[ 0041 ] fig4 a shows an embodiment of a hardware structure for accessing dvd data according to the invention . in fig4 a , an analog signal read from the disk 410 by a reading head 411 is converted into a digital efm data 413 by an analog signal processor 412 . the efm data is demodulated by an efmplus demodulator 414 into a row data 415 in a unit of bytes . the row data 415 is stored into a row buffer 418 via a row data interface and first inner - code decoder 416 . when the data stored in the row buffer 418 can be assembled into a set of inner - code parity , an inner - code parity decoding operation is performed on the set of data by the row data interface and first inner - code decoder 416 . a set of inner - code data is obtained by this decoding step . the set of inner - code decoded data is stored into the memory 421 . when the set of inner - code decoded data is stored into the memory 421 , if the set of inner - code decoded data is the data required for generating an error detection code , the set of inner - code decoding data is also sent to the edc generator 417 . the error detection code for this data sector is thus generated . each time when the data of the whole data sector is stored into the memory 421 , the error detection code generated by the error detection code generator 417 is also stored into the memory 421 to be used by rspc decoder 426 . when the data stored in the memory 421 can be assembled as a complete data block , the rspc decoder 426 reads the error detection codes of the 16 data sectors , which are processed by the row data interface and first inner - code decoder 416 from the memory 421 under the control of the memory controller 420 . by the error detection correction ( edc ) processor 424 , these error detection codes are stored into the edc file 422 . the rspc decoder 426 then reads any of the outer - code parity data and performs outer - code parity decoding . when an error occurs in the outer - code parity decoding process , the data stored in the memory 421 is updated . in addition , incorporating the results of error correction disclosed in u . s . patent application ser . no . 08 / 823423 , which is later issued as u . s . pat . no . 6 , 003 , 151 and assigned to the same applicant , the error detection codes of the data sector corresponding to the edc file 422 is corrected . after the rspc decoder 426 decodes decoding all the outer - code parity , the host interface 428 inspects whether the error detection codes in the error detection code file 422 corresponding to the 16 data sectors are correct . if the error detection codes are correct , the data stored in the memory 421 is sent to the host 430 . referring to fig4 b , a flow chart of a method to access dvd data is illustrated . the method is introduced with the reference of both fig4 a and fig4 b as follows . after being read , the efm data is demodulated into row data 415 by the efmplus demodulator 414 is step s 470 . in step s 472 , the row data interface 416 writes the row data 415 into the row data buffer 418 . in step s 474 , the row data is read from the row data buffer 418 . after performing an inner - code parity decoded in the first inner - code decoder 416 , an inner code decoding data is obtained . in step s 476 , after obtaining the inner - code decoded data , the error detection code is calculated by the error detection code generator 417 . the data are then stored into the memory 421 . in step s 478 , the data stored in the memory 421 is then read , followed by outer - code parity decoding by the rspc decoder 426 , a correction is performed on the data in the memory 421 and the error detection codes in the error detection code file 422 . in step s 480 , after correction , the corrected data is sent to the host 430 . the amount of data access for a memory in an ecc block is calculated as follows . in step s 476 , the data written into the memory comprises 38038 bytes plus 16 × 4 bytes ( each of the error detection code has 4 bytes ). totally , the length of the data written into the memory is 38028 + 64 = 38092 bytes . in step s 478 , the access data required to be read outer - code parity decoding is 172 × 208 = 35776 bytes . in step s 480 , the data required to be accessed for sending data to the host is 16 × 2048 = 32768 bytes . thus , for each ecc block , the data required to be accessed has a length of 38092 + 35776 + 32768 = 106636 bytes . compared to the conventional structure , only 60 % of the data flow is used . therefore , for a 16 speed dvd with a conventional structure , a sdram of 120 mhz is required , while only a sdram of 72 mhz is used in the structure provided by the invention . it is worth noting the size of the row data buffer 418 and the error detection code file 422 . since only 16 sets of error detection codes are stored in the error detection code file 422 , only 64 bytes are required . to ensure that the row data can be transferred continuously during the inner - code parity decoding procedure , a space for two inner - code parity codes of 364 bytes is required . since these two regions are not large , it can be achieved by building an sram into the dvd integrated circuit . [ 0054 ] fig5 shows another flow chart of the method for accessing dvd data . in step s 500 , the flow starts only while a read command is received . the read signal includes data such as the id of the data sector to be read initially . whether a repeating reading flag for data reading due to an error in the error detection code is also included . in step s 505 , according to read signal , the data sector to be read is found . in the embodiment , whether the currently read data sector is the required one is determined by monitoring the row data from the row data interface . when the id of the row data is identical to the id of the data sector to be read , the read data sector is determined as the required one . at the step s 510 , if the read data sector is under a re - reading state , and the error detection codes of the data sector read current are correct , being controlled , the currently read data sector is skipped at the step s 520 . if the currently read data sector is not under a re - reading state , or the error detection codes are not correct , the data sector is read at the step s 515 , and a routine process is performed on the current read data sector . the so - called “ routine process ” is the procedure to write data and to send the data to the host . in step s 520 , the currently read data sector is skipped , or after the step s 515 that the routine process is performed , step s 525 determines whether the read data sector is the last sector of the ecc block . that is , whether the flag of the id representing the read data sector is 15 ( each ecc block contains 16 data sectors of id 0 - 15 ). if it is not the last sector , the flag is added with 1 in step s 535 . a data sector subsequent to this data sector is processed . on the contrary , at the step s 530 , if this is the last sector of the ecc block , it indicates that the subsequent data to be read is the data of another ecc block . thus , in step s 535 , the flag is set as 0 to access the data of the next ecc block . while performing a rspc decoding step , to avoid correcting the data that is correct in a previous rspc decoding step , if any error occurs after each outer - code parity decoding , and the error occurs at the data sector as shown in fig2 a , the result is treated as unreliable . the decoding result has to be abandoned without performing any correction . as a summary , the invention comprises at least the advantages that the required data amount for accessing a memory is reduced . therefore , the data accessing speed for dvd can be performed under a lower operation speed . in addition , the method to access the data is modified into a method that only decoding the part with errors , so that the efficiency for data access is enhanced . other embodiments of the invention will appear to those skilled in the art from consideration of the specification and practice of the invention disclosed herein . it is intended that the specification and examples to be considered as exemplary only , with a true scope and spirit of the invention being indicated by the following claims .