NXP Semiconductors MC9328MX1 Manuale

Freescale Semiconductor

Application Note

Document Number: AN3049

Rev. 0, 10/2005

1Abstract

This document describes the Multimedia Card (MMC)

and the Secure Digital (SD) modules on Freescale

Semiconductor’s i.MX application processors. This

document gives an overview of the similarities and

differences of both the MMC and SD protocols and

cards including configuration of the MMC/SD module.

The document also describes the interface of the

MMC/SD modules, specifically the card identification

mode and the system clock controller, along with

example code. System considerations at various data

transfer rates are included.

This document applies to the following devices,

collectively called i.MX throughout:

• MC9328MX1

• MC9328MXL

• MC9328MX21

Setup and Use of the Multimedia

Card/Secure Digital Host Controller

MC9328MX1, MC9328MXL, and MC9328MX21

by: Jason Castillo

Contents

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

2 MMC/SD Module Overview . . . . . . . . . . . . . . . . . 2

3 MMC/SD Module Configuration . . . . . . . . . . . . . .2

4 Interfacing with the MMC/SD Module . . . . . . . . .5

5 Special Considerations . . . . . . . . . . . . . . . . . . .10

6 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11

MMC/SD Module Overview

Setup and Use of the Multimedia Card/Secure Digital Host Controller Application Note, Rev. 0

2Freescale Semiconductor

2 MMC/SD Module Overview

This section provides an overview of both the Multimedia Card (MMC) and Secure Digital Card (SD)

modules. The MMC/SD module includes the following features:

• Supports up to 10 cards (including one SD card)

• Password protection for cards

• Built-in programmable frequency counter for MMC/SD bus

• Maskable hardware interrupt for card detection (insertion/removal), SD I/O interrupt, internal

status, and FIFO status

• Contains an integrated 32 ×16-bit FIFO

• Supports plug-and-play (Pop)

• Supports many SD functions including multiple I/O and combined I/O and memory

• Supports up to seven I/O functions plus one memory on a single SD I/O card

• Card can interrupt MMC/SD module

• Support single or multiple block access, or stream access to the card for read, write, or erase

operations

• Supports SD I/O ReadWait and interrupt detection during 1- or 4-bit access

2.1 Multimedia Card (MMC) Protocol

The MMC is 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. It is based on an advanced 7-pin serial bus designed to operate over a voltage range of 2.0 to

3.6 V. Note that the maximum operating voltage range for the i.MX is 3.3 V. Therefore the i.MX-based

design is limited to a supply range of 2.0 to 3.3 V.

2.2 Secure Digital Card (SD) Protocol

The SD is an extended version of the MMC with two additional pins. The additional pins are designed to

meet the security, capacity, performance, and environmental requirements inherent in new audio and

video consumer electronic devices. The physical form factor and data transfer protocol are compatible

with the MMC. The SD is composed of a memory card and an I/O card.

3 MMC/SD Module Configuration

The MMC card has 7 pins and the SD card has 9 pins. The pins are used to communicate with other

functions within the card. The pin assignment and form factor are shown in Table 1.

MMC/SD Module Configuration

Setup and Use of the Multimedia Card/Secure Digital Host Controller Application Note, Rev. 0

Freescale Semiconductor 3

Table 1. MMC/SD Card Pin Assignment

Each card has a set of information registers that hold the operating parameters and other card conditions.

See the description in Table 2. Details of each register can be found in card registers chapter in both the

MultiMediaCard System Specification and the SD Memory Card Specification.

Table 2. MMC/SD Card Registers

MMC or SD Identifier Register Name Description Size

(Bits)

Both CID Card Identification Number Each card has a unique CID. 1281

1There can be fewer bits for the SD I/O Card, depending on implementation.

Both RCA Relative Card Address Assigned by the MMC/SD module during initialization. 16

Both DSR Driver Stage Configures the card’s output drivers. Use is optional, not

required.

Both CSD Card Specific Data Contains information on the card’s operating conditions. 1281

Both OCR Operation Conditions Indicates the card’s operating voltage range. Detects restricted

cards and indicates whether power-up is complete. Use is

optional, not required.

Both CSR Card Status Register Contains card’s error and status information. Sent to the

MMC/SD module in response format R1.

SD only SCS SD Card Status Contains status information proprietary to the SD card (such as

protection, card type, and bus width).

512

SD only SCR SD Configuration Register Contains additional configuration information only applicable to

the SD card.

MMC/SD Module Configuration

Setup and Use of the Multimedia Card/Secure Digital Host Controller Application Note, Rev. 0

4Freescale Semiconductor

3.1 Pin Configuration

The MMC/SD module uses six I/O pins to communicate with external MMC/SD cards.

•SD_CMD—Bidirectional command/response signal between the MMC/SD module and the card.

Open-drain for initialization state and push-pull for fast command transfers.

•SD_Clk—MMC/SD module to card clock signal (output).

•SD_DAT [3:0]—Four bidirectional data signals. When in push-pull mode, one card or the

MMC/SD module can drive each line at a time.

These six I/O pins are multiplexed with other functions on the i.MX devices and must be configured for

MMC/SD module operation. Explanation of the pin configuration can be found in the reference manual.

Example 1 is code sample of the pin configuration. The data direction register (DDIR) is not necessarily

required to initialize, however, it is highly recommended, especially when working with multiple

modules.

Example 1. Pin Configuration for MMC/SD Card on the i.MX1/L

/**************** Initialize ****************/

/* Set up GPIO for MMC/SD */

/********************************************/

void MMC_SD_Port_Initialize()

{

// SD_CMD - Primary function of GPIO Port B [13]

GIUS_B &= ~0x00002000; // CLEAR BIT 13

GPR_B &= ~0x00002000; // CLEAR BIT 13

PUEN_B |= 0x00002000; // SET BIT 13

// SD_CLK - Primary function of GPIO Port B [12]

GIUS_B &= ~0x00001000; // CLEAR BIT 12

GPR_B &= ~0x00001000; // CLEAR BIT 12

// SD_DAT[3] - Primary function of GPIO Port B [11]

GIUS_B &= ~0x00000800; // CLEAR BIT 11

GPR_B &= ~0x00000800; // CLEAR BIT 11

// SD_DAT[2] - Primary function of GPIO Port B [10]

GIUS_B &= ~0x00000400; // CLEAR BIT 10

GPR_B &= ~0x00000400; // CLEAR BIT 10

PUEN_B |= 0x00000400; // SET BIT 10

// SD_DAT[1] - Primary function of GPIO Port B [9]

GIUS_B &= ~0x00000200; // CLEAR BIT 9

GPR_B &= ~0x00000200; // CLEAR BIT 9

PUEN_B |= 0x00000200; // SET BIT 9

// SD_DAT[0] - Primary function of GPIO Port B [8]

GIUS_B &= ~0x00000100; // CLEAR BIT 8

GPR_B &= ~0x00000100; // CLEAR BIT 8

PUEN_B |= 0x00000100; // SET BIT 8

DDIR_B |= 0x00003F00; // Initialize SDHC's port

GPCR &= 0xFFFFF3FF; // DS_SLOW = 26 MHz / 15 pF

Interfacing with the MMC/SD Module

Setup and Use of the Multimedia Card/Secure Digital Host Controller Application Note, Rev. 0

Freescale Semiconductor 5

// GPCR |= 0x00000400; // DS_SLOW = 26 MHz / 30 pF

// GPCR |= 0x00000800; // DS_SLOW = 26 MHz / 45 pF

// GPCR |= 0x00000C00; // DS_SLOW = 26 MHz / greater than 45 pF

/*****************************************/

/* Include the AIPI Module Configuration */

/*****************************************/

PSR0_2 &= ~0x00000010;

PSR1_2 |= 0x00000010;

PAR_2 |= 0x00000010;

}

Notice in the code sample that the last five registers are included within the pin configuration. The DDIR

can have two SDHC ports, set both PTB_DDIR and PTE_DDIR registers to 0x000003F0 and

0x00FC0000 respectively. The GPCR is the peripheral control register which is used to control the

driving strength. When using the MMC/SD module the driving strength must be set to 15 pF; otherwise

overshoot and ringing problems can occur on the SD_CLK. Setting the driving strength on the i.MX21 is

explained in the driving strength section of reference [6]. The next three registers (PSR0_2, PSR1_2, and

PAR_2) are used to allow the IP bus peripheral to send 32 bits and whether it can be accessed in user

mode.

4 Interfacing with the MMC/SD Module

This section describes the different functional aspects of the MMC/SD module.

4.1 Card Identification Modes

The MMC/SD module is in identification mode after reset and during the search for new cards on the bus.

During the identification mode, the MMC/SD module performs the following steps which are explained

in more detail in the next sections:

1. Detects the cards

2. Resets all cards that are in the card identification state

3. Validates operation voltage range

4. Identifies the cards

5. Asks each card (separately, on its own SD_CMD line) to publish its relative card address (RCA)

4.1.1 Card Detect

Card detection occurs automatically through the SD_DAT [3] pin. Only the SD card has this feature

because the MMC does not have the SD_DAT [3] pin. The detection circuitry is sampled by the i.MX

system clock (HCLK) so the state of the MMC/SD module does not matter. After the card is detected, the

user must mask the card detection interrupt (INT_MASK |= 0x40) to avoid misleading interrupt

generation during card access as the SD_DAT lines change.

Interfacing with the MMC/SD Module

Setup and Use of the Multimedia Card/Secure Digital Host Controller Application Note, Rev. 0

6Freescale Semiconductor

4.1.2 Reset

When the i.MX is powered up, all cards (including the cards having been in inactive state) are in idle

state. Sending the command GO_IDLE_STATE (CMD0) also sets all cards into idle state. After the cards

are reset through the hardware or software (CMD0):

• All cards’ output bus drivers are in high-impedance state

• The cards are initialized with a relative card address (RCA) of 0x0001

• The cards are configured with a default driver stage register setting (lowest speed, highest driving

current capability).

In identification mode, low frequency is required for MMC cards (0 – 400 kHz).

4.1.3 Voltage Validation

All valid cards should be able to establish communication with the processor. If the card is not compatible

with the valid VDD range, the card will not be able to complete the identification mode.

SD_APP_OP_COND (ACMD41) is a special command for the SD cards to identify and reject cards that

are not within the VDD range. Because SD_APP_OP_COND is an application command, APP_CMD

(CMD55) must precede ACMD41.

MMC cards do not respond to CMD55. To recognize the MMC card, first send CMD55 and confirm

whether a time-out has occurred. If a time-out has occurred, then check for the MMC card by sending the

SEND_OP_COND (CMD1) command and check again for a time-out. If a time-out occurs after CMD1

then the following possibilities may have occurred:

1. No card present or incorrectly installed

2. Card does not meet the valid VDD range

3. Frequency is greater than 400 kHz

4.1.4 Card Registry

After validating the voltage for the card(s) and activating the bus, the module requests the card(s) to send

their operation conditions before going to the identification state. To request the operation conditions for

the card(s), the user must send the commands CMD55 followed by ACMD41 for the SD cards. For the

MMC cards the user must send the command CMD1. Afterwards the user must send CMD2 to each card

to get its unique card identification (CID) number. The last step is to send the SEND_RELATIVE_ADDR

(CMD3) command to publish a new relative card address. After the new RCA has been published the

state changes to standby state and the output switches from open-drain to push-pull. The RCA is used in

the data transfer mode.

4.2 System Clock Controller

Two clock stages are used in the MMC/SD module to maximize the power-saving capabilities. The input

clock operates around 20–100 MHz and passes through a prescaler that adjusts the inner clock under

20 MHz, which is the maximum operation frequency of the module. This clock is then passed through a

user-programmable clock divider. The divider is used to program the final MMC/SD bus clock for

Interfacing with the MMC/SD Module

Setup and Use of the Multimedia Card/Secure Digital Host Controller Application Note, Rev. 0

Freescale Semiconductor 7

different card applications. The resulting clock is used throughout the module. Figure 1 illustrates the

clock controller module.

Figure 1. i.MX1/L Clock Controller Module (MMC/SD uses PERCLK2 Signal)

To set the clock controller to desire frequency, you must configure the clock controller register: CSCR,

PCDR, MPCTL0, MPCTL1, SPCTL0, and SPCTL1. Example 2 is a code sample to configure the clock

with an output frequency of 406.25 kHz. For the i.MX21 there is an extra gate used for each peripheral

clock to conserve power when other peripherals are not in use. The extra gate is not shown in the code

example.

Example 2. Clock Controller Initialization for i.MX1/L

//----------------------------- Set up premultiplier PLL ------------------------------//

/* CLKO_SEL[31:29] = HCLK (CLKO pin)

* USB_DIV[28:26] = 000

* SD_CNT[25:24 = 00

* SPLL_RESTART[22] = RESTARTS SYSTEM PLL AT NEW FREQUENCY (0)

* MPLL_RESTART[21] = RESTARTS MCU PLL AT NEW FREQUENCY (0)

* CLK16_SEL[18] = 0

* OSC_EN[17] = 0

* SYSTEM_SEL[16] = CLOCK SOURCE IS THE INTERNAL PREMULTIPLIER

* PRESC[15] = PRESCALER DIVIDES BY 2

* BLCK_DIV[13:10] = SYSTEM PLLCLK DIVIDED BY 1

* SPEN[1] = SYSTEM PLL ENABLED

* MPEN[0] = MCU PLL ENABLED

Interfacing with the MMC/SD Module

Setup and Use of the Multimedia Card/Secure Digital Host Controller Application Note, Rev. 0

8Freescale Semiconductor

CSCR = 0x20008003;

PCDR = 0x0; /* PERCLK2 feeding SD = Sys PLL(16.384) divided by 1 */

//-------------------------------------------------------------------------------------//

//------------------------------- Set up Digital PLL ----------------------------------//

// NOTE: Digital PLL (DPLL) consists of both the MCU PLL and System PLL

// Input Frequency = 16.384 MHz

// MFI = 5; MFN = 46; MFD = 82; PD = 13

// Actual Tolerance = 0.000323%

// Actual Frequency = 13.000042 MHz

MPCTL0 = 0x3452142e;

SPCTL0 = 0x3452142e;

MPCTL1 = 0;

SPCTL1 = 0x00008000;

CSCR |= 0x600000;

// CLK_RATE = 0x0: CLK_DIV = CLK_20M = 13 MHz

// CLK_RATE = 0x1: CLK_DIV = 13/2 MHz = 6.5 MHz

// CLK_RATE = 0x2: CLK_DIV = 13/4 MHz = 3.25 MHz

// CLK_RATE = 0x3: CLK_DIV = 13/8 MHz = 1.625 MHz

// CLK_RATE = 0x4: CLK_DIV = 13/16 MHz = 812.5 KHz

// CLK_RATE = 0x5: CLK_DIV = 13/32 MHz = 406.25 kHz

// CLK_RATE = 0x6: CLK_DIV = 13/64 MHz = 203.125 kHz

// CLK_RATE = 0x7: CLK_DIV = 13/128 MHz = 101.563 kHz

CLK_RATE = 0x5;

4.3 Data Transfer Mode

After the card identification mode is set, it is then switched over to the transfer state where it waits for

either a write or read command. This section provides brief information about four different data transfer

modes:

• Block write

• Block read

• Stream write and read

4.3.1 Block Write

Blocks of data are written by sending data from the host to the MMC/SD card. Writing occurs during the

data transfer mode. Commands for writing are as follows:

• CMD24 WRITE_BLOCK

• CMD25 WRITE_MULTIPLE_BLOCK

• CMD26 PROGRAM_CID

• CMD27 PROGRAM_CSD

• CMD42 LOCK_UNLOCK

• CMD56 GEN_CMD

After a write command is implemented, the SD_CLK automatically stops and confirms whether the FIFO

is empty. When the FIFO is empty the SD_CLK starts and data is sent to the FIFO. The FIFO is 512 bytes

which is equivalent to the MMC/SD module the block size requirements. When the FIFO is full, the

SD_CLK stops automatically and sends the data to the MMC/SD card. The process of fetching another

Interfacing with the MMC/SD Module

Setup and Use of the Multimedia Card/Secure Digital Host Controller Application Note, Rev. 0

Freescale Semiconductor 9

block of data then repeats. Figure 2 is a screenshot of both the SD_CLK and the SD_DAT [0] pins

running on the i.MX1 using DMA transfer.

Figure 2. SD_CLK (1) and SD_DAT [0] (2) Multiple Block Write

4.3.2 Block Read

Blocks of data are read by sending data from the MMC/SD card to the host. Reading the data in the

MMC/SD card occurs during the data transfer mode. Commands for reading data are as follows:

• CMD17 READ_SINGLE_BLOCK

• CMD18 READ_MULTIPLE_BLOCK

• CMD30 SEND_WRITE_PROT

• CMD56 GEN_CMD

• ACMD51 SEND_SCR

After a read command is implemented the SD_CLK starts automatically and the FIFO fills with data

from the MMC/SD card. After the FIFO is full the SD_CLK stops. During this point the data from the

FIFO automatically is loaded into memory (RAM). When all the data has been loaded into memory the

SD_CLK starts again to get the next block of data from the MMC/SD card. Figure 3 is a screenshot of

both the SD_CLK and SD_DAT [0] pins of the i.MX1 using DMA transfer.

Special Considerations

Setup and Use of the Multimedia Card/Secure Digital Host Controller Application Note, Rev. 0

10 Freescale Semiconductor

Figure 3. SD_CLK (1) and SD_DAT [0] (2) Multiple Block Read

Both screenshots were captured using a low driving strength. If the driving strength (DS_SLOW bits) is

set to the maximum drive strength, it causes overshoot on the SD_CLK signal.

4.3.3 Stream Write and Read

The Stream Mode is not supported in any of the three processors.

5 Special Considerations

The MMC/SD module varies in speed during the data transfer mode. Table 3 and Table 4 describe the

various speeds of the MMC/SD module on the i.MX1 and i.MXL processors. The i.MX21 is referenced

in [6].

Table 3. i.MX1 Frequency Range

Card Type Method Size (Block Size) Minimum Maximum

MMC Polling Single 4 MHz 20 MHz

MMC Polling Multiple 4 MHz 20 MHz

MMC DMA Single 4 MHz 20 MHz

MMC DMA Multiple 4 MHz 20 MHz

SD (1-Bit Mode) Polling Single 4 MHz 25 MHz

SD (4-Bit Mode) Polling Single 8 MHz 25 MHz

SD Polling Multiple – –

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