Introduction to the SD Card
SanDisk Secure Digital (SD) Card Product Manual, Rev. 1.9 © 2003 SANDISK CORPORATION
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1.5.9.6. Read and Write Operations
The SD Card supports two read/write modes as shown in Figure 1-3.
Single Block Mode
Memory
Sectors
Memory
Sectors
Memory
Sectors
Memory
Sectors
Memory
Sectors
Memory
Sectors
Memory
Sectors
Misalignment Error
Start
Address
(Read)
Start
Address
(Write)
Start
Address
(Read/Write)
Memory
Sectors
Memory
Sectors
Memory
Sectors
Memory
Sectors
Memory
Sectors
Memory
Sectors
Memory
Sectors
Multiple Block Mode
Write
Read
Start
Address
Stop
Start
Stop
Figure 1-3. Data Transfer Formats
Single Block Mode
In this mode the host reads or writes one data block in a pre-specified length. The data block transmission is
protected with 16-bit CRC that is generated by the sending unit and checked by the receiving unit.
The block length for read operations is limited by the device sector size (512 bytes) but can be as small as a single
byte. Misalignment is not allowed. Every data block must be contained in a single physical sector. The block length
for write operations must be identical to the sector size and the start address aligned to a sector boundary.
Multiple Block Mode
This mode is similar to the single block mode, but the host can read/write multiple data blocks (all have the same
length) which will be stored or retrieved from contiguous memory addresses starting at the address specified in the
command. The operation is terminated with a stop transmission command.
Misalignment and block length restrictions apply to multiple blocks as well and are identical to the single block
read/write operations.
1.5.9.7. Data Transfer Rate
The SD Card can be operated using either a single data line (DAT0) or four data lines (DAT0-DAT3) for data
transfer. The maximum data transfer rate for a single data line is 25 Mbit per second and for four data lines it is 100
Mbit (12 MB) per second.
