SanDisk Secure Digital (SD) Card Product Manual, Rev. 1.9 © 2003 SANDISK CORPORATION
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Appendix A. Application Note
Host Design Considerations: NAND MMC and SD-based Products
Introduction
SanDisk’s MultiMediaCard (MMC) and Secure Digital (SD) Card have been designed into a wide variety of
consumer electronic products: MP3 players, cell phones, PDAs, digital still and video cameras, data loggers, and
more. Although these cards were designed to support this wide range of products, there are many options an
engineer needs to consider before designing a card slot into a product. Design considerations include how the end
product handles timeout delays, bus type selection, block mode selection, and other options. These can have a
major impact on the performance and compatibility of the product. This Application Note will review these options
and provide recommendations on the optimum way to manage them.
Timing
There are important timing issues for the engineer to consider when designing products that integrate the
MultiMediaCard and/or SD Card.
Timing specifications
Design engineers must meet the rise, fall, setup, hold, and other SD Card and MultiMediaCard bus timing
specifications. If they want to support MultiMediaCards in their design, the clock speed should be controllable by
the host. This is due to the MultiMediaCard's open-drain mode; the MultiMediaCard powers up in the open-drain
mode and cannot handle a clock faster than 400 Khz. Once the MultiMediaCard completes the initialization
process, the card switches to the push-pull mode. In the push-pull mode the MultiMediaCard can run at the
maximum clock speed.
Refer to
www.mmca.org
and
www.sdcard.org
for timing specifications published by MultiMediaCard and
SD Card Associations.
Read access and program times
Read access and program times are also very critical to the proper operation of a product design. If the time-out
values for read access and program time are not met, data read from and written to the card may be incorrect or
invalid. MultiMediaCard and SD Card manufacturers have different read and write time-out values, and the
designer must ensure that the product time-out value is not set below the maximum specification.
The maximum read and write time-out values for the MultiMediaCard and SD Card are shown in Table 1.
Table 1.
MultiMediaCard and SD Card Maximum Read/Write Time-out Values
Product Time-out
Values
MultiMediaCard Typical
Maximum
Read
(TAAC + NSAC)
10 * (TAAC + NSAC)
Write
(TAAC + NSAC) * R2W_FACTOR
(TAAC) + NSAC) * R2W_FACTOR * 10
SD Card
