GB2237420A - Computer terminal apparatus - Google Patents

Abstract

Computer terminal apparatus for receiving teletext transmissions or other peripheral device data comprises a computer terminal PC and a teletext decoder TD or other peripheral device preferably interconnected by an RS-232 interface, one or more of the usual control couplings, eg DCD, RI, of the interface being used to afford control information relating to and discriminating the data and status messages of the teletext or peripheral device data for use by the PC applications software for affording an enhanced performance. <IMAGE>

Description

DESCRIPTION COMPUTER TERMINAL APPARATUS This invention relates to computer terminal apparatus comprising a computer terminal, and a computer peripheral device coupled to said computer terminal for the exchange of data and status messages therebetween under the control of applications software of said computer terminal. The invention has particular application to computer terminal apparatus in which the computer peripheral device is coupled to the computer terminal using an RS-232 interface or other suitable coupling and also to computer terminal apparatus in which the computer peripheral device takes the form of a teletext decoder.

Teletext decoders are known for use in or with a receiver which is suitable for receiving teletext transmissions of a type in which coded data pulses are transmitted in a television signal in television lines where no picture signals representing normal picture signal are present e.g. in the field or vertical blanking interval. Teletext decoders are also known for use in or with receivers which are suitable for receiving commercial data services such as the BBC DATACAST teletext service and the IBA AIRCALL teletext service, and which outputs data to a compatible PC or other computer. Such teletext decoders may also be able to receive normal domestic teletext transmissions such as the BBC CEEFAX service and the IBA ORACLE service.

In teletext decoders of the latter type, the PC or other computer to which the teletext decoder is coupled operates under the control of applications software in order to implement the required service, and the required teletext data is fed to the PC or other computer for processing. In order to provide for an improved arrangement, it would be useful to provide the PC or other computer to which the teletext decoder is coupled with status or other control information regarding the teletext data which is being sent to it, but a major problem exists with certain interfaces including the RS 232 in that the PC or other computer has no means of differentiating between the data signals and the status or other control information and treats all received signals in the same way.

It is an object of the present invention to provide an improved form of computer terminal apparatus as aforesaid, whereby the applications software of the computer terminal is able to differentiate between data and status messages.

The present invention provides a computer terminal apparatus comprising a computer terminal, and a computer peripheral device coupled to said computer terminal for the exchange of data and status messages therebetween under the control of applications software of said computer terminal, characterised in that said computer peripheral device includes means for affording a first and a second information signal to said computer terminal indicative of the data or status messages applied thereto by said computer peripheral device, said first information signal in a first state indicating to said computer terminal that either a data message or a status message related to a data message is present and in a second state indicating that a further status message is present whilst said second information, when said first information signal is in its first state, differentiates between the presence of said data message or said data related status message, said first and second information signals being used under the control of said applications software for controlling the operation of said computer terminal.

In one preferred arrangement according to the present invention, the computer terminal and said computer peripheral device are coupled using an interface of the RS-232 standard. The first information signal may then conveniently be applied to said computer terminal by means of the Data Carrier Detect (DCD) coupling of said RS-232 interface, and the second information signal may conveniently be applied to said computer terminal by means of the Ring Indicator (RI) coupling of said RS-232 interface. As an alternative the coupling may be by way of a different interface such as a programmable peripheral interface and a multi-bit bus.

In another preferred arrangement according to the present invention, said computer peripheral device takes the form of a teletext decoder, conveniently adapted to receive commercial teletext data services under the control of said applications software, in which case said status control signal may take the form of a status header signal.

Exemplary embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a block schematic diagram of computer terminal apparatus in accordance with the present invention incorporating a teletext decoder, and Figure 2 is a modification of the diagram of Figure 1.

In the drawing there is shown a block schematic diagram of computer terminal apparatus which consists of a personal computer PC to which is coupled a teletext decoder TD. The teletext decoder TD comprises an input for an aerial A for receiving a teletext transmission, the aerial input being connected to a television tuner T (typically a Philips type U744) which affords an output to an intermediate frequency stage IF (typically a Philips integrated circuit type TDA 2541). The demodulated video signal VS from the intermediate frequency stage IF is applied to a video processing circuit VP (typically a Philips integrated circuit type SAA 5231) which performs, among other things, data slicing for retrieving serial teletext data pulses D from the video signal VS. The video processor VP also produces data clock pulses C and line sync pulses S from the video signal VS.The data pulses D together with the clock pulses C and line sync pulses S are fed to a data acquisition and control circuit DAC, which is preferably a Philips integrated circuit type SAA 5250. The data acquisition and control circuit DAC operates on the serial teletext data pulses from the video processor VP and converts them into parallel data bytes which are stored in a dedicated first-in, first-out random access memory M1 (typically at 2K x 8 bit), via a multi-bit bus B1.

The data acquisition and control circuit DAC is operated under the control of a microprocessor MP (typically an Intel integrated circuit type 8031) via a multi-bit bus B2, the microprocessor MP being interconnected with a random access memory M2 via a further multi-bit bus B3. In Figure 1 the microprocessor MP is coupled to the PC by means of a standard RS-232 interface I. The RS-232 or EIA RS-232 as it is otherwise known is the Recommended Standard Number 232. Revision C from the Engineering Department of the Electronics Industries Association, standard use of the RS-232 being given in "C Programmer's Guide to Serial Communications" by Joe Campbell, published by Howard W. Sams & Company of Indianapolis, U.S.A. in 1983. As an alternative the V24 standard of the C.C.I.T.T. could be used for the interface I and which is almost identical to RS232.

In normal operation of the arrangement which has been described, the PC would be provided with applications software which would enable the required teletext service to be requested, for example, the BBC DATACAST commercial data service, and would cause the selected service to be displayed on the PC display. One problem with such an arrangement is that due to the data and control messages having a corresponding number of bits (e.g. 8 bits) there is no means of the PC ascertaining, for example, whether the teletext decoder TD has received a valid command or whether the decoder TD has been able to acquire the requested service. Although with conventional systems it is possible to provide this information, due to the use of the RS-232 interface the PC cannot differentiate between actual data messages and status or other control messages which may be used to convey additional information relating to the data messages which the applications software of the PC could use to provide enhanced facilities.

It has now been appreciated that where computer peripherals are connected to a PC or other computer using the RS-232 interface, some of the couplings which are provided for specified control functions in specific modes of operation, for example the Data Carrier Detect (DCD) coupling on pin 8 and the Ring Indicator (RI) coupling on pin 22, are not utilised and could be used for communicating status or other control information regarding the actual signals which exist on the "Transmitted Data (TD)" pin 2 and "Received Data (RD)" pin 3 couplings on the RS-232 interface. The pin number given relates to the use of the RS-232 interface with 25 way D-type connectors, see Table 5.5 on page 133 of the book "C Programmer's Guide to Serial Communications" mentioned above.

In this way it would be possible for the PC to interpret whether data or status/control messages are being sent to it from the teletext decoder TD. Also status signals could be generated in the teletext decoder TD in order to convey to the PC an indication as to whether the information conveyed on the RD coupling are data or status/control messages.

This is achieved in the computer terminal apparatus hereinbefore described with reference to Figure 1 by making use of the RS-232 interface I between the microprocessor MP and the PC and by causing the DCD coupling thereof to be activated (logic "1") when data messages or a status header message related to that data are being sent to the PC and de-activated (logic "0") when other control messages such as status reply are being sent to the PC. In addition use is made of the RI coupling to differentiate between the data and status messages to the PC in accordance with the following truth table: TABLE DCD RI "1" "O" Data message "1" "1" Status header message "O" "X" Status reply message.

The precise form that the status header message takes is dependent upon the particular teletext service being used and also on whether an "ASCII" format (7 bit characters + possible 1 bit parity) or "BINARY" format (8 bit byte) is used for transmitting the status messages. ASCII format headers are for general applications and are intended for human or computer interpretation.

Binary format headers are intended to be specifically machine readable and are coded in a more efficient binary form than the ASCII format headers. Typical examples of both for these formats are given below:1. ASCII Format A sequence of 7 bit ASCII characters.

1.1. Level 1 Teletext Page num err Short Form: p < qhhe alternative: E num textflags err Extended form: p < qhh > X < hhhhhhhhXh < e) alternative: E Either 6 or 15 7 bit ASCII characters in total.

The standard short form could be used to transfer a standard display format level 1 teletext page as a fixed block of data representing teletext packets 0 to 24 inclusive plus packet 27 with any packet in the page not acquired replaced by a corresponding packet containing ASCII SPACE (20 hex) characters.

The extended form could be used to transfer teletext pages in variable length blocks of teletext data possibly additionally containing one packet 28 and up to 16 packet 26's. In this case packets not acquired (as indicated by the packet flags) would not be transferred at all.

Character I ASCII hex I Function 1 "P" 70 1 Indicates Level 1 Teletext Page 12 (q) 1 30 - 37 1 Teletext Magazine number I3-4 < hh? 30 - 39 l 41 - 46 Teletext Page Number 5 "x" 78 Indicates whether teletext page to I be transferred in "short/standard" or on "extended" form. In this case "x" indicates short format.

6 "e" or "E" 65 or 45 "e" indicates no GRC error check word found or CRC error check passed "E" indicates CRC error check word found (in packet 27) and CRC error check failed ie there is an error in the level 1 teletext page

Character ASCII hex Function 1 "p" 70 Indicates Level 1 Teletext Page 2 < q > 30 - 37 Teletext Magazine number 3-4 < hh > 30 - 39 41 - 46 Teletext Page Number 5 "x" 58 Indicates whether teletext page to ------ ----------- ------- ------- ---------- --- be transferred in "short/standard" I I or "extended" form. In this case I "X" insicates extended format. 30 - 39 Teletext Packet flags indicating 41 - 46 which teletext packets have been 6 < h > ditto @ @ @ pk@@ acquired within the page. 1 Each "h" represents 4 bits. Each "pk < n?" represents a packet row address number. 3 2 1 0 6 (h) ditto O 0 0 pk28 I 7 < h > ditto pk27 pk26 pk25 pk24 8 < h > ditto pk23 pk22 pk21 pk20 9 < h > ditto pk19 pk18 pk17 pk16 10 < h > ditto pk15 pk14 pk13 pk12 11 < h > ditto pk11 pk10 pk9 pk8 12 < h > ditto pk7 pk6 pk5 pk4 13 < h > ditto pk3 pk2 pk1 pk0 Each flag bit indicates the presence of the respective packet number in the page (packets could be output in increasing row address number order) eg < pk28 > = 1 indicates presence of packet 28 in next teletext page, pk26 = 1 indicates presence of one or more packet 26's as defined in 14 14 < h > ditto This flag together with pk26 in 7 indicates the total number of packet 26's acquired within the page up to a total of 16 eg if pk26 = 1 & BR< character 14 = "0" then 1 packet 26 was acquired. 3 2 1 0 pk263 pk262 pk261 pk260 15 "e" or "E" 1 65 or 45 "e" indicates no CRC error check I word found or CRC error check passed "E" indicates CRC error check word found (in packet 27) and CRC error check failed ie there is an error in the level 1 teletext page

eg: plOOxe: Page 100 short format level 1 teletext page no error or no CRC found.

p29AxE: Page 29A short format level 1 teletext page with CRC error.

p696X1DFFFFFF3e: Page 696 extended format level 1 teletext page with the following packets present: 28; 27, 26, 24; 23, 22, 21, 20; 19, 18, 17, 16; 15, 14, 13, 12; 11, 10, 9, 8; 7, 6, 5, 4; 3, 2, 1, 0; 4 packet 26's acquired. No CRC error.

1.2. Multi-Packet or Scrambled Teletext Page P < qhh > rC < qh > L < phh > e or -----------------------------------------------------------------------alternative: R E A total of 13 ASCII characters.

Character I ASCII hex I Function 1 "P" I 70 1 Indicates Scrambled Teletext Page 2 < q? 30 - 37 Teletext Magazine number 3-4 < hh > 30 - 39 41 - 46 Teletext Paze Number 5 "r" or "R" 72 or 52 Repeat Flag: "r" indicates that I the page is new or not repeated. "R" I indicates that the page is a repeat I of the last page received. I 6 "C" 43 Continuity index: a 7 bit number I < q) 30 - 37 which increments upon every new page 8 < h 30 - 39 received.

41 - 46 9 "L" 4c Data Length : a 10 bit number gives 10 (p > 30 - 34 . the total length in 8 bit bytes of 11-12 (hh) 30 - 39 the data block contained within the 41 - 46 scrambled page.

13 "e" or "E" 65 or 45 CRC error check: "e" indicates CRC I check passed; the page data is error free. "E" indicates the page data I contains an error.

eg: P704rC3AL400e: Page 704 scrambled teletext or "multi-packet" page. This page is a "new page, continuity 3A hexadecimal, data length = 400 hex (1024 bytes) and the data is error free.

P5AFRC2BL023E: Page 5AF multi-packet page, a repeat of the previously acquired page, continuity = 2B hex, data length = 23 hex (35 bytes) the data contains error(s).

1.3. Independent Data Line or Packet 31 I#nhhhhhh#RC#hh#L#mh#E alternative: r e Total can vary from 10 to 16 ASCII characters.

Character I ASCII hex I Function 1 "I" 49 Indicates Level 1 Teletext Page 2 #n# 30 - 33 Packet 21 channel number (similar to magazine number.

3-8#hhhhhh# 30 - 39 Packet 31 address (similar to page 41 - 46 number) variable from 0 to 6 4 hit I nibbles most significant digit first * "r" or "R" I 72 or 52 Repeat Flag: "r" indicates that the t packet is new or not repeated. t "R" indicates the packet is a repeat of the last packet received.

* "C" 43 Continuity index: an 8 bit number I * < hh > 30 - 39 which increments upon every new I 41 - 46 1 packet acquired.

* "L" 4C Data Laneght: a 6 bit number gives * #m# 30 - 32 the total length in 8 bit bytes of * #h# 30 - 39 the data block contained within the 41 - 46 packet (36 bytes decimal maximum). 1 * "e" or "E" 65 or 45 CRC error check: "e" indicates CRC 1 check passed; the packet data is error free. "E" indicates that the packet data contains error(s). I * Byte number depends upon length of address.

eg: I36RC43L20e: Packet 31, channel = 3, address = 6, a repeat, continuity = 43, data length = 20 (32 bytes decimal) no CRC error.

IOFFFFFFrCABL1DE Packet 31, channel = 0, address = FFFFFF, a "new" packet, continuity = AB hex, data length = 1D hex, CRC error.

Note general notation; < mnpqh) denotes ASCII hex number as follows: 0#h#F ie 30 to 32 hex ------------------------------------------------------------------ Byte Function ------------------------------------------------------------------ 7 0 < h < F ie 30 to 39 and 41 to 46 hex 2. Binary Format: These are output as a series of 8 bit binary bytes and whilst similar to the ASCII format are compressed for greater efficiency.

2.1. Level 1 Teletext Page Short Format (3 bytes in total):

Binary Bits 7 6 5 4 3 2 1 0 1 0 1 1 1 0 mag2 magl mag0 Prefix "01110" binary I gives "p" for magazine zero.

"mag" = 3 bit I magazine number I 2 num7 num6 num5 num4 num3 num2 num1 num0 "num" = 8 bit page number page.

3 0 err 0 0 0 0 0 O bit 7 = short format err = CRC error flag err = O no CRC error I or no CRC error check I received.

err = 1 CRC error in ------------------------------------------------------------------ Extended Format (7 bytes in total):

Byte Function Binary Bits 7 6 5 4 3 2 1 0 1 0 1 1 1 0 mag2 mag1 mag0 Prefix "01110" binary gives "p" for magazine zero.

"mag" = 3 bit magazine number 2 num7 num6 num5 num4 num3 num2 num1 num0 "num" = 8 bit page number 3 1 err 0 pk28 pk27 pk26 pk25 pk24 bit 7 = extended format err = CRC error flag err = 0 no CRC error or no CRC error check received.

err = 1 CRC error in page.

4 pk23 pk22 pk21 pk20 pk19 pk18 pk17 pk16 Each pk#n# indicates 5 pk15 pk14 pk13 pk12 pk11 pk10 pk9 pk8 the presence of the 6 pk7 pk6 pk5 pk4 pk3 pk2 pk1 pk0 packet address in the page similar to ASCII format.

7 0 0 0 0 p263 p262 p261 p260 p26#n# similar to ASCII format pk26#n#.

eg: Byte Value Function 76543210 1 0 1 1 1 0 0 0 1 Level 1 Page, magazine = 1 2 0 0 0 0 0 1 0 0 Page number = 04 3 0 0 0 0 0 0 0 0 Short format, either no CRC error or no CRC check.

1 0 1 1 1 0 1 1 1 Level 1 Page, magazine = 7 2 0 1 0 0 1 0 0 1 Page number = 49 3 1 1 0 0 1 0 0 1 Extended format, CRC error Packets acquired: 27, 24 4 1 1 1 1 1 1 1 0 23 - 17 inclusive 5 0 1 1 1 1 1 1 1 14 - 8 inclusive 6 1 0 1 1 1 1 1 1 7, 5 - 0 inclusive 7 0 0 0 0 0 0 0 O no packet 26's.

2.2. Scrambed Teletext Page 5 bytes in total:

-------------------------------------------------------------------------- Binary Bits I Function 7 6 5 4 3 2 1 0 1 0 1 1 1 0 mag2 mag1 mag0 Prefix "01010" binary gives "p" for magazine --------------------- zero.

"mag" = 3 bit I magazine number 2 num7 num6 num5 num4 num3 num2 num1 num0 "num" = 8 bit page number 3 0 con6 con5 con4 con3 con2 con1 con0 "con" = 7 bit continuity index 4 rep err 0 0 0 DL10 DL9 DL8 rep = repeat flag err = CRC error flag err = O no CRC error I 5 DL7 DL6 DLs DL4 DL3 DL2 DL1 DLo DL = 10 bit data length eg: Byte Value Function 76543210 1 0 1 0 1 0 1 1 1 Scrambled page magazine = 7 2 0 0 1 0 0 1 0 0 Page number = 24 3 0 1 0 0 1 1 1 0 Continuity index = 4E hex 4 0 1 0 0 0 1 0 0 Not a repeat, CRC error 5 0 0 0 0 0 0 0 0 Data Length = 400 hex (1024 bytes) 2.3 Packet 31::

Byte Byte I Function I Binary Bits 7 6 5 4 3 2 1 0 ----------------------------------------------------------------- 1 1 1 0 AL2 AL1 AL0 CH1 CH0 Prefix "110" binary with AL = 2 & CH = 1 gives "I" AL = address length CH = channel number 2 AD17 AD16 AD16 AD14 AD13 AD12 AD11 ADl0Address byte 1 tO to 3 Address bytes)l * con7 con6 cons con4 con3 con2 conl con0 "con" = 8 bit j continuity index I * rep err DLs DL4 DL3 DL2 DL1 DLo rep = repeat flag CRC error flag err = O no CRC error IDL = 6 bit data length * depends upon number of address bytes AD as dictated by address length AL.

eg: Byte Value Function 76543210 1 0 1 0 0 0 1 1 1 Packet 31, address length = 1 Channel = 3 2 0 0 0 0 0 1 1 1 Address = 7 (as address length is odd number ignore most significant nibble) 3 1 0 1 0 0 0 0 1 = repeated packet, no CRC & data length = 33 (21 hex) "Teletext Status Headers" are intended for application specifically within teletext docoders where the teletext data is to be transferred to apparatus external to the decoder for further processing or display. Such headers are short sequences of either 7 bit ASCII characters or 8 bit binary bytes which precede each block of teletext data to be transferred. The use of Teletext Status Headers improves the control and flexibility of teletext data transfer from a teletext decoder to an external device.

Note that any header may be prefixed by carriage return, line feed or newline sequence and ASCII SOH 01 hex control code (Start Of Header) or just an SOH control code. Headers may also be terminated by carriage return, line feed. This could be implemented to assist application software required to interpret Teletext Status Headers.

As an alternative to using an interface such as to the RS-232 or V24 standard between the PC and the microprocessor MP, a programmable peripheral interface PPI (typically an Intel integrated circuit type 8255) would be connected, as shown in Figure 2, to the multi-bit bus B3 and to a further multi-bit bus B4 which connects to the PC. Typically the PC would see in the teletext decoder TD two 8-bit registers one of which would be used for all data and status messages and the other of which would be used for the status and control signals in a similar way as with the "DCD" and "RI" signals in the RS-232 interface. Corresponding components between Figures 1 and 2 are indicated by like reference symbols.

Although described in relation to computer terminal apparatus embodying a teletext decoder, it should be appreciated that the principles of the present invention are considered to be applicable to computer terminal apparatus embodying other forms of computer peripheral equipment.

From reading the present disclosure, other modifications will be apparent to persons skilled in the art. Such modifications may involve other features which are already known per se and which may be used instead of or in addition to features already described herein. Although claims have been formulated in this application to particular combinations of features, it should be understood that the scope of the disclosure of the present application also includes any novel feature or any novel combination of features disclosed herein either explicitly or implicitly or any generalisation or modification thereof which would be apparent to persons skilled in the art, whether or not it relates to the same invention as presently claimed in any claim and whether or note it mitigates any or all of the same technical problems as does the present invention. The applicants hereby reserve the right to formulate new claims to such features and/or combinations of such features during the prosecution of the present application or of any further application derived therefrom.

Claims (8)

CLAIM(S)

1. Computer terminal apparatus comprising a computer terminal, and a computer peripheral device coupled to said computer terminal for the exchange of data and status messages therebetween under the control of applications software of said computer terminal, characterised in that said computer peripheral device includes means for affording a first and a second information signal to said computer terminal indicative of the data or status messages applied thereto by said computer peripheral device, said first information signal in a first state indicating to said computer terminal that either a data message or a status message related to a data message is present and in a second state indicating that a further status message is present whilst said second information, when said first information signal is in its first state, differentiates between the presence of said data message or said data related status message, said first and second information signals being used under the control of said applications software for controlling the operation of said computer terminal.

2. Apparatus as claimed in Claim 1, characterised in that said computer terminal and said computer peripheral device are coupled using an interface according to the RS-232 standard.

3. Apparatus as claimed in Claim 2, characterised in that said first information signal is applied to said computer terminal by means of the Data Carrier Detect (DCD) coupling of said RS-232 interface.

4. Apparatus as claimed in Claim 2 or 3, characterised in that said second information signal is applied to said computer terminal by means of the Ring Indicator (RI) coupling of said RS-232 interface.

5. Apparatus as claimed in Claim 1, characterised in that said computer terminal and said computer peripheral device are coupled using a programmable peripheral interface and a multi-bit bus.

6. Apparatus as claimed in any preceding claim, characterised in that said computer peripheral device takes the form of a teletext decoder.

7. Apparatus as claimed in Claim 6, characterised in that said teletext decoder is adapted to receive commercial teletext data services under the control of said applications software.

8. Computer terminal apparatus substantially as hereinbefore described with reference to the accompanying drawing.