JPS6254270B2 - - Google Patents

Description

[Detailed Description of the Invention] Technical Field The present invention relates to a data transmission system using a code transmission method in which character data is converted into a character code and transmitted, and this is reproduced on the receiving side using a code memory and a character generator. The present invention relates to a method for handling errors in received data.

BACKGROUND TECHNOLOGY Teletext transmission systems currently being developed in Japan include a pattern transmission system and a code transmission system. In the pattern transmission method, the teletext screen information is first decomposed into scanning lines. The signal is then converted into a digital signal (binary NRZ signal) of "0" and "1" for each pixel, and is broadcast while being superimposed on the vertical blanking period (VBL) of the television video signal. Information such as color and program number is also encoded and sent together. In the receiver, the received signal is written as is into the display memory, and the information is displayed on the receiver. On the other hand, in the code transmission method, the information on the screen to be sent is changed to a character code (ASCII, JIS, etc.) for each character, and as in the pattern method, it is converted to a binary NRZ signal, which is superimposed on VBL and sent. The receiver reads the character pattern corresponding to the character from the character generator (ROM), writes it into the display memory, and displays it. Even in the code transmission method, when sending a figure, the pixel information is sent.

As mentioned above, teletext signals are transmitted by being superimposed on the vertical blanking period of the television video signal, and the basic unit (data packet) is a series of signals superimposed on one horizontal scanning period. . A data packet consists of a header section followed by an information data section. The header section transmits basic information necessary to demodulate the digital signal, such as ensuring synchronization of the digital signal and the type of signal in the information data section.
The information data section transmits information regarding the character screen configuration. FIG. 1 shows the data format of a packet in a fixed data format experimental code transmission system in which the positions of transmitted data and display characters on a CRT are determined. Data for one screen is transmitted using a page control packet, external character pattern packet, display control packet, character code packet, etc. The page control packet transmits the program code for selecting a program, the page code, the screen display control code for updating and deleting the screen, the number of packets that make up one screen, the number of external characters to be used, etc. control the reception and display of The external character pattern packet transmits pattern data for one standard character in two packets. The display control packet controls the coloring, flashing, console, etc. of each character, and instructs the types of standard characters, enlarged characters, and continuous mosaic. A character code packet transmits a character code of 8 standard characters in 2-byte codes and 16 characters in small characters in 1-byte code in one packet.

By the way, in the case of the pattern transmission method, errors in signal transmission are simply pixel errors, but in the case of the code transmission method, they are errors in the characters and figures themselves, so the following signal error detection is required. A method is being adopted. That is, the data is an (8,4) extended Hamming code, and a CRC (Cyclic-Redandanoy-Code) is added to the page control packet to improve error detection ability.

In teletext broadcasting using the code transmission method currently under development, if a signal error is detected using the signal error detection method described above, further processing is forcibly stopped (screen display is stopped). Processing was fixed.

DISCLOSURE OF THE INVENTION The present invention stores processes to be performed when there is an error in received data in a memory for each type of error, and executes one of the plurality of processes.
It is an object of the present invention to provide an error processing method in which a selection is made in advance for each type of error by an external switch means, and the selected processing is performed in the event of an error.

As a result, the present invention allows the user to arbitrarily set the processing to be performed in the event of an error in data, creating a flexible and expanded system for, for example, teletext broadcasting.

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below with reference to drawings of embodiments. FIG. 2 is a circuit diagram of a main part of a decoder for teletext broadcasting to which the error processing method of the present invention is applied. _T1 is a terminal through which a character signal separated from the video detection output of the television receiver is input to the buffer memory. Reference numeral 2 denotes an MPU (microprocessor) provided in the decoder, which performs data processing, error processing, display control, etc. on the character signals stored in the buffer memory 1 using various control signals. 3 is an error processing program ROM that stores the error processing program shown in FIG. 4 is an error handling program ROM that stores a program for displaying on the screen even if there is a CRC error in a page control packet; 5 is an error handling program ROM that stores a program for displaying on the screen even if a packet is dropped; This is an error handling program ROM that stores a program to display the screen even if there is a Hamming code error.
Switches SW ₁ , SW ₂ , and SW ₃ correspond to error processing program ROMs 4, 5, and 6, respectively, and when any switch is turned on in advance, "1" data is stored in a predetermined register of MPU 2, and the corresponding This is an error processing selection switch which executes the contents of the error processing program ROM during error processing by the error processing program ROM3, and when turned off, stores "0" in the register and stops subsequent processing. 8 is the error handling selection switch 7.
This is the interface circuit for MPU2. 9 is
An image display memory 10 stores patterns corresponding to characters and figures in the buffer memory 1 read out by the MPU 2, and an image display memory 10 adds a chromaticity signal and a luminance signal to the data in the image display memory 9 to obtain R, G, and B output signals.
This is an image display control circuit that outputs from terminal _T2 to the video output circuit of the television receiver.

Next, the error handling method of the present invention will be explained based on the flowchart of FIG. First, the error processing selection switch 7 selects the error processing program to determine whether to perform error processing for CRC errors, packet omissions, and Hamming code errors in page control packets, that is, to stop subsequent processing.
Select whether to perform preset processing in ROM4, 5, or 6. In the former case, "0" is set, and in the latter case, "1" is set for each switch SW ₁ , SW ₂ ,
It is stored in a predetermined register in the MPU 2 corresponding to SW ₃ . Then, one packet of data from the buffer memory 1 is read by the MPU 2, and error processing is performed on the read one packet of data according to the flow shown in FIG. Of the three types of errors listed above, the CRC error in the page control packet is the most severe, followed by packet loss and Hamming code errors. Therefore, error checking is performed in this order. If there is no error, the data of the packet is decoded, stored in the image display memory 9, and sent to the image display control circuit 10.
Through this process, characters, figures, etc. are displayed or the display is controlled. When an error occurs, the screen display stops or the screen display stored in the error processing program ROM4, 5, and 6 changes depending on the contents of the registers corresponding to the error processing selection switches _SW1 , _SW2 , and _SW3 . It will be done. Except when the screen display is stopped, the next packet is transferred from buffer memory 1 to the MPU.
2, and the above error processing is repeated.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the structure of a data packet for teletext broadcasting using the code transmission method, Fig. 2 is a circuit diagram of a main part of a decoder of a teletext broadcasting receiver using the error processing method of the present invention, and Fig. 3 is a diagram showing the main part circuit diagram of a decoder of a teletext broadcasting receiver using the error processing method of the present invention. 3 is a flowchart showing the flow of error processing according to the invention. 3, 4, 5, 6...Error handling program
ROM, 7...Error processing selection switch, 2...
MPU.

Claims (1)

[Claims] 1 Convert character data to character code and transmit it,
In a code transmission data transmission system in which data is reproduced by a code memory and a character generator on the receiving side, the process to be performed when there is an error in the received data is stored in the memory for each type of error. An error handling method characterized in that one of these plurality of processes is selected in advance for each type of error by an external switch means, and the selected process is performed in the event of an error.