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DP8402AD
DP8402A/DP8403/DP8404/DP8405 32-Bit Parallel Error Detection and Correction Circuits (EDACs)
TL/F/8535
DP8402A/DP8403/DP8404/DP8405
32-Bit
Parallel
Error
Detection
and
Correction
Circuits
(EDAC’s)
PRELIMINARY
August 1989
DP8402A/DP8403/DP8404/DP8405 32-Bit Parallel
Error Detection and Correction Circuits (EDAC’s)
General Description
The DP8402A, DP8403, DP8404and DP8405 devicesare
32-bit parallel error detection and correction circuits
(EDACs)in 52-pin DP8402Aand DP8403or 48-pin DP8404
and DP8405 600-mil packages.The EDACsusea modified
Hamming codeto generatea 7-bit check word froma 32-bit
data word. This check wordis stored along withthe data
word duringthe memory write cycle. Duringthe memory
read cycle,the 39-bit words from memoryare processedby
the EDACsto determineif errors have occurredin memory.
Single-bit errorsinthe 32-bit data wordare flaggedandcor-
rected.
Single-bit errors inthe 7-bit check wordare flagged, andthe
CPU sendsthe EDAC throughthe correction cycle even
thoughthe 32-bit data wordisnotin error.The correction
cyclewill simply pass alongthe original 32-bit data wordin
this caseand produce error syndromebitsto pinpointthe
error-generating location.
Doublebit errorsare flaggedbutnot corrected. Theseer-
rors may occurinanytwobitsofthe 39-bit word from mem-
ory (two errorsinthe 32-bit data word,two errorsinthe 7-bit
check word,or one errorin each word). The gross-error
conditionofall lowsorall highs frommemorywillbe detect-
ed. Otherwise, errorsin threeor morebitsofthe 39-bitword
are beyondthe capabilitiesof these devicesto detect.
Read-modify-write (byte-control) operations canbe per-
formed withthe DP8402Aand DP8403 EDACsby usingout-
put latch enable, LEDBO, andthe individual OEB0 thru
OEB3 byte control pins.
Diagnosticsare performedonthe EDACsby controls and
internal pathsthat allowthe userto readthe contentsoftheandCB input latches. Thesewill determineifthe failure
occurredin memoryorinthe EDAC.
Features Detects and corrects single-bit errors Detects and flags double-bit errors Built-in diagnostic capability Fast writeand read cycle processing times Byte-write capability... DP8402Aand DP8403 Fullypinand function compatible withTI’s
SN74ALS632A thru SN74ALS635 series
System Environment
TL/F/8535–1
TRI-STATEÉ isaregistered trademarkof National SemiconductorCorp.
C1995National SemiconductorCorporation RRD-B30M105/PrintedinU.S.A.
