RM0390 Rev 4 991/1328
RM0390 Secure digital input/output interface (SDIO)
1031
29.4.2 Card reset
The GO_IDLE_STATE command (CMD0) is the software reset command and it puts the
MultiMediaCard and SD memory in the Idle state. The IO_RW_DIRECT command (CMD52)
resets the SD I/O card. After power-up or CMD0, all cards output bus drivers are in the high-
impedance state and the cards are initialized with a default relative card address
(RCA=0x0001) and with a default driver stage register setting (lowest speed, highest driving
current capability).
29.4.3 Operating voltage range validation
All cards can communicate with the SDIO card host using any operating voltage within the
specification range. The supported minimum and maximum V
DD
values are defined in the
operation conditions register (OCR) on the card.
Cards that store the card identification number (CID) and card specific data (CSD) in the
payload memory are able to communicate this information only under data-transfer V
DD
conditions. When the SDIO card host module and the card have incompatible V
DD
ranges,
the card is not able to complete the identification cycle and cannot send CSD data. For this
purpose, the special commands, SEND_OP_COND (CMD1), SD_APP_OP_COND
(ACMD41 for SD Memory), and IO_SEND_OP_COND (CMD5 for SD I/O), are designed to
provide a mechanism to identify and reject cards that do not match the V
DD
range desired
by the SDIO card host. The SDIO card host sends the required V
DD
voltage window as the
operand of these commands. Cards that cannot perform data transfer in the specified range
disconnect from the bus and go to the inactive state.
By using these commands without including the voltage range as the operand, the SDIO
card host can query each card and determine the common voltage range before placing out-
of-range cards in the inactive state. This query is used when the SDIO card host is able to
select a common voltage range or when the user requires notification that cards are not
usable.
29.4.4 Card identification process
The card identification process differs for MultiMediaCards and SD cards. For
MultiMediaCard cards, the identification process starts at clock rate F
od
. The SDIO_CMD
line output drivers are open-drain and allow parallel card operation during this process. The
registration process is accomplished as follows:
1. The bus is activated.
2. The SDIO card host broadcasts SEND_OP_COND (CMD1) to receive operation
conditions.
3. The response is the wired AND operation of the operation condition registers from all
cards.
4. Incompatible cards are placed in the inactive state.
5. The SDIO card host broadcasts ALL_SEND_CID (CMD2) to all active cards.
6. The active cards simultaneously send their CID numbers serially. Cards with outgoing
CID bits that do not match the bits on the command line stop transmitting and must wait
for the next identification cycle. One card successfully transmits a full CID to the SDIO
card host and enters the Identification state.
7. The SDIO card host issues SET_RELATIVE_ADDR (CMD3) to that card. This new
address is called the relative card address (RCA); it is shorter than the CID and
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