Write Protect Management; Mechanical Write Protect Switch; Card's Internal Write Protection (Optional); Application Specific Commands - SanDisk SDSDB-32-201-80 - Industrial Grade Flash Memory Card Product Manual

As described above for block write, the card will indicate that an erase is in progress by holding DAT0 low. The
actual erase time may be quite long, and the host may issue CMD7 to deselect the card or perform card
disconnection, as described in the Block Write section, above.
The data at the card after an erase operation is either '0' or '1', depending on the card vendor. The SCR register bit
DATA_STAT_AFTER_ERASE (bit 55) defines whether it is '0' or '1'.

4.4.4. Write Protect Management

Three write protect methods are supported in the SD Card as follows:
Mechanical write protect switch (Host responsibility only)
Card internal write protect (Card's responsibility)
Password protection card lock operation.

4.4.4.1. Mechanical Write Protect Switch

A mechanical sliding tablet on the side of the card (refer to the mechanical description) will be used by the user to
indicate that a given card is write protected or not. If the sliding tablet is positioned in such a way that the window is
open it means that the card is write protected. If the window is close the card is not write protected.
A proper, matched, switch on the socket side will indicate to the host that the card is write-protected or not. It is the
responsibility of the host to protect the card. The position of the write protect switch is un-known to the internal
circuitry of the card.

4.4.4.2. Card's Internal Write Protection (Optional)

Card data may be protected against either erase or write. The entire card may be permanently write-protected by the
manufacturer or content provider by setting the permanent or temporary write protect bits in the CSD.

4.4.5. Application Specific Commands

The SD Card is defined to be protocol forward compatible to the MultiMediaCard Standard.
The SD Card system is designed to provide a standard interface for a variety application types. In order to keep
future compatibility to the MultiMediaCard standard together with new SD Card specific commands, the SD Card
uses the Application Specific commands feature to implement its proprietary commands. Following is a description
of APP_CMD and GEN_CMD as they were defined in the MultiMediaCard Specification.
Application Specific Command—APP_CMD (CMD55)
This command, when received by the card, will cause the card to interpret the following command as an application
specific command (ACMD). The ACMD has the same structure as regular MultiMediaCard standard commands
and it may have the same CMD number. The card will recognize it as ACMD by the fact that it appears after
APP_CMD.
SanDisk Secure Digital (SD) Card Product Manual, Rev. 1.9 © 2003 SANDISK CORPORATION
Secure Digital (SD) Card Protocol Description
4-13