GB2240679A

GB2240679A - Method of selecting receiving frequency in RDS receiver

Info

Publication number: GB2240679A
Application number: GB9101995A
Authority: GB
Inventors: Koichi Kasa; Reisuke Sato; Kiyoshi Izumi; Akira Hayama; Yoshiro Kunugi; Hitoshi Kawabata
Original assignee: Pioneer Electronic Corp
Current assignee: Pioneer Corp
Priority date: 1990-01-31
Filing date: 1991-01-30
Publication date: 1991-08-07
Anticipated expiration: 2011-01-30
Also published as: GB9101995D0; DE4102919C2; DE4102919A1; GB2240679B

Abstract

A frequency selecting method in an RDS receiver capable of storing frequency and program identification (PI) data of network stations. The PI data of the currently selected station is compared with the PI data of a second station, chosen on the basis of the frequency data, for determining coincidence with the exception of area code. When this is detected the second station is selected. <IMAGE>

Description

'I C -7 9FE3 METHOD OF SELECTING RECEIVING FREQUENCY IN RDS RECEIVER The

present invention relates to a method of selecting the receiving frequency in a receiver for the Radio Data System (referred to as RDS receiver hereinafter).

The RDS (Radio Data System) broadcasting is a broadcasting service in which, in the program broadcasting of general broadcasting stations, information relating to the broadcast such as information regarding the program content or the like is transmitted as data by a multiplex modulation. The transmitted data is demodulated on the reception side, so that a desired program content can be selected on the basis of the demodulated data, thereby services are offered to radio listeners.

In.the RDS broadcasting, a signal of 57 kHz as a third harmonic of a stereo pilot signal of 19 kHz in a range out of a frequency band of an FM modulation wave is used as a subcarrier. The subcarrier is amplitude modulated into a radio data signal by a data signal, 2 which is treated by filtering and biphase coding, carrying information regarding the broadcasting such as program content and the like, and the amplitude modulated subcarrier is frequency modulated into the main carrier for the broadcasting. Standards of the above broadcasting scheme were proposed by the European Broadcasting Union (EBU).

As will be-clearly understood from Fig. 1 showing a base band coding structure of a radio data signal, in the radio data signal, data of 104 bits are processed as one group and are repetitively transmitted through a multiplex transmission. One group comprises four blocks each having 26 bits. Each block comprises an information word of 16 bits and a check word of 10 bits. Each group is classified into sixteen types, that is, Type 0 through Type 15 indicated by four bits according to the information content. Furthermore, two versions A and B are defined for each of the types (0 to 15).

Figs. 2A and 2B show the format of groups of the types OA and OB, respectively. In the type OA group, program identification data (referred to as PI data hereinafter) of 16 bits consisting of a country code, an area code, and a program code is arranged in a block 1. Various codes such as group type code, version code (B0), traffic information broadcasting station identification 3 (TP) code, program content identification (PTY) code, and the like are arranged in a block 2. Station frequency data (hereinafter, abbreviated as AF data) of network stations broadcasting the same program is arranged in a block 3. Broadcasting station name data (hereinafter, abbreviated as PS data) is arranged in a block 4. on the other hand, in the type OB group (shown in Fig. 2B), only the content of the block 3 differs from that in the type OA group. Specifically, the PI code is arranged in the block 3. That is. the AF data of the network stations is transmitted by only the type OA group. The PS data is transmitted by the type OA and OB groups.

As mentioned above, the AF data of the network stations which broadcast the same program as the program of the broadcasting station which is currently being received is also included in the radio data signal of the type OA group. Therefore, a so-called network follow function described below can be performed. At the time of the reception, the AF data and PI code which are obtained by the demodulation are retrieved and stored as an AF list.. For instance, in the case where a receiving strength of the broadcasting station of the program which is currently being received is decreased due to a disturbance such as the multipath interference or the like, another station in the same network station group -4is selected on the basis of the AF list which has previously been stored. Furthermore, what is called a PI check is made to see if the program which is received in accordance with the AF list is correct or not by comparing the PI codes. Thus, the same program can be listened always in a good receiving state by the network follow function without being influenced by external disturbances.

Since stations having different area codes in the PI data are included in the same network station group, a Regional OFF mode in which the area code is ignored in the PI check operation and a Regional ON mode in which the area code is included in the PI check are defined in the network follow function. In the Regional OFF mode, a station of the same network station group located outside the area in which the first receiving station is located (referred to as other regional station, hereinafter) may be received.

However, if a user of the RDS receiver wishes to positively receive a same network station of another regi,on,-that is, a network station in a region into which the user has entered, such a demand could not be satisfied by the conventional network follow function, and inconveniences have been experienped.

The present invention is based on the recognition of the inconveniences described above and it is an object of the invention to provide a receiving frequency selecting method in an RDS receiver in which a same network station in another region can be positively received.

A method of selecting a receiving frequency according to the present invention is adapted, in an RDS receiver capable of receiving an RDS broadcasting wave on which a plurality of AF data of a same network station group and PI data including an area code are superimposed, for changing the receiving frequency from the currently selected receiving frequency to the frequency of another same network station given by one of the plurality of AF data, the method comprises: a first step of holding PI data obtained by a broadcast wave of the currently selected receiving frequency; a second step of detecting the existence of a receiving station based on the plurality of AF data; a third step of detecting that PI data obtained by the broadcast wave of the receiving station detected in the second step and the PI data-held in the first step coincide with each other excluding the area code; and a fourth step of setting a new receiving frequency to the frequency of the receiving station selected at present if it is detected that the area code in the PI data obtained in the third step is -6not identical with the area code in the area code in the PI data held in the first step.

In the receiving frequency selecting method according to the invention. AF data of the currently selected receiving station Is held in response to a command and, a new receiving frequency is set to the frequency of the receiving station selected at present when the PI data obtained from the broadcast wave of the receiving station and the previously held PI data coincide with each other excluding the area code and the area codes in both PI data are not identical with each other.

Embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings, in which:- Fig. 1 is a diagram showing a base band coding structure of radio data; Z.

Figs. 2A and 2B are diagrams showing formats of group types OA and OB, respectively; Fig. 3 is a block diagram showing a fundamental construction of an RDS receiver to which the receiving frequency selecting method according to the present invention is applied; Fig. 4 is a flowchart showing an example of processing steps of the regional channel selection as an embodiment of the receiving frequency selecting method of the present invention; Figs. 5A and 5B are diagrams showing the arrangement of pairs of AF data respectively according to a method A and a method B of the transmission of the AF data; Fig. 6 is a flowchart showing another example of processing steps of the regional channel selection as a second embodiment of the receiving frequency selecting method of the present invention; Fig. 7 is a flowchart showing processing steps of a subroutine for producing an AP list in a modification of the second embodiment; Fig. 8 is a flowchart showing a further example of processing steps of the regional channel selection as a third embodiment of the present invention; Fig. 9 is a flowchart showing a still further example of processing steps of the regional channel selection as a fourth embodiment of the present invention; and Fig. 10 is a flowchart showing another example of processing steps of regional channel selection as the fourth embodiment of the present invention.

An embodiment of the present invention will be described in detail hereinafter with reference to the drawings.

Fig. 3 is a block diagram generally showing an 2 example of a fundamental construction of an RDS receiver to which the receiving frequency selecting method according to the present invention is applied. In the diagram, an FM multiplexed broadcasting wave received by an antenna 1 is supplied to a front-end 2, by which a desired station is selected and the signal of the selected station is converted into an intermediate frequency (IF)..After that, the signal is supplied through an IF amplifier 3 to an FM detector 4. For instance, the front-end 2 employs a PLL synthesizer system using a PLI, circuit including a programmable frequency divider. A frequency dividing ratio of the programmable frequency divider is controlled by a controller 13 which will be explained later, so that a channel selection operation is performed. A detection output of the FM detector 4 is supplied to an MPX (multiplex) demodulating circuit 5 and is separated into audio signals of the L (left) and R (right) channels in the case of a stereophonic broadcasting. The signals of the L and R channels are provided as reproduced audio output aignals through a muting circuit 18. The muting circuit 18 is on-off controlled by means of the controller 13.

On the other hand, by the transmission of the detection output of the FM detector 4 through a filter 6, i q a subcarrier of 57 kHz, which is amplitude modulated by a biphase coded data signal, that is a radio data signal, is extracted and is demodulated by a PLL circuit 7. The demodulated output is supplied to a digital (D-) PLL circuit 8 and a decoder 9. In the D-PLL circuit 8, clocks for data demodulation are produced on the basis of the demodulated output of the PLL circuit 7. In the decoder 9, the biphase coded data signal as the demodulated output of the PLL circuit 7 is decoded in synchronism with the clocks produced by the D-PLL circuit 8. A locking state detecting circuit 10 detects locking and unlocking states of the D-PLL circuit 8. Locking ranges of the PLL circuit 7 and D-PLL circuit 8 are switch controlled by a detection output of the detecting circuit 10.

Output data of the decoder 9 has the group unit of 104 bits comprising four blocks each consisting of 26 bits as shown in Fig. 1 and is sequentially supplied to a group, block sync & error detecting circuit 11. In the detecting circuit 11, synchronization of the group and block is established on the basis of an offset word of 10 bits which are respectively assigned to the check word of 10 bits of each block. Further, errors in the information word of 16 bits are detected on the basis of the check word. The error detected data is error corrected by an error correcting circuit 12 at the next stage. Thereafter, the error corrected data is supplied to the controller 13.

The controller 13 consists of a microcomputer and adapted to execute the network follow function in the following manner. At first the controller 13 retrieves code information of each block in the radio data which is sequentially input on a group unit basis, that is, radio data information such as the PI data regarding the program content, AF data, and PS data of the broadcasting station which is currently being received and stores those information into the RAM 14. In response to a station selection command from an operation section 15, the controller 13 controls a frequency dividing ratio of the programmable frequency divider (not shown) of the PLL circuit constituting a part of the front-end 2, thereby executing the network follow function.

A level detection circuit 16 is provided to detect a receiving signal level (field intensity) on the basis of the IF signal level in the IF amplifier 3. Furthermore, there is provided a station detection circuit 17 which detects the presence of a receiving station thereby to produce a station detection signal when the IF signal level in the IF amplifier 3 is higher.than a predetermined level and at the same time the detection output signal of the so-called S-curve characteristic in the FM detector 4 is in a predetermined level range. The receiving signal level detected by the level detection circuit 16 and the station detection signal produced by the station detection circuit 17 are supplied to the controller 13.

A processing procedure of a regional channel selection operation which is executed by the processor of the controller 13 when a regional channel selection command is generated in response to a key operation by the user in the operation section 15 will now be described with reference to the flowchart of Fig. 4. It is assumed that this routine is called and executed in response to the regional channel selection command. It is further assumed that AF data obtained by the demodulation of the received broadcast wave has been already retrieved and the AF list of the same network stations as the station currently being received has already been produced in the memory 14.

The processor first retrieves the AF data and PI data-of-the broadcast wave currently being received and stores those data into predetermined regions of the memory 14 (step S1). According to the AF list mentioned above, the processor reads out one of the AF data in the AF list from the memory 14 (step S2). Then the processor 12 turns the muting circuit 18 on, to effect the audio muting (step S3), and supplies the read-out AP data to the PLL circuit (not shown) in the front-end 2 (step S4). At the same time, the processor sets a PLL timer for measuring a time period T1 required for the PLL circuit to be locked (step SS). The AF data supplied to the PLL circuit is set to the programmable frequency divider in the PLL circuit, so that the receiving frequency changes from the current receiving frequency to another frequency of a network station within the period in which the PLL timer times-out.

After the time-out of the PLL timer (step S6), the processor judges the presence or absence of a receiving station by monitoring the station detection signal from the station detection circuit 17 (step S7). If the existence of a receiving station is detected, the processor retrieves the area code in the PI data of the receiving station (step SS). and stores the area code in the PI data into a predetermined region of the memory 14 (step S9). Then. the processor judges whether or not the PI data retrieved this time and the PI data held in step S1 coincide with each other excluding the area code (step S10). When the PI data coincide with each other, the processor further judges whether or not the area code in the PI data retrieved this time differs from the area 13 code in the PI data stored in step S1 (step S11). If the area codes are different from each other, the processor turns the muting circuit 18 off, to cancel the audio muting (step S12).

Through these operations, a broadcast station having a different area code, that is, a same network station of another region is selected from the same network station group as the broadcast station currently being received.

After the muting has been canceled in step S12, the processor sets a regional timer of a certain constant time period T2 (step S13), and monitors the generation of the above-mentioned regional channel selection command from the operation section within the constant time period T2 in which the timer times-out (steps S14 and 15). If the regional channel selection command is not generated before the time-out, the processor finishes the procedure of this routine without executing any further step. If, on the other hand, the regional channel selection command is generated, the'processor goes back to the step S2, to read-out another AF data in the AF list-from the memory 14 according to the content of the AF list, and repeats the procedure described above. Through this procedure, detection is made to judge whether or not the area code in the PI data retrieved this time in step S11 differs from the area code in the 1 it PI data held in step S1, and all of the area code held in step S9 up to the previous time.

More specifically, after one of the same network station group of another region has been selected, the regional channel selection command is generated once more in the constant time period T2, so that another station in the same network station group is selected. By repeating this, operation, a same network station of a desired region can be selected from the same network station group of other regions.

When it is detected in step S7 that no receiving station exists, when it is detected in step S10 that the PI data are different from each other, or when it is judged in step S11 that the area codes coincide with each other, the processor judges whether or not the processes for determining the presence of the receiving station, the coincidence of the PI data with the exception of the area code, and the disagreement of the area code have been completed for all of the AF data in the AF list (step S16). If the judgment have not been completed, the processor goes back to step S2, to repeat the procedure described above. If, on the other hand, the judgments have been completed for all of the AF data in the AF list, the processor reads-out the former AF data stored in step S1 (step S17), and supplies the read-out AF data to the PLL circuit (step S18). At the same time, the processor sets the PLL timer (step S19). After the time-out of the PLL timer (step S20), the processor proceeds to step S12, to cancel the audio muting.

By this procedure, the receiving frequency is brought back to the frequency of the originally received station. Specifically, when the regional channel selection command is generated to perform the selection of a same network station in another region, the receiving station is brought back to the original receiving station when existence of the receiving station is not detected, or when no same network station of another region exists.

In the case of the embodiment described above, only existence of the receiving station is detected (step S7) before the judgment of the coincidence of the PI code with the exception of the area code (step S10) and the disagreement of the area code (step S11). However, it is also possible to arrange the apparatus that, when the existence of the receiving station is detected, the receiving signal level is retrieved from the level detection circuit 16, so that the processor proceeds to step S8 when the receiving signal level is detected to be higher than the set level.

As specifically described in the foregoing, in the 16 receiving frequency selecting method according to the present invention, the PI data of the currently selected receiving station is stored in response to a command, existence of a receiving station based on the AF list is detected, and a new receiving frequency is set to the frequency of the currently selected receiving station when the PI data obtained from the broadcast wave of the currently selected receiving station and the previously held PI data coincide with each other with the exception of the area code, and at the same time the area codes in both PI data are different from each other. By this operation, a same network station of another region can be positively received.

The second embodiment of the frequency selecting method according to the present invention will be described with reference to Figs. 5A to 7 of the accompanying drawings.

Before entering into the explanation of the second embodiment, the method of transmitting the AF data will be described at first. There are two methods (method A and-method B) used for transmitting the AF data. In the case of the method A. the AF data (fl to fn) of network stations broadcasting the same program are transmitted in a manner shown in Fig. 5A for at most.25 stations without regard to the capability of receiving such stations.

17 Specifically, a group of blocks each having the AF data of two broadcast stations is produced, and data in the head of the firsts block is made to represent the number n of the stations, and the blocks are repeatedly transmitted in sequence. In the method B, on the other hand, the AF data (fl to fn) of network stations broadcasting the same program is transmitted in the manner shown in Fig. 5B. Specifically, network stations in a receivable region with a center on a network station are grouped for each of the network stations. The center station and another station in the group is coupled, and the AF data of those two station are formed into one block, so that a block group is produced for each of the group of network stations. A plurality of block groups each obtained in this way are transmitted repeatedly in sequence, with data % indicating the number of stations in each station group being provided in the head portion of the first block in each group. In the method B, the order of the arrangement of the two AF data words in each block is determined according to a regional rule, such that-if-the frequency on the front side is set to be smaller than the frequency in the rear side, to form an increasing series, it represents the same regional stations. On the other hand, if the frequency on the front side and the frequency in the rear side are arranged to form a decreasing series, it represents other regional stations. The selection between the transmission methods A and B is made on the broadcast station's side.

Since the two methods are provided as the transmission method of the AF data, different methods are required for processing the AF data demodulated on the receiving side. Therefore, it is necessary to judge whether the transmission method of the AF data is the method A or the method B. The discrimination between the methods A and B is performed by the processor of the controller 13, in a manner disclosed in Japanese patent application laid-open No. H1-149529, for example.

The processing procedure executed by the processor of the controller 13 when the transmission method of the RDS broadcast wave is the method B will be explained with reference to the flowchart of Fig. 6. It is assumed that this routine is called and executed when the regional channel selection command is generated in response to the key operation by the user through the operation section 15. It is further assumed that AF data obtained by the demodulation of the received broadcast wave of the transmission method B has been already retrieved and the AP list of the same network stations in a group with the station currently being received as a center station has already been produced in the memory 14 in a manner that 19 the AF data of the center station and the AF data of another station are coupled.

The processor first retrieves the AF data and PI data of the broadcast wave currently being received and stores those data into predetermined regions of the memory 14 (step S21). According to the AF list mentioned above, the processor reads out one of the AF data in the AF list from the memory 14 (step S23). The, the processor judges whether or not the arrangement of the AF data is in the form of a decreasing series. If the arrangement is the decreasing series, it means that the same network stations based on the read-out AF data are of another region of the center station. Therefore the processor turns the muting circuit 18 on, to effect the audio muting (step S24). Then, the processor supplies the readout AF data to the PLL circuit (not shown) in the frontend 2 (step S25) and at the same time, the processor sets the PLL timer for measuring the time period Tl required for the PLL circuit to be locked (step S26). The AF data supplied to the PLL circuit is set to the programmable frequency divider in the PLL circuit, so that the receiving frequency changes from the current receiving frequency to another frequency of a network station within the period in which the PLL timer times-out.

After the time-out of the PLL timer (step S27), the processor judges the presence or absence of a receiving station by monitoring the station detection signal from the station detection circuit 17 (step S28). If the existence of a receiving station is detected, the processor retrieves the area code in the PI data of the receiving station (step S29). Then, the processor judges whether or not the PI data retrieved this time and the PI data held in step S1 coincide with each other with the exception of the area code (step S30). When the PI data coincide with each other, the processor further judges whether or not the area code in the PI data retrieved this time differs from the area code in the PI data stored in step S1 (step S31). If the area codes are different from each other, the processor turns the muting circuit 18 off, to cancel the audio muting (step S32).

Through these operations, a same network station of another region is selected from the same network station group as the broadcast station currently being received.

When it is judged in step S23 that the arrangement is in the form of the increasing series, it is judged in step-S28-, it is determined in step S30 that the PI data do not coincide with each other, or when it is determined in step S31 that the area codes coincide with each other, the processor judges if the detections as to whether or not the arrangement of the AF data is in the form of the i j 1 21 decreasing series, whether or not the receiving station exists, whether or not the PI data coincides with each other with the exception of the area code, whether or not the area codes disagrees, have been completed for all of the data in the AF list (step S33). If the detections have not been completed for all data in the AF list, the processor goes back to step S22, to repeat the procedure described above. If the detections have been completed for all of the data in the AF list, the processor readsout the former AF data stored in step S21 (step S34), and supplies the read-out AF data to the PLL circuit (step S35). At the same time, the processor sets the PLL timer (step S36). After the time- out of the PLL timer (step S37), the processor proceeds to step S32, to cancel the audio muting.

By this procedure, the receiving frequency is brought back to the frequency of the originally received station. Specifically, when the regional channel selection command is generated to perform the selection of a same network station in another region, the receivin station is brought back-to the original receiving station when no same network station of another region exists, or when existence of the receiving station is not detected.

In the case of the embodiment described above, one 221 of AF data in the AF list is read-out from the memory 14 together with the AF data of the center station (in step S22, and the determination is made as to whether or not the arrangement of the AF data is in the form of a decreasing series. However, as shown in Fig. 7, it is also possible to arrange the system such that, in the stage of forming the AF list the determination is made. after the AF data forming a pair of AF data have been retrieved (step S41), as to whether or not the pair of AF data is arranged to form of a decreasing series (step S42). If the arrangement of the AF data is in the form of an increasing series, the processor stores the AF data pair into predetermined regions of the memory 14. In the arrangement of the AF data is in the form of a decreasing series, the processor sets a flag indicating such an arrangement (step S44), and subsequently proceeds to step S43, to store the AF data pair into predetermined regions of the memory 14 together with the flag set in step S44. In the case of such an arrangement, it is sufficient to read-out the flag also when one of the AF data in the AF list-and-the AF data of the center station together forminga couple of AF data are read-out from the memory 14, and to determine the state of the flag in step S23.

Furthermore, in the embodiment described above, the existence of a receiving station only is detected in step 23 S28 before detection of the coincidence of the PI data with the exception of the area code (step S30) and detection of the disagreement of the area codes (step S31) for the channel selection of a same network station of another region. It is, however, also possible to arrange the apparatus that, when the existence of a receiving station is detected, the receiving signal level of the receiving station is retrieved from the level detection circuit 16, and the detection of the receiving signal level to be equal to or higher than the set level is performed before proceeding to step S29.

As specifically described above, in the case of the receiving frequency selecting method according to the present invention, when the method B is used for the transmission of the RDS broadcast wave, the PI data of the currently selected receiving station is stored in response to a command, AF data of a block having a relation of decreasing series with respect to the currently selected receiving frequency is selected, and the existence of a receiving station based on the selected AF data is detected. A new receiving frequency is set to the frequency of the currently selected receiving station when the PI data obtained from the broadcast wave of the currently selected receiving station and the previously held PI data coincide with 2-4 each other with the exception of the area code. By this operation, a same network station of another region can be positively received.

A processing procedure of a regional channel selection operation in the third embodiment which is executed by the processor of the controller 13 when a regional channel selection command is generated in response to a key operation by the user in the operation section 15 will now be described with reference to the flowchart of Fig. 8. Also in the case of this embodiment it is assumed that this routine is called and executed in response to the regional channel selection command in the regional OFF mode. It is further assumed that AF data obtained by the demodulation of the received broadcast wave has been already retrieved and the AF list of the same network stations as the station currently being received has already been produced in the memory 14.

The processor first retrieves the AF data, PI data and PS data of the broadcast wave currently being received and stores those data into predetermined regions of the memory 14 (step S51). According to the AF list mentioned above, the processor reads out one of the AF data in the AF list from the memory 14 (step S52). Then the processor turns the muting circuit 18 on, to effect the audio muting (step S53), and supplies the read-out AF data to the PLL circuit (not shown) in the front-end 2 (step S54). At the same time, the processor sets the PLL timer for measuring the time period T1 required for the PLL circuit to be locked (step S55). The AF data supplied to the PLL circuit is set to the programmable frequency divider in the PLL circuit, so that the receiving frequency changes from the current receiving frequency to another frequency of a network station within the period in which the PLL timer times-out.

After the time-out of the PLL timer (step S56), the processor judges the existence or absence of a receiving station by monitoring the station detection signal from the station detection circuit 17 (step S57). If the existence of a receiving station is detected, the processor retrieves the area code in the PI data of the receiving station (step S58). Then, the processor judges whether or not the PI data retrieved this time and the PI data held in step S1 coincide with each other excluding the area code (step S59). When the PI data coincide with each other, the processor further retrieves the PS data of the receiving station (step S60), and judges whether or not the PS data retrieved this time and the PS data stored in step S51 (step S61) totally coincide with each other.

The broadcast station name is expressed at most by 26 eight alphabetic letters. As shown in Figs. 2A and 2B, the PS data of at most eight digits representing the broadcasting station name is transmitted on group unit basis for the amount of two letters (8 bits x 2) in the OA group or OB group. The data for the amount of 8 letters is transmitted by the transmission of four groups of the radio data signal. The transmitted PS data is treated by the demodulation process in the receiving side, so that the data is displayed as the broadcast station name by at most eight alphabetic letters. Since the broadcast station name differs depending on the region (broadcast area). Therefore, the PS data is different among different regions.

Therefore, when the comparison for determining the total coincidence of the PS data in step S61. it can be determined that a same network station of a region other than the original station is received by judging the condition of disagreement. If the disagreement of the PS data is detected in step S61, the processor turns the muting circuit 18 off, to cancel the audio muting (step S62)-. Then the processor finishes the process of this routine without executing any further step.

Through these operations, a broadcast station having a different area code, that is. a same network station of another region is selected from the same network station 27 group as the broadcast station currently being received.

When it is detected in step S57 that no receiving station exists, when it is detected in step S59 that the PI data are different from each other. or when it is judged in step S61 that the PS data totally coincide with each other, the processor judges whether or not the processes for determining the presence of the receiving station, the coincidence of the PI data with the exception of the area code, and the disagreement of the PS data have been completed for all of the AF data in the AF list (step S63). If the judgment have not been completed, the processor goes back to step S52, to repeat the procedure described above. If, on the other hand, the judgments have been completed for all of the AF data in the AF list, the processor reads-out the former AF data stored in step S51 (step S64), and supplies the read-out AF data to the PLL circuit (step S65). At the same time, the processor sets the PLL timer (step S66). After the timeout of the PLL timer (step S67), the processor proceeds to step S62, to cancel the audio muting.

By this procedure, the receiving frequency is brought back to the frequency of the originally received station. Specifically, when the regional channel selection command is generated in the regional OFF mode to perform the selection of a same network station in 22 another region, the receiving station is brought back to the original receiving station when existence of the receiving station is not detected, or when it is detected that no same network station of another region exists, by the comparison for determining the coincidence of the PI data with the exception of the area data and the comparison for determining the disagreement of the PS data.

In the case of the embodiment described above, only existence of the receiving station is detected (step S57) before the judgment of the coincidence of the PI code with the exception of the area code (step S59) and the disagreement of the PS data (step S61). However, it is also possible to arrange the apparatus that, when the existence of the receiving station is detected, the receiving signal level is retrieved from the level detection circuit 16, so that the processor proceeds to step S58 when the receiving signal level is detected to be higher than the set level.

As specifically described in the foregoing, in the third embodiment of the receiving frequency selecting method according to the present invention. the PI data of the currently selected receiving station is stored in response to a command in the regional.OFF mode, existence of a receiving station based on the AF list is detected, A 29 and a new receiving frequency is set to the frequency of the currently selected receiving station when the PI data obtained from the broadcast wave of the currently selected receiving station and the previously held PI data coincide with each other with the exception of the area code, and at the same time the PS data are different from each other.' By this operation, a same network station of another region can be positively received.

A processing procedure of a regional channel selection operation in the fourth embodiment which is executed by the processor of the controller 13 when a regional channel selection command is generated in response to a key operation by the user in the operation section 15 will now be described with reference to the flowchart of Fig. 9. It is assumed that this routine is called and executed in response to the regional channel selection command as the first command. Also in this embodiment it is further assumed that AF data obtained by the demodulation of the received broadcast wave has been already retrieved and the AF list of the same network stations-as the station currently being received has already been produced in the memory 14.

The processor first retrieves the AF data and PI data of the broadcast wave currently being received and stores those data into predetermined regions of the memory 14 (step S71). According to the AF list mentioned above, the processor reads out one of the AF data in the AF list from the memory 14 (step S72). Then the processor turns the muting circuit 18 on, to effect the audio muting (step S73), and supplies the read-out AF data to the PLL circuit (not shown) in the front-end 2 (step S74). At the same time, the processor sets a PLL timer for measuring the time period Tl required for the PLL circuit to be locked (step S75). The AF data supplied to the PLL circuit is set to the programmable frequency divider in the PLI, circuit, so that the receiving frequency changes from the current receiving frequency to another frequency of a network station within the period in which the PLL timer times-out.

After the time-out of the PLL timer (step S76), the processor judges the presence or absence of a receiving station by monitoring the station detection signal from the station detection circuit 17 (step S77). If the existence of a receiving station is detected, the processor retrieves the area code in the PI data of the receiving station (step S78). Then, the processor judges whether or not the PI data retrieved this time and the PI data held in step S1 coincide with each other with the exception of the area code (step S79). When the PI data coincide with each other, the processor further judges 31 whether or not the area code in the PI data retrieved this time differs from the area code in the PI data stored in step S71 (step S80). If the area codes are different from each other. the processor turns the muting circuit 18 off, to cancel the audio muting (step S81). Then the processor judges whether or not a return command, that is, the second command is generated by the user's operation in the operation section 15 (step S82). If the return command is not generated, the processor finishes the process of this routine.

When it is detected in step S77 that no receiving station exists, when it is detected in step S79 that the PI data are different from each other, or when it is judged in step S80 that the area codes coincide with each other, the processor judges whether or not the processes for determining the presence of the receiving stat-ion,- the coincidence of the PI data with the exception of the area code, and the disagreement of the area code have been completed for all of the AF data in the AF list (step S83). If the judgment have not been completed, the processor goes back to step S72, to repeat 32 the procedure described above. If, on the other hand, the judgments have been completed for all of the AF data in the AF list, the processor reads- out the former AF data stored in step S71 (step S84), and supplies the read-out AF data to the PLL circuit (step S85). At the same time, the processor sets the PLL timer (step S86). After the time-out of the PLL timer (step S87), the processor proceeds to step S88, to cancel the audio muting. Then the processor finishes the process of this routine.

After the muting has been canceled in step S81, if it is judged that the return command as the second command-has been generated, the processor turns the muting circuit 18 on, to effect the audio muting (step 89). Then the processor proceeds to step 84. Through these operations, when a same network station of another region is searched from the receiving station which has 1 1 33 been listened to, even if the original region can not be found out, the receiving state can be readily brought back to the state of receiving the network station of the same region in response to the generation of the return command by the key operation of the user.

Fig. 10 shows a flowchart of another processing procedure, in which steps for performing the same operations of the steps shown in Fig. 8 are denoted by the same reference numerals. In this example, after the cancellation of the muting in step S81, the processor sets a return timer of a certain constant time period T3 (step S90), and monitors the generation of the return command from the operation section 15 within the constant time period T3 in which the timer times-out (step S91). If the return command is not generated before the timeout, the processor finishes the procedure of this routine without executing any further step. If, on the other hand, the return command is generated, the processor goes back to the step S89. By this feature, reception of the return command is enabled only in the constant time period T3 after the cancellation of the audio muting.

In the case of the embodiment described above, only existence of the receiving station is detected (step S77) before the judgment of the coincidence of the PI code with the exception of the area code (step S79) and the 3i+ disagreement of the area code (step S80). However, it is also possible to arrange the apparatus that, when the existence of the receiving station is detected, the receiving signal level is retrieved from the level detection circuit 16, so that the processor proceeds to step S78 when the receiving signal level is detected to be higher than the set level.

As specifically described in the foregoing, in the receiving frequency selecting method according to the present invention, the AF data and the PI data of the currently selected receiving station are stored in response to the first command, existence of a receiving station based on the AF list is detected, and a new receiving frequency is set to the frequency of the currently selected receiving station when the PI data obtained from the broadcast wave of the currently selected receiving station and the previously held PI data coincide with each other with the exception of the area code, and at the same time the area codes in both PI data are different from each other. By this operation, a same network station of another region can be positively received.

Furthermore. if the second command is generated after the reception of a same network.station of another region, the receiving frequency is brought back to the 1 original receiving frequency given by the previously held AF data. By this feature when a same network station of another region is searched from the receiving station being listened to, even if it becomes impossible to find out the original region, the receiving condition can be brought back to the reception of the same network station of the same region in response to the generation of the return command by the key operation.

Claims

CLAIMS:-

1. A method of selecting a receiving frequency, in an RDS receiver capable of receiving an RDS broadcasting wave on which a plurality of frequency data of a same network station group and program identification data including an area code are superimposed, for changing the receiving frequency from a currently selected receiving frequency to the frequency of another same network station given by one of said plurality of frequency data, the method comprising:

a first step of holding program identification data obtained by a broadcast wave of the currently selected receiving frequency; a second step of detecting the existence of a receiving station based on the plurality of frequency data; a third step of detecting that program identification data obtained by the broadcast wave of the receiving station detected in the second step and the PI data held in the first step coincide with each other excluding the area code; and a fourth step of setting a new receiving frequency to the frequency of the receiving station selected at present if it is detected that the area code in the program identification data obtained in the third step is j not identical with the area code in the area code in the program identification data held in the first step.

2. A receiving frequency selecting method as claimed in claim 1, wherein the area code in the program identification data obtained from the broadcast wave of the receiving station is held in said third step. and the disagreement is determined in said fourth step between the area code in the program identification data obtained this time in said third step and all of the area codes held in said third step up to a previous time, and wherein operations of said second, third and fourth steps are repeated once more in the event that said command is issued again within a certain time period after the completion of the operation of said fourth step.

3. A method of selecting a receiving frequency substantially as hereinbefore described with reference to figures 3 to 5, 6, 7, 8, 9 or 10 of th accompanying drawings.

Publish d 1991 at The Patent Office, State House. 66171 High Holborn. London WC I R 41P. Further copies may be obtained from ea Sales Branch. Unit 6. Nine Mile Point Cwmfelinfach. Cross Keys, Newport. NP1 7HZ. Printed by Multiplex techniques lid. St Mary Cray. Kent.