Chapter 4 – SD Card Protocol Description
Revision 2.2 SanDisk SD Card Product Manual
© 2004 SanDisk Corporation 4-30 12/08/04
4.7.2 Read, Write and Erase Time-out Conditions
The period after which a time-out condition for read/write/erase operations occurs is (card
independent) either 100 times longer than the typical access times for the operations given
in Table 4-6 or 100 ms (whichever is lower). The times after which a time-out condition for
Write/Erase operations occur are (card independent) either 100 times longer than the
typical program times for these operations given below or 250 ms (whichever is lower). A
card will complete the command within this time period, or give up and return an error
message. If the host does not get any response with the given time-out it should assume the
card 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 4-12 Typical Access and Program Time
Operation Definition
Read The read access time is defined as the sum of the two times given by the CSD
parameters TAAC and NSAC. These card parameters define the typical delay
between 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 calculate
throughput and the maximal frequency for stream read.
Write The R2W_FACTOR field in the CSD is used to calculate the typical block
program time obtained by multiplying the read access time by this factor. It
applies to all write/erase commands (e.g., SET (CLEAR)_WRITE_PROTECT,
PROGRAM_CSD (CID) and the block write commands).
Erase The duration of an erase command will be (order of magnitude) the number of
sectors to be erased multiplied by the block write delay.
4.8 Commands
The following sections provide information about commands.
4.8.1 Command Types
There are four kinds of commands defined to control the SD Card bus as shown in Table 4-
13.
Table 4-13 Command Definition
Command Abbreviation Definition
Broadcast bc Applicable only if all the CMD lines are
connected together in the host. If they
are separate, each card will accept it
separately in turn.
Broadcast w/Response bcr Response from all cards simultaneously.
Because there is not an open-drain
mode in the SD Card, this command is
used only if all the CMD lines are
separate. The command will be accepted
and responded to by every card
separately.
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).
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