Analog Devices EE264v01 Application Notes

Engineer-to-Engineer Note EE-264

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Interfacing MultiMediaCard™ with ADSP-2126x SHARC® Processors

Contributed by Aseem Vasudev Prabhugaonkar and Jagadeesh Rayala Rev 1 – March 11, 2005

Introduction

This application note describes how to
implement the interface between an ADSP­2126x SHARC® processor and a
MultiMediaCard™ (MMC). The application note
also describes the MMC command format and
demonstrates with example code how an MMC
card can be interfaced seamlessly with the
SHARC processor’s SPI port. Example code
supplied with this application note implements
the most commonly used commands of
MultiMediaCard.

About MultiMediaCard

memory access voltage of 2.7 to 3.6 V, and a
capacity from 4 MB to the gigabyte range.

About the ADSP-2126x SPI Port

The ADSP-2126x processor is equipped with a
synchronous serial peripheral interface port that
is compatible with the industry-standard Serial
Peripheral Interface (SPI). The SPI port supports
communication with a variety of peripheral
devices including codecs, data converters,
sample rate converters, S/PDIF or AES/EBU
digital audio transmitters and receivers, LCDs,
shift registers, micro-controllers, and FPGA
devices with SPI emulation capabilities.

The MMC was introduced in 1998 and had an
amazing reduction in cubic capacity compared
with CompactFlash™. MMC cards are now
widely used in digital cameras, smart cell

Important features of ADSP-2126x SPI port
include:

 Simple four-wire interface, consisting of two

data pins, a device select pin, and a clock pin

phones, PDAs, and portable MP3 players. Their
intended use is to store information and content.

 Full duplex operation, allowing simultaneous

data transmission and reception on the same

The MMC consists of a 7-pin interface and

SPI port

supports two serial data transfer protocols viz.
the MMC (MultiMediaCard) mode and SPI
(Serial Peripheral Interface) mode. The
maximum operating clock frequency used for
serial communication in both modes can go up to
20 MHz. The data written in any of these modes
can be read by host in either mode. The
advantage of MMC supporting SPI mode is that
MMC can be interfaced seamlessly to many
controllers or DSP processors, which have on­chip support for SPI. Most MMCs have a

 Data formats to accommodate little and big

endian data, different word lengths, and
packing modes

 Master and slave modes as well as

multimaster mode in which the ADSP-2126x
processor can be connected to up to four other
SPI devices

 Open drain outputs to avoid data contention

and to support multimaster scenarios

communication voltage from 2.0 to 3.6 V, a

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 Programmable bit rates, clock polarities, and

phases

 DMA capability, allowing transfer of data

without core overhead

 Master or slave booting from a master SPI

device

The MultiMediaCard Interface

In SPI mode, four signals (clock, data in, data out
and chip select) are used for the interface. The
clock is used to drive data out on the data out pin
and receive data on the data in pin. The host
drives commands and data to the MMC over the
MMC’s data in pin. The host receives response
and data from the MMC on its data out pin. The
chip select signal is used to enable the MMC
during data and command transfer. The chip
select signal is also used initially to drive the
MMC in SPI mode. Note that in SPI mode, data
is transferred in units of eight clock cycles.

Pin Name Type Function

1 CS# Input Chip select

(active low)
2 Din Input Data input
3 VSS1 Power GND
4 VDD Power VCC
5 CLK Input Clock input
6 VSS2 Power GND
7 Dout Output Data output

Table 1. MultiMediaCard Pin Assignment

The MMC pin assignments in SPI mode are
shown in Table 1 and Figure 1. Figure 2 shows
the MMC interface with the ADSP-2126x SPI
port.

VCC

ADSP-2126x
SPI

MOSI

MISO

SPICLK

FLAGx

Figure 2. MultiMediaCard Interface with SPI Port

Din
Dout
CLK

GND

The MultiMediaCard Protocol

The SHARC processor's SPI issues commands to
the MMC over the data in (Din) pin of the MMC.
The data in pin of the MMC is connected to MOSI
of the SPI. The data is also written to the MMC
over the data in signal of the MMC. Based on the
received command, the MMC sends response or
data on the data out (Dout) pin. The data out pin
of the MMC is connected to MISO of the SHARC
processor's SPI port. The processor's SPI port
uses one of the Programmable Flag pins (FLAGx)
to drive CS# of the MMC. The communication is
initiated by different commands sent from the
SHARC processor to the MMC. All commands
are six bytes long and are transmitted MSB first.
Refer to Figure 3 for generic transfer protocol
between the MMC and the SHARC processor's
SPI port.

Figure 1. MultiMediaCard Pin Assignments

Interfacing MultiMediaCard™ with ADSP-2126x SHARC® Processors (EE-264) Page 2 of 6

Figure 3. MultiMediaCard Transfer Protocol