Specifications

Physical Layer Simplified Specification Version 4.10

4.2.3 Card Initialization and Identification Process

After the bus is activated the host starts card initialization and identification process (See Figure 4-2).

The initialization process starts with SD_SEND_OP_COND (ACMD41) by setting its operational

conditions and the HCS bit in the OCR. The HCS (Host Capacity Support) bit set to 1 indicates that the

host supports SDHC or SDXC Card. The HCS (Host Capacity Support) bit set to 0 indicates that the

host supports neither SDHC nor SDXC Card.

Receiving of CMD8 expands the ACMD41 function; HCS in the argument and CCS (Card Capacity

Status) in the response. HCS is ignored by cards, which didn't respond to CMD8. However the host

should set HCS to 0 if the card returns no response to CMD8. Standard Capacity SD Memory Card

ignores HCS. If HCS is set to 0, SDHC and SDXC Cards never return ready status (keep busy bit to 0).

The busy bit in the OCR is used by the card to inform the host whether initialization of ACMD41 is

completed. Setting the busy bit to 0 indicates that the card is still initializing. Setting the busy bit to 1

indicates completion of initialization. Card initialization shall be completed within 1 second from the first

ACMD41. The host repeatedly issues ACMD41 for at least 1 second or until the busy bit are set to 1.

The card checks the operational conditions and the HCS bit in the OCR only at the first ACMD41 with

setting voltage window in the argument. While repeating ACMD41, the host shall not issue another

command except CMD0.

If the card responds to CMD8, the response of ACMD41 includes the CCS field information. CCS is

valid when the card returns ready (the busy bit is set to 1). CCS=0 means that the card is SDSC.

CCS=1 means that the card is SDHC or SDXC.

The host performs the same initialization sequence to all of the new cards in the system. Incompatible

cards are sent into Inactive State. The host then issues the command ALL_SEND_CID (CMD2), to

each card to get its unique card identification (CID) number. Card that is unidentified (i.e. which is in

Ready State) sends its CID number as the response (on the CMD line). After the CID was sent by the

card it goes into Identification State. Thereafter, the host issues CMD3 (SEND_RELATIVE_ADDR) asks

the card to publish a new relative card address (RCA), which is shorter than CID and which is used to

address the card in the future data transfer mode. Once the RCA is received the card state changes to

the Stand-by State. At this point, if the host wants to assign another RCA number, it can ask the card to

publish a new number by sending another CMD3 command to the card. The last published RCA is the

actual RCA number of the card.

The host repeats the identification process, i.e. the cycles with CMD2 and CMD3 for each card in the

system.

Initialization of SDXC is identical to SDHC. User area capacity of SDXC card is specified by C_SIZE

and it shall be more than or equal to 32GB.

Figure 4-2 shows Card Initialization and Identification for SD I/F. In case of UHS-II mode, refer to SD-

TRAN Section of the UHS-II Addendum.

Application Notes:

The host shall set ACMD41 timeout more than 1 second to abort repeat of issuing ACMD41 when

the card does not indicate ready. The timeout count starts from the fi

rst ACMD41 which is set

voltage window in the argument.