SanDisk SD Card

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Revision 2.2Chapter 4 – SD Card Protocol DescriptionSanDisk SD Card Product Manual4.2 Functional DescriptionThe host (master) controls all communication between it and the SD Card. The host sendsthe following two types of commands:• Broadcast Commands— Broadcast commands are intended for all SD cards. Some ofthese commands require a response.• Addressed (Point-to-Point) Commands— The addressed commands are sent to theaddressed SD Card and cause a response to be sent from this card.A general overview of the command flow is shown in Figure 4-7 for the Card IdentificationMode and in Figure 4-8 for the Data Transfer Mode. The commands are listed in Tables 4-15 and 4-16. The dependencies among the current SD Card, received-command andfollowing states are listed in Table 4-18. In the following sections, the various cardoperation modes will be described first. Thereafter, the restrictions for controlling the clocksignal are defined. All SD Card commands, together with corresponding responses, statetransitions, error conditions, and timings are presented in the following sections.The SanDisk SD Card has two operation modes.• Card Identification Mode— The host will be in card identification mode after resetand while it is looking for new cards on the bus. SD cards will be in this mode afterreset until the SET_RCA command (CMD3) is received.• Data Transfer Mode— SD cards will enter data-transfer mode when their RCA is firstpublished. The host will enter data-transfer mode after identifying all SD cards on thebus.Table 4-1 lists the dependencies between operation modes and card states. Each state in thecard state diagrams (Figure 4-7 and 4-8) is associated with one operation mode.Table 4-1Card States vs. Operation Modes OverviewInactiveCard StateInactiveOperation ModeIdle, Ready, IdentificationCard Identification ModeStandby, Transfer, Send data, Receive data,Programming, DisconnectData Transfer Mode4.3 Card Identification ModeIn Card Identification Mode the host resets all cards, validates operation voltage range,identifies and requests cards to publish a Relative Card Address (RCA). This operation isperformed on each card separately using its own command (CMD) line. All datacommunication in the Card Identification Mode uses the CMD line only.© 2004 SanDisk Corporation 4-4 12/08/04
Revision 2.2Chapter 4 – SD Card Protocol DescriptionSanDisk SD Card Product ManualFigure 4-7SD Memory Card State Diagram—Card Identification ModePower OnSPI OperationModeCMD0CS Asserted (0)Idle State (idle)CMD0From all statesexcept "ina"Card is busy orhost omittedvoltage rangeACMD41Inactive State (ina)CMD15No response (nonvalid command)must be an MMCStart MMCinitialization processstarting at CMD1Ready State(ready)CMD2Cards w/non-compatible voltage rangeIdentification State(ident)Card Identification ModeCMD3Card respondsw/new RCAData Transfer ModeStandby State(stby)CMD3Card respondsw/new RCAFrom all states inData TransferMode4.3.1 ResetThe GO_IDLE_STATE (CMD0) is the software-reset command that makes each SD Cardmove into an idle state regardless of the card’s current state. Cards already in an inactivestate are not affected by this command.After power-on by the host, all cards are in an idle state, including cards that were in aninactive state. 1After power-on or CMD0, all card CMD lines are in input mode, waiting for the start-bit ofthe next command. The cards are initialized with a default relative card address(RCA=0x0000) and a default driver-stage-register setting (lowest speed, highest drivingcurrent capability).4.3.2 Operating Voltage Range ValidationThe physical specification standard, defined by the SDA, requires that all SD cards can useany operating voltage between V DD -min and V DD -max to establish communication with thehost. However, during data transfer, minimum and maximum values for V DD are defined inthe Operations Condition Register (OCR) and may not cover the entire range. Card hostsare expected to read the CSD Register and select proper V DD values or reject the card.An SD Card that stores the CID and CSD data in the payload memory can communicatethis information under data-transfer V DD conditions only. In other words, if the host and1 At least 74 clock cycles are required prior to starting bus communication.© 2004 SanDisk Corporation 4-5 12/08/04
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