Specifications

Physical Layer Simplified Specification Version 4.10

4.3.14 Command Functional Difference in Card Capacity Types

CCS in the response of ACMD41 determines card capacity types: CCS=0 is SDSC and CCS=1 is

SDHC or SDXC.

Memory access commands include block read commands (CMD17, CMD18), block write commands

(CMD24, CMD25), and block erase commands (CMD32, CMD33).

Following are the functional differences of memory access commands between SDSC and SDHC,

SDXC:

• Command Argument

SDHC and SDXC use the 32-bit argument of memory access commands as block address

format. Block length is fixed to 512 bytes regardless CMD16,

SDSC uses the 32-bit argument of memory access commands as byte address format. Block

length is determined by CMD16,

i.e.:

(a) Argument 0001h is byte address 0001h in the SDSC and 0001h block in SDHC and SDXC

(b) Argument 0200h is byte address 0200h in the SDSC and 0200h block in SDHC and SDXC

• Partial Access and Misalign Access

SDHC and SDXC disable Partial access and Misalign access (crossing physical block

boundary) as the block address is used. Access is only granted based on block addressing.

• Set Block Length

SDHC and SDXC use 512-byte fixed block length for memory access commands regardless of

the block length set by CMD16. The setting of the block length does not affect the memory

access commands. CMD42 is not classified as a memory access command. The data block

size shall be specified by CMD16 and the block length can be set up to 512 bytes. Setting

block length larger than 512 bytes sets the BLOCK_LEN_ERROR error bit regardless of the

card capacity.

• Write Protected Group

SDHC and SDXC do not support write-protected groups. Issuing CMD28, CMD29 and CMD30

generates the ILLEGAL_COMMAND error.