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Secure Digital (SD) Card Protocol Description
4.3.2. Operating Voltage Range Validation
The SD Physical Specification standard requires that all SD Cards will be able to establish communication with the
host using any operating voltage between V
-min and V
-max. However, during data transfer, minimum and
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maximum values for V
are defined in the operation condition register (OCR) and may not cover the whole range.
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SD Card hosts are expected to read the card's OCR register and select proper V
values or reject the card.
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SD Cards that store the CID and CSD data in the payload memory can communicate this information only under
data-transfer V
conditions. This means if host and card have non-compatible V
ranges, the card will not be able
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to complete the identification cycle, nor to send CSD data.
SD_SEND_OP_COND (ACMD41) is designed to provide SD Card hosts with a mechanism to identify and reject
cards that do not match the host's desired V
range. This is accomplished by the host sending the required V
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voltage window as the operand of this command. SD Cards that cannot perform data transfer in the specified range
must discard themselves from further bus operations and go into Inactive State. Note that ACMD41 is an
application-specific command. Therefore, APP_CMD (CMD55) will always precede ACMD41. The RCA to be
used for CMD55 in idle_state will be the card's default RCA = 0x0000.
The MultiMediaCard will not respond to ACMD41 (actually it will not respond to APP_CMD—CMD55, that
precedes it). The MultiMediaCard will be initialized as per the MultiMediaCard spec, using SEND_OP_COND
command (CMD1 of MultiMediaCard). The host should ignore an ILLEGAL_COMMAND status in the
MultiMediaCard response to CMD3, since it is a residue of ACMD41 which is invalid in the MultiMediaCard
(CMD0, 1, 2 do not clear the status register). Actually, ACMD41 and CMD1 will be used by the host to distinguish
between MultiMediaCard and SD Cards in a system.
By omitting the voltage range in the command, the host can query each card and determine if there are any non
compatibilities before sending out-of-range cards into the Inactive State. This query should be used if the host can
select a common voltage range or wants to notify the application of non-usable cards in the stack.
The busy bit in the ACMD41 response can be used by a card to tell the host that it is still working on its power-
up/reset procedure (e.g., downloading the register information from memory field) and is not ready yet for
communication. In this case the host must repeat ACMD41 until the busy bit is cleared.
During the initialization procedure, the host is not allowed to change the OCR values. Changes in the OCR content
will be ignored by the SD Card. If there is a real change in the operating conditions, the host must reset the card
stack (using CMD0) and begin the initialization procedure once more. However, for accessing the cards already in
Inactive State, a hard reset must be done by switching the power supply off and on.
GO_INACTIVE_STATE (CMD15) can also be used to send an addressed SD Card into the Inactive State. This
command is used when the host explicitly wants to deactivate a card (e.g., host is changing V
into a range which
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is known to be not supported by this card).
4.3.3. Card Identification Process
The host starts the card identification process with the identification clock rate f
(see Section 3.4.4). In SD Card
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the CMD line output drives are push-pull drivers.
SanDisk Secure Digital (SD) Card Product Manual, Rev. 1.9 © 2003 SANDISK CORPORATION
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