Operating Voltage Range Validation - ST STM32L4x6 Reference Manual

SD/SDIO/MMC card host interface (SDMMC)
41.4.3

Operating voltage range validation

All cards can communicate with the SDMMC card host using any operating voltage within
the specification range. The supported minimum and maximum V
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
conditions. When the SDMMC card host module and the card have incompatible V
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
by the SDMMC card host. The SDMMC card host sends the required V
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 SDMMC
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 SDMMC card host is able
to select a common voltage range or when the user requires notification that cards are not
usable.
41.4.4 Card identification process
The card identification process differs for MultiMediaCards and SD cards. For
MultiMediaCard cards, the identification process starts at clock rate F
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 SDMMC 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 SDMMC 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
SDMMC card host and enters the Identification state.
7. The SDMMC 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
addresses the card. The assigned card changes to the Standby state, it does not react
to further identification cycles, and its output switches from open-drain to push-pull.
8. The SDMMC card host repeats steps 5 through 7 until it receives a timeout condition.
For the SD card, the identification process starts at clock rate F
line output drives are push-pull drivers instead of open-drain. The registration process is
accomplished as follows:
1410/1693 DocID024597 Rev 3
RM0351
values are defined in
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range desired
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voltage window
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. The SDMMC_CMD
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