Functional Description
shows the MMC/SD/SDIO0 host controller connected to an MMC, SD, or SDIO card and its
related external connections. Note that MMC/SD/SDIO0 uses the same signals as MMC/SD/SDIO1 and 2
but adds MMC_POW.
The following MMC/SD/SDIO controller pins are used
•
MMC_CMD This pin is used for two-way communication between the connected card and the
MMC/SD/SDIO controller. The MMC/SD/SDIO controller transmits commands to the card and the
memory card drives responses to the commands on this pin.
•
MMC_DAT7-0 Depending on which type of card you are using, you may need to connect 1, 4, or 8
data lines. The number of DAT pins (the data bus width) is set by the Data Transfer Width (DTW) bit in
the MMC control register (SD_HCTL). For more information, see
, MULTIMEDIA_CARD
Registers.
•
MMC_CLK This pin provides the clock to the memory card from the MMC/SD controller.
•
MMC_POW Used for MMC/SD card's cards on/off power supply control. When high, denotes power-on
condition.
•
MMC_SDCD This input pin serves as the MMC/SD/SDIO carrier detect. This signal is received from a
mechanical switch on the slot.
•
MMC_SDWP This input pin is used for the SD/SDIO card's write protect. This signal is received from a
mechanical protect switch on the slot (system dependant). Applicable only for SD and SDIO cards that
have a mechanical sliding tablet on the side of the card.
Note: The MMC_CLK pin functions as an output but must be configured as an I/O to internally
loopback the clock to time the inputs.
provides a summary of these pins.
Table 18-7. MMC/SD/SDIO Controller Pins and Descriptions
Pin
Type
1-Bit Mode
4-Bit Mode
8-Bit Mode
Reset Value
MMC_CLK
(1)
O
Clock Line
Clock Line
Clock Line
High impedance
MMC_CMD
I/O
Command Line
Command Line
Command Line
High impedance
MMC_DAT0
I/O
Data Line 0
Data Line 0
Data Line 0
0
MMC_DAT1
I/O
(not used)
Data Line 1
Data Line 1
0
MMC_DAT2
I/O
(not used)
Data Line 2
Data Line 2
0
MMC_DAT3
I/O
(not used)
Data Line 3
Data Line 3
0
MMC_DAT4
I/O
(not used)
(not used)
Data Line 4
0
MMC_DAT5
I/O
(not used)
(not used)
Data Line 5
0
MMC_DAT6
I/O
(not used)
(not used)
Data Line 6
0
MMC_DAT7
I/O
(not used)
(not used)
Data Line 7
0
(1)
The MMC_CLK pin functions as an output but must be configured as an I/O to internally loopback the clock to time the inputs.
18.3.1.2 Protocol and Data Format
The bus protocol between the MMC/SD/SDIO host controller and the card is message-based. Each
message is represented by one of the following parts:
Command: A command starts an operation. The command is transferred serially from the
\MMC/SD/SDIO host controller to the card on the mmc_cmd line.
Response: A response is an answer to a command. The response is sent from the card to the
MMC/SD/SDIO host controller. It is transferred serially on the mmc_cmd line.
Data: Data are transferred from the MMC/SD/SDIO host controller to the card or from a card to the
MMC/SD/SDIO host controller using the DATA lines.
Busy: The mmc_dat0 signal is maintained low by the card as far as it is programming the data received.
3351
SPRUH73H – October 2011 – Revised April 2013
Multimedia Card (MMC)
Copyright © 2011–2013, Texas Instruments Incorporated