Mass Storage Basics - USB Mass Storage: Designing and Programming Devices and Embedded Hosts - page 20

and its status, to send control information to a card, and to read and write
data in the storage media. An SPI host can use most of the MultiMediaCard
commands. Chapter 4 and Chapter 5 have more about MultiMediaCard
programming.
Fees
MultiMediaCard hosts have no licensing fees, but the MMCA charges to
download the specifications. At this writing, the cost is $500 for version 3.1
of the specification and $1000 for version 4.1, which adds the MMCmobile
and MMCplus variants. Those who join the MMCA at $2500/year get the
specifications for no additional charge plus other benefits.
SD Memory Card
Secure Digital (SD) Memory Cards, or SD Cards for short, are similar in
capability, size, and pinout to MultiMediaCards. An SD-Card host can
communicate with both MultiMediaCards and SD Cards.
Compared to MultiMediaCards, SD Cards have these differences:
• In the original form factors, SD Cards are thicker than MultiMediaCards
(2.1 mm versus 1.4 mm). Card connectors that accommodate both types
are available. With adapters, you can use any form factor of either card
type in a full-size SD-card connector.
• Some SD Cards have a manual write-protect switch.
• SD cards have additional registers with configuration and status informa-
tion.
• SD Cards support additional commands, including a command that
enables the host to specify a power-supply voltage.
• Unlike MultiMediaCards, SD Cards don't need to be clocked at 400 kHz
or less until the card is initialized (but doing so causes no harm).
The SD-Card technology was developed by Matsushita Electric Industrial
Co., Ltd., SanDisk Corporation, and Toshiba Corporation.
Packages
Table 1-4 compares the SD-Card variants. SD Cards are available in three
form factors: original SD Card, miniSD TM Card, and microSD TM Card (Fig-