SanDisk SD Card

Revision 2.2Chapter 3 – SD Card Interface DescriptionSD Card Product Manual3.3 SPI Bus TopologyThe SD Card SPI Interface is compatible with SPI hosts available on the market. Similar toany other SPI device, the SD Card SPI channel consists of the following four signals:• CS—Host-to-card Chip Select signal• CLK—Host-to-card Clock signal• DataIn—Host-to-card Data signal• DataOut—Card-to-host Data signalAnother SPI common characteristic implemented in the SD Card are byte transfers. Alldata tokens are multiples of 8-bit bytes and always byte-aligned to the CS signal. The SPIstandard defines the physical link only and not the complete data transfer protocol. In SPIbus mode, the SD Card uses a subset of the SD Card protocol and command set.The SD Card identification and addressing algorithms are replaced by the hardware CSsignal. A card (slave) is selected for every command by asserting the CS signal (activelow). Refer to Figure 3-2.The CS signal must be continuously active for the duration of the SPI transaction(command, response and data). The only exception is card-programming time. At this timethe host can de-assert the CS signal without affecting the programming process.The bi-directional CMD and DAT lines are replaced by unidirectional dataIn and dataOutsignals. This eliminates the ability to execute commands while data is being read or writtenwhich prevents sequential multi read/write operations. The Stop Transmission commandcan be sent during data read. In the multi block write operation a Stop Transmission tokenis sent as the first byte of the data block.Figure 3-4SD Card Bus SystemPower SupplySPI Bus MasterCSCSSPI Bus (CLK, DataIn, DataOut)SPI CardSPI Card© 2004 SanDisk Corporation 3-5 12/08/04