Atmel Xplained Evaluation Board AT32UC3A3-XPLD AT32UC3A3-XPLD Data Sheet

32072H–AVR32–10/2012

Figure 31-8. Mixing MultiMedia and SD Memory Cards with Two Slots

When the MCI is configured to operate with SD memory cards, the width of the data bus can be
selected in the SDCard /SDIO Bus Width field in the SDCR register (SDCR.SDCBUS). 

 for details.

In the case of multimedia cards, only the data line 0 is used. The other data lines can be used as
independent GPIOs. 

When more than one card (MMC or SD) is plugged to the device, it is strongly recommended to
connect each card’s clock to a dedicate MCI CLK pin of the device. Otherwise, Compliance to
specifications is not guaranteed.

After a power-on reset, the cards are initialized by a special message-based MultiMedia Card
bus protocol. Each message is represented by one of the following tokens:

• Command: a command is a token that starts an operation. A command is sent from the host 

either to a single card (addressed command) or to all connected cards (broadcast 
command). a command is transferred serially on the CMD line.

• Response: a response is a token which is sent from an addressed card or (synchronously) 

from all connected cards to the host as an answer to a previously received command. A 
response is transferred serially on the CMD line.

• Data: data can be transferred from the card to the host or vice versa. Data is transferred via 

the data line.

Card addressing is implemented using a session address assigned during the initialization
phase by the bus controller to all currently connected cards. Their unique CID number identifies
individual cards.

4

9

23

15

6

7

8

SDCARD

DATA[7:0]

CMD[0]

CLK

DATA[11:8]

CMD[1]

1 2 3 4 5 6

MMC1

7

910

1213 8

11

1 2 3 4 5 6

MMC2

7

910

1213 8

11

1 2 3 4 5 6

MMC3

7

910

1213 8

11

CLK