Host Design Considerations: Application Note
NAND MMC and SD-based Products Revision 1.0
© 2002 SanDisk Corporation 3 9/30/02, Lit# 80-11-00160
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.
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