Specifications

Physical Layer Simplified Specification Version 4.10

4.3.9 Application-Specific Commands

4.3.9.1 Application-Specific Command – APP_CMD (CMD55)

This command, when received by the card, causes the card to interpret the following command as an

application-specific command, ACMD. The ACMD provides command extension, has the same

structure as that of regular commands and it may have the same CMD number. The card recognizes it

as ACMD by the fact that it appears after APP_CMD.

When an ACMD is not defined, the card treats it as regular command. If, as an example, a card has a

definition for ACMD13 but not for ACMD7, then, command 13 after APP_CMD is interpreted as the

non-regular CMD13 but command 7 after APP_CMD is interpreted as the regular CMD7. In order to

use one of the ACMD's, the host should be:

(1) When sending APP_CMD, the response has the APP_CMD bit set signaling to the host that

ACMD is now expected.

(2) ACMD55 does not exist. If multiple CMD55 are issued continuously, APP_CMD bit in each

response is set to 1. The command issued immediately after the last CMD55 shall be interpreted

as ACMD. When more than one command (except CMD55) is issued directly after CMD55, the

first command is interpreted as ACMD and the following commands are interpreted as regular

commands

(3) If a defined ACMD is send and it is legal, the response has the APP_CMD bit set, indicating that

the accepted command is interpreted as ACMD.

(4) If an undefined ACMD is sent and it is legal, the response has the APP_CMD bit cleared,

indicating that the accepted command is interpreted as normal CMD.

(5) If a defined or undefined ACMD is sent and it is illegal, then it is handled as an illegal command.

Illegal Command Error is indicated in the next R1/R6 response and host should ignore APP_CMD

status in the response. Next command is handled as normal command.

Host shall not use undefined ACMDs as regular commands even if the specification defines it.

The following ACMD numbers are reserved for the SD Memory Card proprietary applications and shall

not be used by any SD Memory Card manufacturer:

ACMD6, ACMD13, ACMD17-26, ACMD38-49, ACMD51.

In above explanation, commands defined in the detailed command description section are "defined"

commands but not defined in the section are "Undefined" commands (Section 4.7.4 or Section 7.3.1.3

depends on bus mode). "Legal" means that a defined or undefined command is accepted at the current

state and "Illegal" means that a defined or undefined command is not accepted at the current state.

Exception in ACMD41

• The response of ACMD41 does not have APP_CMD status. Sending the response of CMD41 in

idle state means the card is accepted as legal ACMD41.

• As APP_CMD status is defined as "clear by read", APP_CMD status, which is set by ACMD41,

may be indicated in the response of next CMD11 or CMD3. However, as ACMD11 and ACMD3 are

not defined, it is not necessary to set APP_CMD status.

• Host should ignore APP_CMD status in the response of CMD11 and CMD3.

4.3.9.2 General Command - GEN_CMD (CMD56)

This section is a blank in the Simplified Specification.