©Copyright 2000-2007 SD Card Association
SDIO Simplified Specification Version 2.00
An SDIO aware host sends CMD5 prior to the CMD55/ACMD41 pair, and thus would receive a valid OCR in the R4 response to CMD5 and continue to initialize the card. Figure 3-2 shows the operation of an SDIO aware host operating in the SD modes and Figure 3-3 shows the same operation for a host that operates in the SPI mode.
If the I/O portion of a card has received no CMD5, the I/O section remains inactive and shall not respond to any command except CMD5. A combo card stays in the memory-only mode. If no memory is installed on the card (i.e. an I/O only card in a non-SDIO aware host) the card would not respond to any memory command. This satisfies the condition where a user uses some I/O function on the card such as Ethernet to load a music file to the memory function of that card. The card is then removed and inserted into a non-SDIO aware host. That host would not enable the I/O function (no CMD5) so would appear to the player as a memory-only card. If the host were I/O aware, it would send the CMD5 to the card and the card would respond with R4. The host reads that R4 value and knows the number of available I/O functions and about the existence of any SD memory.
After the host has initialized the I/O portion of the card, it then reads the Common Information Area (CIA) of the card (see 6.8). This is done by issuing a read command, starting with the byte at address 0x00, of I/O function 0. The CIA contains the Card Common Control Registers (CCCR) and the Function Basic Registers (FBR). Also included in the CIA are pointers to the card’s common Card Information Structure (CIS) and each individual function’s CIS. The CIS structure is defined in section 16. The CIS includes information on power, function, manufacturer and other things the host needs to determine if the I/O function(s) is appropriate to power-up. If the host determines that the card should be activated, a register in the CCCR area enables the card and each individual function. At this time, all functions of the I/O card are fully available. In addition, the host can control the power consumption and enable/disable interrupts on a function-by-function basis. This access to I/O does not interfere with memory access to the card if present.
Combo Cards can accept CMD15 with RCA=0000, as described in, but there is an exception for SD memory only cards. Memory only cards require a non-zero RCA before the host may issue CMD15. Thus, CMD15 shall be issued after CMD3 in the Standby state. In the case of ACMD41, it shall accept RCA=0x0000.
As shown in Figure 3-2 and Figure 3-3, an SDIO aware host shall send CMD5 arg=0 as part of the initialization sequence after either Power On or a CMD 52 with write to I/O Reset. Sending CMD5 arg=0 that has not been preceded by one of these two reset conditions shall not result in either the host or card entering the initialization sequence.
