16. MultiMedia Card Controller
The AT89C5132 implements a MultiMedia Card (MMC) controller. The MMC is used to store
files in removable Flash memory cards that can be easily plugged or removed from the
application.
16.1 Card Concept
The basic MultiMedia Card concept is based on transferring data via a minimal number of
signals.
16.1.1
Card Signals
The communication signals are:
•
CLK: with each cycle of this signal an one bit transfer on the command and data lines is
done. The frequency may vary from zero to the maximum clock frequency.
•
CMD: is a bidirectional command channel used for card initialization and data transfer
commands. The CMD signal has two operation modes: open-drain for initialization mode
and push-pull for fast command transfer. Commands are sent from the MultiMedia Card bus
master to the card and responses from the cards to the host.
•
DAT: is a bidirectional data channel. The DAT signal operates in push-pull mode. Only one
card or the host is driving this signal at a time.
16.1.2
Card Registers
Within the card interface five registers are defined: OCR, CID, CSD, RCA and DSR. These can
be accessed only by corresponding commands.
The 32-bit Operation Conditions Register (OCR) stores the VDD voltage profile of the card. The
register is optional and can be read only.
The 128-bit wide CID register carries the card identification information (Card ID) used during
the card identification procedure.
The 128-bit wide Card-Specific Data register (CSD) provides information on how to access the
card contents. The CSD defines the data format, error correction type, maximum data access
time, data transfer speed, and whether the DSR register can be used.
The 16-bit Relative Card Address register (RCA) carries the card address assigned by the host
during the card identification. This address is used for the addressed host-card communication
after the card identification procedure
The 16-bit Driver Stage Register (DSR) can be optionally used to improve the bus performance
for extended operating conditions (depending on parameters like bus length, transfer rate or
number of cards).
16.2 Bus Concept
The MultiMedia Card bus is designed to connect either solid-state mass-storage memory or I/O-
devices in a card format to multimedia applications. The bus implementation allows the cover-
age of application fields from low-cost systems to systems with a fast data transfer rate. It is a
single master bus with a variable number of slaves. The MultiMedia Card bus master is the bus
controller and each slave is either a single mass storage card (with possibly different technolo-
gies such as ROM, OTP, Flash etc.) or an I/O-card with its own controlling unit (on card) to
perform the data transfer.
The MultiMedia Card bus also includes power connections to supply the cards.
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AT89C5132
4173E–USB–09/07
ATMEL [ ATMEL ]
