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2 CRC bytes
Busy
low
Start
bit
End
bit
Start
bit
End
bit
CMD
Data
CLK
2.3.2MMC/SDModeReadSequence
PeripheralArchitecture
Figure5.MMC/SDModeWriteSequenceTimingDiagram
Table2.MMC/SDModeWriteSequence
Portionofthe
SequenceDescription
WRCMDWritecommand:A6-byteWRITE_BLOCKcommandtokenissentfromtheARMtothecard.
CMDRSPCommandresponse:Thecardsendsa6-byteresponseoftypeR1toacknowledgetheWRITE_BLOCKtothe
ARM.
DATBLKDatablock:TheARMwritesablockofdatatothecard.Thedatacontentisprecededbyonestartbitandis
followedbytwoCRCbytesandoneendbit.
CRCSTATCRCstatus:ThecardsendsaonebyteCRCstatusinformation,whichindicatestotheARMwhetherthedatahas
beenacceptedbythecardorrejectedduetoaCRCerror.TheCRCstatusinformationisprecededbyonestart
bitandisfollowedbyoneendbit.
BSYBUSYbit:TheCRCstatusinformationisfollowedbyacontinuousstreamoflowbusybitsuntilallofthedatahas
beenprogrammedintotheflashmemoryonthecard.
Figure6andTable3showthesignalactivitywhentheMMCcontrollerisintheMMC/SDmodeandis
readingdatafromamemorycard.ThesameblocklengthmustbedefinedintheMMCcontrollerandin
thememorycardbeforeinitiatingadataread.Inasuccessfulreadprotocolsequence,thefollowingsteps
occur:
•TheMMC/SDcontrollerrequestsfortheCSDcontent.
•ThecardreceivesthecommandandsendsthecontentoftheCSDregisterasitsresponse.
•Ifthedesiredblocklength,READ_BL_LENvalue,isdifferentfromthedefaultvaluedeterminedfrom
theresponse,theMMC/SDcontrollersendstheblocklengthcommand.
•Thecardreceivesthecommandandsendsresponsestothecommand.
•TheMMC/SDcontrollerrequeststhecardtochangestatefromstand-bytotransfer.
•Thecardreceivesthecommandandsendsresponsestothecommand.
•TheMMC/SDcontrollersendsareadcommandtothecard.
•Thecarddrivesresponsestothecommand.
•ThecardsendsablockofdatatotheARM.
14MultimediaCard(MMC)/SecureDigital(SD)CardControllerSPRUE30B–September2006
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