User Manual

Secure Digital (SD) Bus Protocol Description

• Send APP_CMD. The response will have the APP_CMD bit (new status bit) set signaling to the host

that ACMD is now expected.

• Send the required ACMD. The response will have the APP_CMD bit set, indicating that the accepted

command was interpreted as ACMD. If a non-ACMD is sent then it will be respected by the card as

normal SD command and the APP_CMD bit in the Card Status stays clear.

If an invalid command is sent (neither ACMD nor CMD) then it will be handled as a standard SD illegal command

error.

From the SD bus protocol point of view the ACMD numbers will be defined by the manufacturers with some

restrictions. The following ACMD numbers are reserved for the SD proprietary applications and may not be used by

any TriFlash manufacturer:

ACMD6, ACMD13, ACMD17-25, ACMD38-49, ACMD51.

General Command—GEN_CMD (CMD56)

The bus transaction of the GEN_CMD is the same as the single block read or write commands (CMD24 or

CMD17). The difference is that the argument denotes the direction of the data transfer (rather than the address) and

the data block is not memory payload data but has a vendor specific format and meaning. The device shall be

selected (‘tran_state’) before sending CMD56. The data block size is the BLOCK_LEN that was defined with

CMD16. The response to CMD56 will be R1.

Currently, there are no defined commands or usage for CMD56 in SanDisk’s TriFlash, but new commands may be

easily defined and tailored for OEM application specific requirements (upon request to SanDisk).

4.5. Clock Control

The SD Bus clock signal can be used by the TriFlash host to set the devices to energy saving mode or to control the

data flow on the bus. The host is allowed to lower the clock frequency or shut it down.

There are a few restrictions the TriFlash host must follow:

• The bus frequency can be changed at any time (under the restrictions of maximum data transfer

frequency, defined by the TriFlash and the identification frequency).

• An exception to the above is ACMD41(SD_APP_OP_COND). After issuing command ACMD41, the

following 1 or 2 procedures shall be done by the host until the device becomes ready.

− Issue continuous clock in frequency range of 100KHz-400KHz.

− If the host wants to stop the clock, poll busy bit by ACMD41 command at less than 50ms

intervals.