Freescale Semiconductor

Application Note

Document Number: AN2689

Rev. 1, 10/2005

1Abstract

The MultimediaCard™ (MMC) is a low cost data

storage and communication medium implemented as a

hardware card with a simple control unit and a compact,

easy-to-implement interface that is designed to cover a

wide variety of applications. MMC communication is

based on an advanced 7-pin serial bus designed to

operate in a low voltage range at medium speed. Secure

Digital Card (SD) is an evolution of the MMC with an

additional two pins in the form factor that is specifically

designed to meet the security, capacity, performance, and

environmental requirements inherent in new audio and

video consumer electronic devices. The physical form

factor, pin assignment, and data transfer protocol are

compatible with the MMC. The SD is composed of a

memory card and an I/O card. The I/O card combines

high-speed data input/output with low-power

consumption for mobile electronic devices.

The MMC/SD physical specifications support two

operation modes, SD transfer mode and SPI transfer

mode. The Multimedia Card/Secure Digital Host

Controller (SDHC) designed in the i.MX processors

Using SDIO with SDHC

MC9328MX1, MC9328MXL, and MC9328MXS

Contents

1 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

2 Modes of Operation . . . . . . . . . . . . . . . . . . . . . . .2

3 Hardware Consideration

on using SPI Transfer Mode . . . . . . . . . . . . . . . .4

4 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

5 Revision History . . . . . . . . . . . . . . . . . . . . . . . . . .8

This document applies to the following i.MX

devices, collectively called i.MX throughout:

• MC9328MX1

• MC9328MXL

• MC9328MXS

Modes of Operation

Using SDIO with SDHC Application Note, Rev. 1

2 Freescale Semiconductor

integrate MMC support with SD memory and, I/O functions. The I/O function supported follows the SPI

transfer mode. However, the SPI mode relies on the i.MX processor’s embedded SPI module. The

disadvantage of using the SPI is the loss of performance of the SPI transfer mode versus SD transfer mode

(for example a single data line and hardware Chip Select signal per card). This application note attempts

to resolve the I/O and socket connections issue.

2 Modes of Operation

The two transfer modes of operation are discussed in this section.

2.1 SD Transfer Mode Operation

The Secure Memory Card bus has a single master (application), multiple slaves (cards), synchronous star

topology (see Figure 1). Clock, power, and ground signals are common to all cards. Command (CMD) and

data (DAT0–DAT3) signals are dedicated to each card to provide continued point-to-point connection to

all cards. During the initialization process, commands are sent to each card individually, allowing the

application to detect the cards and to assign logical addresses to the physical slots. Data is always sent or

received–to or from each card individually. However, to simplify the handling of the card stack after the

initialization process, all commands may be sent concurrently to all cards. Addressing information is

provided in the command packet.

SD bus allows dynamic configuration of the number of data lines. After power-up, by default, the SD

Memory Card will use only DAT0 for data transfer. After initialization the host can change the bus width

(number of active data lines). This feature allows easy trade-off between hardware cost and the system.

The SD bus includes the following signals:

• CLK: Host to card clock signal

• CMD: Bidirectional Command/Response signal

• DAT0–DAT3: Four bi-directional data signals

• VDD, VSS1, VSS2: Power and ground signals