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©Copyright 2000-2007 SD Card Association
SDIO Simplified Specification Version 2.00
4
3. SDIO
Card
Initialization
3.1
Differences in I/O card Initialization
A requirement for the SDIO specification is that an SDIO card shall not cause non-I/O aware hosts to fail when
inserted. In order to prevent operation of I/O functions in non-I/O aware hosts, a change to the SD card
identification mode flowchart is needed. A new command (IO_SEND_OP_COND, CMD5) is added to replace
the ACMD41 for SDIO initialization by I/O aware hosts (see 3.2).
After reset or power-up, all I/O functions on the card are disabled and the I/O portion of the card shall not
execute any operation except CMD5 or CMD0 with CS=low. If there is SD memory installed on the card (also
called a combo card), that memory shall respond normally to all normal mandatory memory commands.
An I/O only card shall not respond to the ACMD41 and thus appear initially as an MMC card (See appendix B.1
for information on the MMC specification). The I/O only card shall also not respond to the CMD1 used to initialize
the MMC cards and appear as a non-responsive card. The host then gives up and disables this card. Thus, the
non-aware host receives no response from an I/O only card and force it to the inactive state. The operation of an
I/O card with a non-I/O aware host is shown in Figure 3-1 Note that the solid lines are the actual paths taken
while the dashed lines are not executed.
Figure 3-1 SDIO response to non-I/O aware initialization
Idle State
CMD0 + CS
asserted (0)
SPI Mode Idle
State
Inactive State
SPI
SD
Reset
SDIO card is
Rejected
No
Response
Response
No
Response
Normal SPI
memory operation
ACMD41
(arg = 00)
ACMD41
arg = working
voltage
Response
Normal SD
memory operation
CMD1 or
ACMD41
Busy
CMD1
Card is MMC
Response
No
Response
SDIO card is
Rejected
Invalid
Cmd
CMD58
(optional)
Busy
Invalid
Cmd
CMD0