an embodiment according to the present invention will be described in detail with reference to the accompanying drawings . the scope of the claimed invention should not be limited to the examples illustrated in the drawings and those described below . a first embodiment according to the present invention will be described referring to fig1 . fig1 is a view showing a block configuration according to the first embodiment ( 3 to 1 arbitration ) of the present invention . a ts conversion module ( 000 ) receives and digitally demodulates broadcast waves from terrestrial digital broadcasting , satellite broadcasting and catv and outputs demodulated signals as encrypted transport streams ( tss ) a ts - to - ntsc conversion module ( 100 ) receives the encrypted tss input from the ts conversion module ( 000 ) using ts / ds units ( transport stream data decoder / data descrambler units ) ( 120 ), takes out data from the tss and outputs descrambled video / audio data as video / audio signals from an av decoder ( 130 ) via a b - cas i / f bridge ( 110 ) while inquiring a b - cas card ( 200 ) about keys , etc . the b - cas i / f bridge ( 110 ) is used to bridge internal bus signals to the b - cas card ( 200 ) via b - cas access block buffers ( 111 ), a request arbiter ( 112 ) and a protocol manager ( 113 ). when a request block is held in one of the b - cas access block buffers ( 111 ), a b - cas card access request is generated . in the case that requests from plural b - cas access block buffers ( 111 ) compete , the request arbiter ( 112 ) selects a card accessible request on the basis of the order of priority according to arbitration timing output from the protocol manager ( 113 ). the order of priority should only be determined by a method , such as round - robin . the request arbiter ( 112 ) and the protocol manager ( 113 ) can be configured relatively easily using flip - flop and combinational / sequential circuits . in the case that another precedent transaction occupies the b - cas card , an access request buffered in one of the block buffers ( 111 ) is arbitrated immediately after the precedent transaction is completed and can access the b - cas card without software control . the protocol manager ( 113 ) manages the transmission of a request block to the b - cas card ( 200 ) and the reception of a response block therefrom as one transaction and outputs arbitration timing to the request arbiter ( 112 ) at the boundary of the transaction . the b - cas access block buffers ( 111 ) are used as temporary storage areas for request and response blocks . b - cas access blocks ( request and response blocks ) herein have a format described below . nad ( 1 byte ): node address pcb ( 1 byte ): protocol control byte len ( 1 byte ): payload length inf ( 0 to 254 bytes ): information parity ( 1 byte ) hence , the b - cas access block buffer ( 111 ) is required to have a size of not less than 258 bytes . a second embodiment according to the present invention will be described referring to fig2 and 3 . fig2 is a view showing a block configuration ( 3 to 1 arbitration , b - cas card × 3 ) according to this proposed embodiment . a ts conversion module ( 000 ) receives and digitally demodulates broadcast waves from terrestrial digital broadcasting , satellite broadcasting and catv and outputs demodulated signals as encrypted transport streams ( tss ) a ts - to - ntsc conversion module ( 100 ) receives the encrypted tss input from the ts conversion module ( 000 ) using ts / ds units ( transport stream data decoder / data descrambler units ) ( 120 ), takes out data from the tss and outputs descrambled video / audio data as video / audio signals from an av decoder ( 130 ) via a b - cas i / f bridge ( 110 ) while inquiring b - cas cards ( 200 ) about keys , etc . the b - cas i / f bridge ( 110 ) is used to bridge internal bus signals to the b - cas cards ( 200 ) via b - cas access block buffers ( 111 ), host - card connection tables ( 114 ), request arbiters ( 112 ) and protocol managers ( 113 ). when a request block is held in one of the b - cas access block buffers ( 111 ), a b - cas card access request is generated . in the case that requests from plural b - cas access block buffers ( 111 ) compete , the request arbiter ( 112 ) connected to the b - cas access block buffer ( 111 ) on the basis of the setting of the host - card connection tables ( 114 ) selects a card - accessible request on the basis of the order of priority according to arbitration timing output from the protocol managers ( 113 ). even in the case that another precedent transaction occupies one of the b - cas cards , an access request buffered in one of the block buffers ( 111 ) is arbitrated immediately after the precedent transaction is completed and can access the b - cas card without software control . each protocol manager ( 113 ) manages the transmission of a request block to the b - cas card ( 200 ) and the reception of a response block therefrom as one transaction and outputs arbitration timing to the request arbiter ( 112 ) at the boundary of the transaction . the b - cas access block buffers ( 111 ) are used as temporary storage areas for request and response blocks . the host - card connection tables ( 114 ) are set by a cpu via a bus target i / f ( 115 ) before request blocks are set in the b - cas access block buffers ( 111 ). fig3 shows the host - card connection table ( 114 ) according to this embodiment . the table divides data ( req ) from the block buffer ( 111 ) connected thereto into several blocks , for example , and outputs the data to one of the request arbiters ( 112 ). it is configured that the selection of one of the request arbiters ( 112 ) to which the data is output at this time is indicated using a select signal that is output from the cpu and held in a register reg and supplied to an mux ( divider ) as sel . in the above - mentioned embodiments , a method is adopted in which the block buffers , the request arbiters and the protocol managers are disposed on the side of the b - cas cards , and b - cas card / master switching is done without software intervention . an efficient b - cas card access method for performing b - cas access competition arbitration using hardware is attained . ( 1 ) a digital broadcast receiving system in which b - cas card access requests from plural digital broadcast stream data descramblers are arbitrated in b - cas access block units using hardware ( block data buffers and arbiters ). ( 2 ) a digital broadcast receiving system having request arbiters and protocol managers as arbitration hardware for the system ( 1 ). ( 3 ) a system in which plural digital broadcast stream data descramblers are connected to plural b - cas cards on the basis of the configuration of the system ( 1 ). as described above , efficient b - cas card access can be attained by performing b - cas access competition arbitration using hardware according to the embodiments . hence , the addition of digital broadcast stream data channels is made possible up to the upper limit of the frequency band of b - cas i / f . although the embodiments according to the present invention have been described above , the present invention is not limited to the above - mentioned embodiments but can be variously modified . constituent components disclosed in the aforementioned embodiments may be combined suitably to form various modifications . for example , some of all constituent components disclosed in one of the embodiments may be removed or the constituent components disclosed in different embodiments may be appropriately combined . additional advantages and modifications will readily occur to those skilled in the art . therefore , the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein . accordingly , various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents .