RM0368 Datasheet, PDF (628/841 Pages) STMicroelectronics – This Reference manual targets application developers

Secure digital input/output interface (SDIO)
RM0368
at the specified address) followed by 16 CRC bits. The address field in the write protect
commands is a group address in byte units.
The card ignores all LSBs below the group size.
Mechanical write protect switch
A mechanical sliding tab on the side of the card allows the user to set or clear the write
protection on a card. When the sliding tab is positioned with the window open, the card is
write-protected, and when the window is closed, the card contents can be changed. A
matched switch on the socket side indicates to the SDIO card host module that the card is
write-protected. The SDIO card host module is responsible for protecting the card. The
position of the write protect switch is unknown to the internal circuitry of the card.
Password protect
The password protection feature enables the SDIO card host module to lock and unlock a
card with a password. The password is stored in the 128-bit PWD register and its size is set
in the 8-bit PWD_LEN register. These registers are nonvolatile so that a power cycle does
not erase them. Locked cards respond to and execute certain commands. This means that
the SDIO card host module is allowed to reset, initialize, select, and query for status,
however it is not allowed to access data on the card. When the password is set (as indicated
by a nonzero value of PWD_LEN), the card is locked automatically after power-up. As with
the CSD and CID register write commands, the lock/unlock commands are available in the
transfer state only. In this state, the command does not include an address argument and
the card must be selected before using it. The card lock/unlock commands have the
structure and bus transaction types of a regular single-block write command. The
transferred data block includes all of the required information for the command (the
password setting mode, the PWD itself, and card lock/unlock). The command data block
size is defined by the SDIO card host module before it sends the card lock/unlock
command, and has the structure shown in Table 115.
The bit settings are as follows:
• ERASE: setting it forces an erase operation. All other bits must be zero, and only the
command byte is sent
• LOCK_UNLOCK: setting it locks the card. LOCK_UNLOCK can be set simultaneously
with SET_PWD, however not with CLR_PWD
• CLR_PWD: setting it clears the password data
• SET_PWD: setting it saves the password data to memory
• PWD_LEN: it defines the length of the password in bytes
• PWD: the password (new or currently used, depending on the command)
The following sections list the command sequences to set/reset a password, lock/unlock the
card, and force an erase.
Setting the password
1. Select a card (SELECT/DESELECT_CARD, CMD7), if none is already selected.
2. Define the block length (SET_BLOCKLEN, CMD16) to send, given by the 8-bit card
lock/unlock mode, the 8-bit PWD_LEN, and the number of bytes of the new password.
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