Specifications

Physical Layer Simplified Specification Version 4.10

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4.13.3 Speed Grade Specification for UHS-I and UHS-II

4.13.3.1 Speed Grade Parameters

4.13.3.1.1 UHS Speed Grade

Following grades are defined and indicated by UHS_SPEED_GRADE in SD Status. Speed Grade

may be supported in SDHC and SDXC. In case of UHS-II card supports Speed Grade 1, both UHS-I

mode and UHS-II mode shall support Speed Grade 1.

(1) Speed Grade 0: Performance is less than 10MB/sec

(2) Speed Grade 1: Performance is 10MB/sec and above

4.13.3.1.2 AU (Allocation Unit)

AU size of Speed Grade is specified by UHS_AU_SIZE in SD Status. The maximum AU size is

64MB. Card should indicate smaller AU Size as much as possible. Refer to Section 4.10.2 for more

details.

4.13.3.1.3 RU (Recording Unit)

RU size is 512KB.

4.13.3.1.4 Pw (Write Performance)

The definition of Pw is the same as SDXC. Refer to Section 4.13.2.2.

4.13.3.1.5 Pm (Performance Move)

Pm shall be treated as 0 regardless of the register value.

4.13.3.1.6 Pr and T

(4KB) (Read Performance)

The definition of Pr and T

(4KB) are the same as SDXC. Refer to Section 4.13.2.3.

4.13.3.1.7 UHS-II Parameters

Host may use any N_FCU size to use Speed Grade 1.

Speed Grade is not supported in 2L-HD Mode or Low Power Mode.

4.13.3.2 Support of Speed Class Control Command (CMD20)

With regard to Speed Grade 1 supported Host and Card, support of CMD20 is mandatory for SDXC

and optional for SDHC. In order to maintain backward compatibility, Speed Grade 1 SDHC cards

shall support Speed Class and Speed Grade 1 without the host indication of CMD20.