SanDisk SD Card

Revision 2.2Chapter 3 – SD Card Interface DescriptionSD Card Product ManualDuring the initialization process, commands are sent to each card individually, allowing theapplication to detect the cards and assign logical addresses to the physical slots. Data isalways sent to each card individually. However, to simplify the handling of the card stack,after initialization, all commands may be sent concurrently to all cards. Addressinginformation is provided in the command packet.The SD bus allows dynamic configuration of the number of data lines. After power-up, bydefault, the SD Card will use only DAT0 for data transfer. After initialization, the host canchange the bus width (number of active data lines). This feature allows and easy trade offbetween hardware cost and system performance.Figure 3-3Bus Circuitry DiagramR DATR CMDR WPWrite ProtectCMDDAT0-3SDMemoryC 1 C 2 C 3CardHost 1 2 3 4 5 6 7 89VssCLKSD MemoryCardR DAT and R CMD are pull-up resistors protecting the CMD and DAT line against bus floatingwhen no card is inserted or all card drivers are in a hi-impedance mode.R WP is used for the Write Protect Switch. See Section 5.4.2 for the component values andconditions.3.2.1 Hot Insertion and RemovalHot insertion and removal are allowed; inserting or removing the SD Card to or from thebus will not damage the card. This also applies when the power is up.• The inserted card will be properly reset when CLK carries a clock frequency (f pp ).• Data transfer failures induced by removal/insertion should be detected by the busmaster using the CRC codes that suffix every bus transaction.3.2.2 Power ProtectionCards can be inserted or removed to and from the bus without damage, however if one ofthe supply pins (V DD or V SS ) is not connected properly, the current is drawn through a dataline to supply the card.Data transfer operations are protected by CRC codes; therefore, the SD bus master candetect any bit changes induced by card insertion and removal. Also, the inserted card mustbe properly reset when CLK carries a clock frequency f PP .If the hot insertion feature is implemented in the host, the host must withstand a shortcutbetween V DD and V SS without damage.© 2004 SanDisk Corporation 3-4 12/08/04