Method for automatically controlling optimal tuning point for receiving teletext

Abstract: Method for automatically controlling the optimal tuning point for receiving teletext increases or decreases the tuning point by steps of a certain frequency for the byte error at each step tuning point to be detected and memorized so that the tuning point for the minimal byte error is found to provide the optimal tuning frequency for receiving a teletext, thus eliminating the inconvenience of manipulating a key to find the optimal tuning point from the display on a TV screen. The system of the method employs a microprocessor and a teletext processor in addition to the tuner.

Description: BRIEF SUMMARY OF INVENTION This invention relates to a method for automatically controlling the optimal tuning point for receiving broadcast teletext, in particular, a method in which the tuning point is increased or decreased by certain steps for the byte error at each step tuning point to be detected and memorized so as to find the tuning point for the minimum byte errors and memorize it for providing the optimum tuning frequency for teletext receiving. Herefore, the user desiring a teletext service has been using a closely controllable Up/Down key to bring up or down the tuning point and visually confirm the number of byte errors from the display on a television screen to select the tuning point for receiving the broadcast teletext. The conventional system however has a disadvantage of spending much time to determine the optimum tuning point for receiving broadcast teletext in addition to the inconvenience of complicated processes. Further, the method for visually determining a tuning point by means of manipulating a closely controllable Up/Down key results in a consequence of imprecision in determining the optimal tuning point. Without setting a tuning point for teletext receiving the teletext service becomes impossible to obtain, let alone the quality of screen display. The number of errors per 1000 bytes must be less than 5. JP-A-63215178 describes a teletext receiver build in television. In such a television an adjustment of a television tuner is automatically obtained by controlling the local oscillation frequency of the television tuner on the basis of a detection output from a teletext data error rate detecting circuit so that an error rate is reduced. However, starting from an arbitrary frequency, the frequency is increased or decreased such that the adjusted frequency has a reduced error rate. This error rate, on the other hand, is not compulsoryly the optimum value since the control might be trapped in a local minimum. The present invention set out in the appended claim, therefore, is designed to eliminate the above stated disadvantage and provides the optimum tuning point automatically by the input of an optimum tuning point memory key. BRIEF DESCRIPTION OF DRAWINGS Fig. 1 shows a block diagram of an automatic optimum tuning point control system for receiving teletext on a television receiver according to the invention; Fig. 2 shows a flow sheet of an automatic optimal tuning point control system of the invention; Fig. 3 shows an operational flow sheet of a teletext processor with an input of the teletext mode switch key according to the invention. Numerals in the drawings indicate the following; Numeral 1 indicating a key matrix section, 2 a microprocessor, 3 a tuner, 4 an image signal processor, 5 an image signal switching section, 6 a CRT, 7 a teletext processor, 8 an OR Gate. DETAILED DESCRIPTION In reference to the drawings, the invention shall be described in details. According to the construction of the block diagram shown in Fig. 1, a microprocessor 2 which controls the operation of the whole system under the output signal of a key matrix section applies channel selection data SD through a tuner 3 to an image signal processor 4, as input Vi, whose output Vo applies through an image signal (R, G, B) switching section 5 to a CRT 6, while the output RG of a microprocessor 2 and the output RB of a teletext processor 7 apply via an OR Gate 8 to an image signal switching section 5. The microprocessor 2 and the teletext processor 7 connect to each other with TxD (Transmit Serial Data), RxD (Receive Serial Data) and CLOCK for serial data mutual transmission. Referring to Figs. 2 and 3, the operation of the invention shall be described in detail, as follows. Being applied with a signal on pressing a memory key of the automatic optimal tuning point on the key matrix section, the microprocessor 2 determines the signal to be a signal or not from the memory key of the automatic optimal tuning point and, if it is for the optimal tuning point, B register stores the current tuning frequency to memorize the current channel tuning point and A register stores '0' and clears the counter to apply RxD and CLOCK signals for the teletext processor 7 to execute a check program (byte error detection routine) for teletext receiving. The microprocessor 2 then delays for a time T to receive from the processor 7 the input number of byte errors TxD stored for the time T as the result of executing the check program for teletext receiving rate and (according to the CLOCK signals) stores the current counter value and the number of byte errors in stacks (memory) to add '1' to the current value of the counter. Thereafter, the value of A register is determined to be '0' or not and, if '0', the current tuning frequency is added with a frequency in steps to be set as the value of the current tuning frequency. Vhen the added current tuning frequency does not exceed a boundary frequency 0 of arbitrary setting, A register stores '0' and the microprocessor 2 instructs the teletext processor 7 to execute the check program for receiving rate and repeat the process of detecting and memorizing the value of byte errors per step for the corresponding tuning frequencies increased by step-by-step method. If the added current tuning frequency exceeds the boundary frequency 0 of arbitrary setting, A register is set for detection of byte errors of the steps and the original tuning frequency (the value of B register) is stored as the current tuning frequency for the microprocessor 2 to instruct through RxD and CLOCK to the teletext processor to execute the check program for receiving rate. Thereafter, the process of detecting and memorizing the value of byte errors per step for the corresponding tuning frequencies increased by the step-by-step method is repeated. Also, when the microprocessor 2 determines the value of A register to be '1', the current tuning frequency is reduced by the frequency of the predetermined step to be set as the value of a current tuning frequency. When the reduced current tuning frequency does not exceed the boundary frequency '1' of arbitrary setting, the process of detecting and memorizing the value of byte errors per step is repeated for the tuning frequencies reduced by the step-by-step method. However, when the reduced current tuning frequency exceeds the boundary frequency '1' of arbitrary setting, the above Process for repeating is interrupted for the exceeding frequency to be compared with the number of byte errors saved on the stacks and determine the value of minimum byte errors, whose counter value is used to count the current tuning frequency and transmit it to the teletext processor 7. Upon executting the above process, the microprocessor 2 makes the value of B register to be memorized as the current tuning frequency and transmit the value of the tuning frequency to the tuner 3. According to the subroutine of the teletext processor 7 operating on input of the teletext mode switch key, as shown in Fig. 3, the microprocessor 2 upon receiving an input for switching from TV mode to teletext mode by a key of the key matrix section 1 transmits the signal from the key to the teletext processor 7, which finds the memory for the automatic optimal tuning. point following the input signal of the switch key and, if found, transmits the memory found to the microprocessor 2. Thus, a teletext service is provided for a viewer with the setting of the optimal tuning frequency. The present invention stores the optimal tuning frequency for receiving a teletext to eliminate the inconvenience of finding the optimal frequency, and it also provides accurate tuning frequencies for teletext receiving to enhance the reliability of the current teletext service.

Claims: Method for automatically controlling the optimal tuning point for receiving teletext, the method being characterized in that the current tuning frequency is increased or decreased by arbitrary frequency steps within the limits of a frequency band between boundary frequencies of arbitrary setting in order to detect byte errors per each arbitrary frequency step, and that the tuning frequency corresponding to the minimum value of byte errors at the time of detection is memorized in the teletext processor (7) or microprocessor (2), to be used as the tuning frequency for switching from the TV mode to the teletext mode in order to receive teletext.

Inventors: HO CHANG DONG, HO CHANG, DONG
Applicants: GOLD STAR CO, GOLDSTAR CO. LTD.
Application year: 1990
Main classification: H04N5
IPC codes: H04N5, H03J7, H04N7, H04N9