Specifications

©Copyright 2001-2013 SD Group (Panasonic, SanDisk, Toshiba) and SD Card Association
Physical Layer Simplified Specification Version 4.10
98
4.13.1.7.1 Measurement Condition to determine Average T
Fw
The equation (4) defines Average FAT Write Time (T
FW
(ave.)), which is the maximum sliding average
of 8 times FAT write cycles.
Average FAT Write Time:
8
))(max(
.)(
8
1
∑
=
=
i
FW
FW
iT
aveT
...............................................(4)
4.13.1.7.2 Maximum FAT Write Time
During a FAT update, the host cannot write data to the card. Therefore, the host should prepare enough
buffers to save the data temporarily. The Maximum FAT Write Time (T
FW
(max.)) is one of the factors
to determine host buffer size. During 8 times FAT write cycle, occurrence of T
FW
(max.) should not
appear more than once. On the method of Host Buffer Size estimation, refer to the Implementation
Guideline of the Speed Class Specification.
Maximum FAT Write Time:
msT
FW
750.)(max ≤
...........................................................(5)
4.13.1.8 Measurement Conditions and Requirements of the Speed Class
4.13.1.8.1 Measurement Conditions
Table 4-56 shows measurement conditions for each Speed Class. The Speed Class 10 card shall
support high speed mode. The higher Speed Class may require higher frequency or larger RU size.
These values provide margin for host applications running at maximum speed.
Card Capacity
SDSC
SDHC
~64MB
~256MB
~512MB
~1GB
~2GB
~32GB
AU Size (max.)
512KB
1MB
2MB
4MB
RU Size
Class2, 4
16KB
32KB
Class6
64KB
Class 10
Not Supported
512KB
Notes: Class 2 to 6 are measured at 20MHz in Default Speed Mode
Class 10 is measured at 40MHz in High Speed Mode
Table 4-56: Measurement Condition of Speed Class (SDSC and SDHC)
Application Note:
The minimum performance is measured at 100% usage rate of the SD Bus (No idle time is assumed
in accesses). Therefore, writing to the card at intervals decreases performance.
Host needs to use higher frequency clock than that of measurement condition.
4.13.1.8.2 Requirements of the Performance Parameters for Each Speed Class
Table 4-57 identifies the requirement of the parameters for each class under measurement conditions.
All conditions of any Class should apply simultaneously. Any cards having a specific Speed Class shall
also satisfy the requirements and conditions of lower Classes. For example, Class 6 card shall satisfy
Class 4 performance under Class 4 condition. Class 10 card shall satisfy Class 6 performance under
the Class 6 conditions and Class 4 performance under the Class 4 conditions (Class 4 always covers
Class 2 because of using the same conditions).
Regarding Class 10 Card, as Class 10 mode does not support Pm, the minimum requirement of Pm is
more than or equal to 2MB/sec under the Class 4 conditions and 3MB/sec under the Class 6 conditions
even if PERFORMANCE_MOVE in SD Status is set to 0.