33 whilst its address is loaded into bytes 1 2 and 1 3 of line 0. The character count is again incremented.

This process continues until the characters count equals 18 or until a character is fed to processor 31 which is not in memory 32.

When the character count reaches 18 the line count is incremented by 1 and the character count reset to zero. It should be noted that when feeding information to line 1 the page number is not loaded into bytes 6 and 7. All four of bytes 6, 7, 8 and 9 are available for control functions. Loading of the character addresses into the bytes of lines 1 to 1 3 continues as described above.

If the character input to processor 31 is not located in memory 32 the processor 31 selects the next available line n of the data lines 14-23, and loads into the corresponding bytes of the data line a code identifying that selected line n and reads into the selected line n the dot matrix forming the character. The first row of the character being defined by bytes 6 and 7 of the selected line n, the second row by bytes 8 and 9 and so on until the sixteenth row of the character is read into bytes 36 and 37. No control information is loaded into lines 14 to 23, bytes 6 to 37 inclusive of these lines carry signals defining one of the optional characters not included in the memory 32. It should be noted that bytes 38 to 45 of lines 14 to 23 are not used.

As soon as ines 0 to 1 3 are completed the line count indicates that the page has been completed.

A table giving the codes identifying the lines 14 to 23 is as follows:- TABLE I Codes identifying lines 1 4 to 24: Line No. Character address 14 0000001110 15 0000001111 16 0000010000 17 0000010001 18 0000010010 19 0000010011 20 0000010100 21 0000010101 22 0000010110 23 0000010111 24 0000011000 The codes loaded into bytes 8 and 9 of line 0 and bytes 6 to 9 of lines 1 to 1 3 provide that the display may be modified in accordance with desired input. The various control functions which may be used are defined by the first five least significant bits of the first byte of each pair. Table II indicates the control functions which may be obtained.

TABLE II Possible Control Functions Obtainable aoa'a2a3a4 Control Function 01000 not defined 01001 red ideogram 01010 green ideogram 01011 yellow ideogram 01100 blue ideogram 01101 magenta ideogram 01110 cyan ideogram 01111 white ideogram 10000 not defined 10001 flesh/steady 10010 double/single width 10011 start/end box 10100 black background 10101 new background 10110 hold/release graphics 10111 conceal display 11000 not defined 11001 red graphics 11010 green graphics 11011 yellow graphics 11100 blue graphics 11101 magenta graphics 11110 cyan graphics 11111 white graphics To enable the transmission of graphic symbols falling outside the 3,000 character set the following encoding philosophy is adopted:: In the character mode, if a0 = a, = 0, the bits a4a5a,bOb,b2b3b4b5b6 are used to address the character generator, identifying uniquely one of the 1024 characters.

In the graphics mode, if aO= a1 = 0, the bits a2a3a4a5a6bOb1b2b3b4b5b6 identify a graphics code occupying one character space as follows: b6b5b4b3 b2b1 bOa6 a5a4a3a2 If either of a0 and a, is non-zero, aoa'a2a3a4 forms a 5-bit control code. The control function which will take effect from the current character as listed in Table II.

At the beginning of the line, the control function is reset to White ideogram; steady; single width; end box; black background and release graphics. The control functions identified by aoa'a3a4 = 10001 or 10010 or 10011 or 10111 identifies a change to the complement of the current state.

In the graphics mode, if either a0 or a, is non-zero, a space is displayed in the corresponding character position. In the character mode, if either a0 or a, is non-zero, an ideogram will be displayed, with address given by bits Oa5a6bOb,b2b3b4b5b6. Thus 512 characters can be addressed whilst utilizing a control function. This allows abrupt changes in the display format and is essential because, unlike the English language, there is not a space between two ideograms.

The first character location of line '0', i.e., the 8th and 9th bytes, and the first 2 character locations of lines 1 to 13, i.e., the 6th, 7th, 8th and 9th bytes, are not displayed.

They are used only as control codes so that the appropriate display modes can be selected at the beginning of the line.

Referring once again to Fig. 2 the information loaded into the various bytes of each data line are held in store 34 until required for transmission. It will be appreciated that a plurality of pages of information, each comprising up to 24 data lines, may be held in store 34 and be transmitted continuously.

Operation of the decoder apparatus in a T.V. receiver, as shown in Fig. 6, comprises the functions of writing data into the decoder's memory (during the field of blanking intervals) and reading the data from that memory out to display on the T.V. screen.

Operation of the decoder shown in Fig. 6 will be described with reference to the flowchart of Fig. 7. During the field blanking interval the transmitted data lines are written into the decoder enabling the desired information to be displayed subsequently. The apparatus into which the signals are read comprise data acquisition and logic circuitry (DALC) 51, an oscillator 52, counters 53 and 54, a decoder input keyboard (DIK) 55, page comparator circuitry (PCC) 56, a 1 6 X 1 K bit random access memory (RAM) 57, and address demultiplexer and memory control circuitry (ADMCC) 58. The data line contained in the composite video signal fed to the television receiver is converted into transistor-transistor logic (TTL) compatible logic levels.

In each data line received there are, as already described, 45 data bytes each comprising 8 bits of information. Bytes 1 and 2 of each data line synchronise the oscillator 52 such that the output of oscillator 52 is locked onto the incoming data stream.

The incoming data stream is converted into a 1 6 bit words using a serial-in-parallel-out SIPO register in the DALC 51.

Counter 53 divides the clock output from oscillator 52 by 1 6 during reception of data.

Counter 54 is incremented each time counter 52 resets unless counter 54 is reset or disabled.

In each data line counters 53 and 54 are held at reset until the framing code appears (as the most significant 8 bits coming from SIPO in DALC 51-from byte 3). At this moment and at subsequent moments when counter 53 resets the output of SIPO in DALC 51 is shifted into a parallel-in-parallel-out (PIPO) register forming a 16 bit output of DALC 51.

In operation a user would key in a three digit magazine and page number using DIK 55 and this is stored in PCC 56. The writing of the received signal into RAM 57 will subsequently be enabled only if the received signal includes a page and magazine number coded signal matching with that stored in PCC 56.

When the count on counter 54 is 1 the 4th and 5th bytes of the data line will be available. These two bytes contain the magazine and line number (in Hamming code) the magazine number stored in DALC 51 is updated.

The line number is also stored in DALC 51.

Counter 54 is reset to 0 when counter 53 next changes from 1 5 to zero. Once this has happened counter 54 counts the number of 16 bit words in a data line.

If the line being received is line 0 the page number stored in DALC 51 is updated by the information contained in the 6th and 7th bytes of the data line (that is to say when the output of counter 54 is zero). A page match register will be set or reset in dependence upon whether or not a match exists between the magazine and page numbers then stored in the PCC 56 and DALC 51.

The write logic will be enabled as long as the page match register is and the magazine number of the subsequent data lines (lines 1 to 24) are the same, that is to say until a new line '0' including a fresh page address is received by the decoder.

As counters 53 and 54 are incremented data is written into the RAM 57 from the output of DALC 51 each time the output of counter 53 changes from 1 5 to zero. The output of counter 54 identifies the number of the character that is to be written in any data line. For example when counter 54 counts 1 it will means that the 1 6 bit word defining the second character of the line is to be written into RAM 57 from bytes 8 and 9 of the data line. The address in the RAM 57 is given by the five bit output of the line number count held in the DALC 51 and the five bit output from counter 54. When counter 54 reaches 20 the write logic is disabled until the next data line is received. Counters 53 and 54 are reset and the receiver is enabled to receive another data line.It will be appreciated that the various lines forming a page need not be received by the decoder in any particular order.

The components of the decoder involves in display operations are the oscillator 52, the counters 53 and 54, counters 59 and 60, address demultiplexer and memory control circuits (ADMCC) 58 and 61, RAM 57, a 16 X 16K bit read only memory (ROM) 62, control decoders and registers (CDR) 63 and a multiplexer and parallel to serial converter (MPSC) 64.

Oscillator 52, when displaying information runs at a nominal 6 MHz and is synchronised by the line synchronisation pulses of the T.V.

receiver. Counters 53 and 54 control the horizontal timing of the display. Counters 59 and 60 the vertical timing of the display.

Counter 53 divides the clock input from oscillator 52 by 1 7 and is used to clock data into the display. Thus one of the 1 6 rows in a character dot matrix pattern (16 by 16) will be displayed as counter 53 increments from 0 through to 1 5. A space will be displayed when counter 53 reaches 16, this being the spacing between two adjacent characters on a horizontal line. The number of the character currently being accessed is identified by the counter 54. Counter 54 is incremented whenever counter 53 changes from 1 6 to zero.

Counter 59 is incremented by the line synchronisation pulses to identify one of the 1 6 rows of the character dot matrix being displayed; a space is displayed when counter 59 reaches 16, being the space between adjacent lines of characters. Counter 60 is incremented when counter 59 changes from 1 6 to Zero to identify one of fourteen horizontal lines of characters.

The page of characters to be displayed are in fact displayed within a window on the television screen. To display the text within this window the display will be enabled on each field after scan line 32 or 345 (in a 625 line T.V. system). Counters 59 and 60 are first reset and then enabled by field pulses generated by the oscillator 52. Counter 60 is reset for a second time as it counts 2 momentarily. The display is then enabled and the memory will be accessed starting from this scan line.

In the horizontal direction counters 53 and 54 are reset and disabled by the line synchronisation pulses A. Monostable will be triggered by the line synchronisation pulses to give a delay of about six micro-seconds after which counters 53 and 54 are enabled. When counter 53 reaches 1 data will be read from the RAM 57, the address accessed within RAM 57 being given by counter 60 (which identifies the line number) and by counter 54 (which identifies the character location within the line).

The data stored in any pair of bytes comprises 1 6 bits a0a1a2a3a4a5a6a7b0b1b2b3b4b5b6b7. Of these bits a7 and b7 are parity bits and will be left out from the following description.

The data read from the RAM 57 will contain control bits a0 and a,.

a0 = a, = O. If both a0 and a1 are zero the bits a4a5a6bOb,b2b3b4b5b6 give the character address for one of the 1024 characters stored within ROM 62 or within the temporary storage in RAM 57. If a4a5a6bOb,b2b3b4b5b6 is one of those listed in Table II i.e. in the range 0000001100 to 0000011000 the character is in fact an optional character temporarily stored in RAM 57. RAM 57 will then be accessed for a second time when counter 53 counts to 9. The address accessed in RAM 57 being given by the bits b2b3b4b5b6 and the five bit output of counter 59.

If a4a5a6bOb,b2b3b4b5b6 is not one of those listed in Table I the character is in a permanent location in ROM 62. ROM 62 will be accessed when counter 53 reaches 9, the address being given by the ten bits a4a5a6bOb,b2b3b4b5b6 and the four bits given by the least significant four bits of the output of counter 59.

a0 7 Q or a, 7) O. If either a0 or a1 is non zero the bits aoa'a2a3a4 give a control code to alter the display style according to Table II.

The control code will update control registers in CDR 63 when counter 53 nexts resets to zero. The control registers are reset to their initial values by the line synchronisation pulses. The bits a5a6bOb,b2b3b4b5b6 give the character address for one of five hundred and twelve characters which again may either be stored temporarily in RAM 57 or permanently in ROM 62. The address of these characters is contained in the nine bit character address.

If a5a6bOb, b2b3b4b5b6 is one of 000001110 through 000011000 the character is an optional character temporarily stored in RAM 57. RAM 57 will be accused for a second time when counter C reaches 9, the address being given by b2b3b4b5b6 and the five bit output of counter 59.

If a5a6bOb,b2b3b4b5b6 is not one of 000001110 through 000011000 the characters stored permanently in ROM 62 which is accessed when counter 53 reaches 9. The address being given by Oa5a6bObrb2b3b4b5b6 and the least significant four bits of the output of counter 59.

The data read from either RAM 57 or ROM 62 is loaded into the MSPC 64 when counter 53 next resets to zero. On the next clock pulse from oscillator 52 the information is shifted from converter 64 to CDR 63. Thus when the horizontal character count given by counter 54 is n the (n + 1 )th character is being read from memory (RAM 57 or ROM 62) and the nth character is being shifted from the MSPC 64 to CDR 63.

In addition the decoder provides that the first two characters in a line are not displayed.

The display will only be enabled when the horizontal character count given by counter 54 is between 3 and 20. When counter 54 reaches 20 both counters 53 and 54 are reset to zero and disabled when 53 next changes from 1 5 to 0 and the display is again disabled.

The serial data from the multiplexing and parallel to serial converter circuitry 64 is modified to give the various display styles and finally to give the three red-green-blue output to drive the T.V. display.

At the foot of the display window counters 59 and 60 are reset and held disabled when counter 60 reaches 1 4. This will disable the display and await for the beginning of the next field.

Claims (16)

1. A method of transmitting non-alpha numeric characters to a television receiver, in which data lines of coded signals are transmitted to a decoder within a television receiver in which decoder those coded signals access a character generator containing a subset of the full character set to be transmitted and displayed, and in which additional data lines may be transmitted which additional data lines each uniquely define the pattern of a character to be transmitted and displayed which is not included in the character subset contained in the character generator.

2. The method of Claim 1, in which the character patterns of the additional data lines are initially stored in the decoder and accessed as part of the character generator.

3. A method according to Claim 1 or Claim 2, in which the data lines of coded signals transmitted to the decoder also include control signals operational to control the way in which the information is displayed.

4. A system for transmitting non-alpha numeric characters to a T.V. receiver comprising means for generating data lines of coded signals, means for transmitting those data lines to a decoder within a T.V. receiver, means within the decoder enabling the received signals to access a character generator containing a subset of the full character set to be transmitted and displayed, and a means operable to generate further additional data lines each defining the pattern of a character to be transmitted and displayed which character is not included in the subset accessible in the character generator.

5. A system according to Claim 4, in which the additional data lines are received by the decoder and stored therein, that portion of the storage of the decoder being accessed as part of the character generator.

6. A system according to Claim 4 or Claim 5, in which the data lines of coded signals include control signals and in which the decoder includes means for decoding these control signals and to vary the way in which information is displayed by the T.V. receiver.

7. A method of encoding non-alpha numeric characters for transmission to a decoder within a television receiver comprising loading character addresses into predetermined byte locations of a data line and including the steps of interrogating a first memory containing a subset of the characters to be transmitted and, if the character is located in the first memory loading the address of that character into a predetermined byte location, and if the character is not in the first memory interrogating a further memory to obtain a dot matrix pattern of the character to be transmitted, writing the dot matrix pattern of the character to be transmitted into a selected additional data line and writing the address of the selected additional data line into the predetermined byte location.

8. An encoder for forming coded data lines to enable the transmission of non-alpha numeric characters to a television receiver and including input means enabling a character to be transmitted to be input to the encoder, means enabling interrogation of a first memory containing a subset of characters to be transmitted to locate the input character and, if the input character is in the subset, to load the address of a character in a predertermined byte location of a data line to be transmitted, and, if the input character is not in the first memory to interrogate a further memory to obtain signals indicative of the dot matrix pattern of the character, means enabling the signals indicative of the dot matrix pattern of the further character to be written into a selected additional data line and means for writing the address of the selected additional data line into the predetermined byte location of the data line to be transmitted.

9. An encoder according to Claim 8, in which interrogation means comprises a processor, the first memory comprises a core memory and the second memory comprises an external memory accessible by the processor.

10. A decoder for receiving data lines of coded signals indicative of non-alpha numeric characters, the decoder comprising receiver means, first store means operable to store the addresses of characters held in a second store means within the decoder and to store additional data lines, control means operable to control the accessing of characters in the second store means using addresses' held in the first store means and to access addressed data lines stored in the first store means and to provide signals enabling display of the selected characters.

11. A decoder according to Claim 10 in which the first store means comprises a random access memory and the second store means a read only memory.

1 2. A television receiver including a decoder according to Claim 10 or Claim 11.

1 3. A method of encoding information enabling the transmission of non-alpha numeric characters in a data line substantially as here it before described with reference to Fig. 3.

14. Apparatus enabling the encoding of data lines to enable the transmission of nonalpha numeric characters substantially as hereinbefore described with reference to Fig.

2.

1 5. A decoder substantially as hereinbefore described with reference to Fig. 6.

16. A method of decoding data lines substantially as hereinbefore described with reference to Fig. 7.

1 7. A method of transmitting non-alpha numeric characters to a television receiver substantially as herein before described.

1 8. A system enabling the transmission of non-alpha numeric characters to a television receiver substantially as hereinbefore de scribe.