SanDisk SD Card

Revision 2.2Chapter 4 – SD Card Protocol DescriptionSanDisk SD Card Product Manual4.7.2 Read, Write and Erase Time-out ConditionsThe period after which a time-out condition for read/write/erase operations occurs is (cardindependent) either 100 times longer than the typical access times for the operations givenin Table 4-6 or 100 ms (whichever is lower). The times after which a time-out condition forWrite/Erase operations occur are (card independent) either 100 times longer than thetypical program times for these operations given below or 250 ms (whichever is lower). Acard will complete the command within this time period, or give up and return an errormessage. If the host does not get any response with the given time-out it should assume thecard is not going to respond anymore and try to recover (e.g., reset the card, power cycle,reject). The typical access and program times are defined as shown in Table 4-6.Table 4-12OperationReadWriteEraseTypical Access and Program TimeDefinitionThe read access time is defined as the sum of the two times given by the CSDparameters TAAC and NSAC. These card parameters define the typical delaybetween the end bit of the read command and the start bit of the data block.This number is card-dependent and should be used by the host to calculatethroughput and the maximal frequency for stream read.The R2W_FACTOR field in the CSD is used to calculate the typical blockprogram time obtained by multiplying the read access time by this factor. Itapplies to all write/erase commands (e.g., SET (CLEAR)_WRITE_PROTECT,PROGRAM_CSD (CID) and the block write commands).The duration of an erase command will be (order of magnitude) the number ofsectors to be erased multiplied by the block write delay.4.8 CommandsThe following sections provide information about commands.4.8.1 Command TypesThere are four kinds of commands defined to control the SD Card bus as shown in Table 4-13.Table 4-13Command DefinitionCommand Abbreviation DefinitionBroadcast bc Applicable only if all the CMD lines areconnected together in the host. If theyare separate, each card will accept itseparately in turn.Broadcast w/Response bcr Response from all cards simultaneously.Because there is not an open-drainmode in the SD Card, this command isused only if all the CMD lines areseparate. The command will be acceptedand responded to by every cardseparately.Addressed point-to-point ac No data transfer on DAT.Addressed point-to-point data transfer adtc Data transfer on DAT.The command transmission always starts with the most significant bit (MSB).© 2004 SanDisk Corporation 4-30 12/08/04