Rainbow Electronics AT89C5132 - Manual (Page 82)

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AT8xC5132
4173A–8051–08/02
MultiMedia Card
Controller
The AT8xC5132 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.
Card Concept The basic MultiMedia Card concept is based on transferring data via a minimal number
of signals.
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.
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 V
DD
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, maxi-
mum 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 per-
formance for extended operating conditions (depending on parameters like bus length,
transfer rate or number of cards).
Bus Concept The MultiMedia Card bus is designed to connect either solid-state mass-storage mem-
ory or I/O-devices in a card format to multimedia applications. The bus implementation
allows the coverage 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 Multi-
Media Card bus master is the bus controller and each slave is either a single mass
storage card (with possibly different technologies 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.
The bus communication uses a special protocol (MultiMedia Card bus protocol) which is
applicable for all devices. Therefore, the payload data transfer between the host and the
cards can be bidirectional.