Mechanical Write Protect Switch; Password Protect; Table 20-21 Structure Of Command Data Block - Motorola DragonBall MC9328MX1 Reference Manual

Multimedia Card/Secure Digital Host Controller Module (MMC/SD)
The
SEND_WRITE_PROT
containing 32 write protection bits (representing 32 write protect groups starting 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.

20.7.4.2 Mechanical Write Protect Switch

A mechanical sliding tab on the side of the card allows the user to set or clear 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 proper, matched switch on the socket side indicates to the MMC/SD module that the card is write
protected. The MMC/SD module is responsible for protecting the card. The position of the write protect
switch is unknown to the internal circuitry of the card.

20.7.4.3 Password Protect

The password protection feature enables the MMC/SD 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 non-volatile so that a power cycle does not erase them.
Locked cards respond to and execute certain commands. This means that the MMC/SD 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 on. As with the CSD and CID Register write commands, the lock/unlock commands are available in
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 MMC/SD module before it sends the card lock/unlock command, and has the
structure shown in Table 20-21.
Byte# Bit 7
0 Reserved
1
2
...
PWD_LEN +1
The bit settings are as follows:
ERASE—Setting forces an erase operation. All other bits must be zero, and only the command byte
•
is sent.
LOCK_UNLOCK—Setting locks the card. LOCK_UNLOCK can be set simultaneously with
•
SET_PWD, however not with CLR_PWD.
CLR_PWD—Setting clears the password data.
•
SET_PWD—Setting saves the password data to memory.
•
20-46
command is similar to a single block read command. The card sends a data block
Table 20-21. Structure of Command Data Block
Bit 6 Bit 5
Reserved Reserved
MC9328MX1 Reference Manual
Bit 4 Bit 3
Reserved ERASE LOCK_
UNLOCK
PWD_LEN
PWD
Bit 2 Bit 1 Bit 0
CLR_ SET_
PWD PWD
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