SanDisk SD Card

Revision 2.2Chapter 4 – SD Card Protocol DescriptionSanDisk SD Card Product ManualMechanical Write Protect SwitchA mechanical sliding tablet on the side of the card (refer to the mechanical description),controlled by the user, indicates whether or not a given card is write-protected. If thesliding tablet is in the position of the window open, it means the card is write-protected. Ifthe window is closed, the card is not write-protected.A proper, matched, switch on the socket side will indicate to the host that the card is writeprotectedor not. It is the responsibility of the host to protect the card. The position of thewrite-protect switch is unknown to the internal circuitry of the card.Card’s Internal Write Protection (Optional)Card data may be protected against either erase or write. The entire card may bepermanently write-protected by the manufacturer or content provider by setting thepermanent or temporary write protect bits in the CSD Register.4.4.7 Card Lock/Unlock OperationThe password-protection feature enables the host to lock a card while providing a passwordthat will be used later for unlocking the card. The password and its size are kept in 128-bitPWD and 8-bit PWD_LEN registers, respectively. These registers are non-volatile whichprotects a power cycle erase.Locked cards respond to (and execute) all commands in the "basic" command class (class0), ACMD41, CMD16 and “lock card” command class. Thus the host is allowed to reset,initialize, select, query for status, etc., but not to access data on the card. If the passwordwas previously set (the value of PWD_LEN is not ‘0’), it will be locked automatically afterpower on.Similar to the existing CSD Register write commands the lock/unlock command isavailable in "transfer state" only. This means that it does not include an address argumentand the card has to be selected before using it.The card lock/unlock command has the structure and bus transaction type of a regularsingle block write command. The transferred data block includes all the requiredinformation of the command (password setting mode, PWD itself, card lock/unlock etc.).The following table describes the structure of the command data block.Table 4-3Lock Card Data StructureByteBit7Bit6Bit5Bit4Bit 3 Bit 2 Bit 1 Bit 00 Reserved ERASE LOCK_UNLOCK CLR_PWD SET_PWD1 PWDS_LEN2…PWDS_LEN+ 1Password Data© 2004 SanDisk Corporation 4-12 12/08/04