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DP8402A Datasheet(PDF) 5 Page - National Semiconductor (TI) |
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DP8402A Datasheet(HTML) 5 Page - National Semiconductor (TI) |
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5 / 18 page  Memory Read Cycle (Error Detection Correction Details) (Continued) 1) Single data bit errors cause 3 or 5 bits in the syndrome word to go low The columns of the check bit syndrome matrix (TABLE II) are the syndrome words for all single bit data errors in the 32 bit word (also see TABLE V) The data bit in error corresponds to the column in the check bit syndrome matrix that matches the syndrome word For instance the syndrome word indicating that data bit 31 is in error would be (CB6-CB0) e ‘‘0001010’’ see the column for data bit 31 in TABLE II or see TABLE V During mode 3 (S0 e S1 e 1) the syndrome word is decoded during single data bit errors and used to invert the bit in error thus correcting the data word The correct- ed word is made available on the data IO port (DB0 thru DB31) the check word IO port (CB0 thru CB6) presents the 7-bit syndrome error code This syndrome error code can be used to locate the bad memory chip 2) A single check bit error will cause that particular check bit to go low in the syndrome word 3) A double bit error will cause an even number of bits in the syndrome word to go low The syndrome word will then be the EXCLUSIVE NOR of the two individual syndrome words corresponding to the 2 bits in error The two-bit error is not correctable since the parity tree can only identify single bit errors If any of the bits in the syndrome word are low the ‘‘ERR’’ flag goes low The ‘‘MERR’’ (dual error) flag goes low during any double bit error conditions (See Table III) Three or more simultaneous bit errors can cause the EDAC to believe that no error a correctable error or an uncorrect- able error has occurred and will produce erroneous results in all three cases It should be noted that the gross-error conditions of all lows and all highs will be detected TABLE V Syndrome Decoding Syndrome Bits Error 6 5 43210 L L LLLLL unc L L LLLL H 2-bit L L L L L H L 2-bit LL L L L HH unc L L L L H L L 2-bit L L L LHLH unc LL L L HH L unc L L L L H H H 2-bit L L L H L L L 2-bit L LLHL LH unc L LLHLHL DB31 L LLHLH H 2-bit L LLH HL L unc L L L H H L H 2-bit L L L H H H L 2-bit LL L HHHH DB30 L L H LLLL 2-bit LLH L L L H unc L L H L L H L DB29 L L H L L H H 2-bit L L HLHL L DB28 L L HLHLH 2-bit L L H L H H L 2-bit L L H L H H H DB27 LLHH L L L DB26 LLHH L L H 2-bit L L H HLHL 2-bit L L H H L H H DB25 LLHHH L L 2-bit LLHHH L H DB24 LLHHHH L unc LLHHHHH 2-bit CB X e error in check bit X DB Y e error in data bit Y 2-bit e double-bit error unc e uncorrectable multibit error Syndrome Bits Error 6 543210 L H L L L L L 2-bit L H LLLL H unc L H L L LHL DB7 L H L L L H H 2-bit L H L L H L L DB6 L H L L H L H 2-bit L H L L H H L 2-bit LH L L HHH DB5 L HLHL L L DB4 L H L H L L H 2-bit L H L H L H L 2-bit L HLHLH H DB3 L H L H H L L 2-bit L HLH HLH DB2 L HLH H H L unc L H L H H H H 2-bit LHH L L L L DB0 L H H L L L H 2-bit L H H L L H L 2-bit LHH L L HH unc L H H L H L L 2-bit LHH L H L H DB1 LHH L H H L unc L H H L H H H 2-bit LHHH L L L 2-bit LHHH L L H unc LHHH L H L unc LHHH L H H 2-bit LHHHH L L unc LHHHH L H 2-bit LHHHHH L 2-bit LHHHHHH CB6 Syndrome Bits Error 654 3 2 1 0 H L L L L L L 2-bit H L LLLL H unc H L L L LHL unc H L L L L H H 2-bit H L L L H L L unc H L L L H L H 2-bit H L L L H H L 2-bit HL L L HHH unc H LLHL L L unc H L L H L L H 2-bit H L L H L H L 2-bit H L L H L H H DB15 H L L H H L L 2-bit H LLH HLH unc H L L H H H L DB14 H L L H H H H 2-bit HLH L L L L unc H L H L L L H 2-bit H L H L L H L 2-bit H L H L L H H DB13 H L H L H L L 2-bit H L H L H L H DB12 H L H L H H L DB11 H L H L H H H 2-bit HLHH L L L 2-bit HLHH L L H DB10 HLHH L H L DB9 HLHH L H H 2-bit HLHHH L L DB8 HLHHH L H 2-bit HLHHHH L 2-bit HLHHHHH CB5 Syndrome Bits Error 6543210 H H LLLLL unc H H LLLL H 2-bit H H L L L H L 2-bit H H L L L H H DB23 H H L L H L L 2-bit H H L LHLH DB22 H H L L H H L DB21 H H L L H H H 2-bit H H L H L L L 2-bit H HLHL LH DB20 H HLHLHL DB19 H HLHLH H 2-bit H H L H H L L DB18 H H L H H L H 2-bit H H L H H H L 2-bit HH L HHHH CB4 H H H LLLL 2-bit H H H L L L H DB16 HHH L L H L unc H H H L L H H 2-bit H H HLHL L DB17 H H HLHLH 2-bit H H H L H H L 2-bit HHH L HHH CB3 HHHH L L L unc HHHH L L H 2-bit H H H HLHL 2-bit HHHH L H H CB2 HHHHH L L 2-bit HHHHH L H CB1 HHHHHH L CB0 HHHHHHH none 5 |
Similar Part No. - DP8402A |
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Similar Description - DP8402A |
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