User Manual

Secure Digital (SD) Bus Protocol Description

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As described above for block write, the device 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 device or perform device

disconnection, as described in the Block Write section, above.

The data at the device after an erase operation is either ‘0’ or ‘1’, depending on the device vendor.

The SCR register bit DATA_STAT_AFTER_ERASE (bit 55) defines whether it is ‘0’ or ‘1’.

4.4.4. Write Protect Management

Two write protect methods are supported in the TriFlash as follows:

• Device internal write protect (device’s responsibility).

• Password protection device lock operation.

4.4.4.1. Device’s Internal Write Protection (Optional)

Device data may be protected against either erase or write. The entire device 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. Card Lock/Unlock

The Card Lock and Unlock features of the Secure Digital Card have been implemented in the TriFlash. Details on

how to use this feature are given in section 4.4.5 of the SD Memory Card Physical Layer Specification, version

1.01.

4.4.6. Application Specific Commands

The SD bus is defined to be protocol forward compatible to the MultiMediaCard Standard.

The SD bus 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 specific commands, the SD bus 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 device, will cause the device 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 device will recognize it as ACMD by the fact that it

appears after APP_CMD.

The only effect of the APP_CMD is that if the command index of the immediately following command has an

ACMD overloading it, the non-standard version will be used. For example, a device has a definition for ACMD13

but not for ACMD7. Therefore, if Command 13 is received immediately after APP_CMD command, it would be

interpreted as the non-standard ACMD13, whereas command 7, similarly received, would be interpreted as the

standard CMD7. In order to use one of the manufacturer specific ACMDs the host will: