Abstract:
An address check system which comprises receiving stations each receiving address information and control information transmitted by a transmitting station and take the control information in when the address coincides with the own address and further has a means for detecting changes in its own address.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to an address check system and more particularly to an address check system in a system such as a pay-TV system for controlling a plurality of receiving stations by a single or a few transmitting stations, and so improved as to prevent that each receiving station gets out of the control by the transmitting station due to change of the address of the receiving station. 
     2. Description of the Prior Art 
     The system for controlling the functions of a plurality of receiving stations by a single or a few transmitting stations in the wireless manner or in a wired signal transmitting manner has generally been so arranged that different user numbers (addresses) are previously allotted to respective stations. The transmitting station sends the addresses and control information, and each receiving station then acts upon the control information only when its own address is called otherwise it ignores the control information. 
     In such a system, however, if the address of a receiving station has changed due to the disorder of the apparatus thereof or due to the unexpected operation of the apparatus with the intention or negligence of the subscriber, the receiving station ceases to function under the control by the transmitting station. However, no address checking method capable of preventing such an undesirable problem has yet conventionally been adopted. Therefore, when the abovementioned problem occurs, it has been impossible to prevent the subscriber from tapping. It is a serious problem which cannot be ignored in operating such a system. 
     OBJECT OF THE INVENTION 
     It is therefore an object of the present invention to improve the security of the system operation by providing each receiving station with a detecting means for detecting a change of its own address and interrupting the function of the receiving station in response to the detected change. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a block diagram illustrating an embodiment according to the present invention; and 
     FIG. 2 shows a circuit diagram illustrating an arrangement of the part of the address part and the address check part shown in FIG. 1. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will now be described in detail referring to the preferred embodiment illustrated in the drawings. 
     FIG. 1 shows an embodiment where the address check system according to the present invention is adopted in each receiving station of the above-described system like a pay-TV system. 
     In the same drawing, the reference numeral 1 designates an address part of the receiving station, 2 an address check part, 3 an incoming information processing part and 4 a functional part of the receiving station. 
     The user address for the receiving station is allotted to the address part 1. The incoming information processing stage 3 receives an information signal I which comprises an address information signal and a control information signal and provides the address stage 1 with a control signal C to pick up the address data therefrom. This stage 3 thereby compares the address information with the address data and transmits the control information to the operating stage 4 in response to the result of the comparison. 
     The address check stage 2 checks in a predetermined manner if its own address allotted to the address stage 1 is right or not and then outputs an address check signal to the functional stage 4 when any error is found in its own address. 
     The functional stage 4 is supplied with the control information and the address check signal to thereby perform predetermined operations. This stage, however, performs the predetermined operations in response to the control information only when the address check signal is not generated, i.e. if address match occurs, whereas it stops the operations when the address check signal is generated. 
     FIG. 2 shows the arrangement of the address stage 1 and the address check stage 2. In the same drawing, the reference numeral 5 denotes a shift register circuit, wherein FF 1  -FF n  are flip-flop circuits, AP 1  -AP n  are n address setting pins each connected to a parallel-load terminal of each of the flip-flop circuits FF 1  -FF n , P is a parity setting pin, INV 1  -INV 3  are inverters and NOR is a NOR gate. 
     The shift register circuit 5, when the control signal from the incoming information processing part 3 lowers, outputs an address data allotted to each of the flip-flop circuits FF 1  -FF n  synchronizing it with the clock signal CL and supplies the incoming information processing part 3 with it. 
     The user address is set by properly providing the respective address setting pins AP 1  -AP n  with high-level (or low-level) address setting signals. In this case, any change of its own address comprising an odd number of bits can be detected by setting a high-level (or low-level) parity signal to the parity setting pin P so that the number of the address setting pins for setting the high level signal to is odd (or even). 
     To this end, the address setting signal and the parity signal are applied to the address check stage 2. The address check stage 2 comprises a plurality of exclusive &#34;or&#34; circuits EX 1  -EX n , for example, to perform the parity check. The address check signal detected by the address check stage 2 as the result of the parity check is sent to the functional part 4. 
     Although the above-mentioned arrangement utilizes detecting methods such as parity check, by adding surplus bits to the address bits, the capacity of detecting changes of the address data can be further improved by dividing each series of the address bits of the address setting signal into several groups and detecting changes of the address data on each group. 
     Further, various methods for detecting change of the local address may be used in addition to the parity check. For example, one would be to record the number of the bits to be set at a high (or low) level among the address bits and store a representation thereof in the surplus bits using binary digits. 
     As described above, according to the present invention where the receiving stations have such an address check function, it is possible to easily prevent each receiving station from passing out of the control of the system and not to continue its function when its address has been changed. 
     Further, when the parity setting pin P is placed among the address setting pins as in the above-mentioned embodiment, the secrecy of the address increases from the viewpoint of the outward appearance.