Toradex Apalis Series - SD;MMC;SDIO Signals

Apalis Carrier Board Design Guide
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The SD cards know different bus speed modes. The required signal voltage depends on the bus
speed mode. In UHS-I (Ultra High Speed), the signaling voltage need to be dropped from 3.3V to
1.8V. In the Apalis module definition, all GPIO capable interfaces including the SD/MMC/SDIO are
defined for 3.3V. Some Apalis modules might be capable to switch the voltages of the SD card
interface pins to a 1.8V, but it is not mandatory. Read the relevant datasheet of the Apalis module.
Even if the bus speed mode requires the signaling voltage of 1.8V, the supply of the card itself is
still 3.3V. Pay attention to the SD card signal pull-up resistors on the carrier board. If the 1.8V
mode is supported by the Apalis module, the voltage for the pull-up resistors also needs to be
switchable. Currently, all available Apalis modules allow removing the pull-up resistors on the
carrier board and using the internal ones only. It is the preferred solution. Even if the external pull-
up resistors are not mandatory, we recommend adding unassembled pull-up resistors to the 3.3V
rail in order for it to be compatible with the future modules.
Bus Speed Mode
Max. Clock Frequency
Max. Bus Speed
Signal Voltage
Default Speed
25 MHz
12.5 MB/s
3.3V
High Speed
50 MHz
25 MB/s
3.3V
SDR12
25 MHz
12.5 MB/s
1.8V
SDR25
50 MHz
25 MB/s
1.8V
DDR50
50 MHz
50 MB/s
1.8V
SDR50
100 MHz
50 MB/s
1.8V
SDR104
208 MHz
104 MB/s
1.8V
Table 21: SD Card Bus Speed Modes
2.13.1 SD/MMC/SDIO Signals
Apalis
Pin
Apalis
Signal Name
I/O
Type
Power
Rail
Description
160
MMC1_D0
I/O
CMOS
3.3V
Data signals [3:0] - used for SD, MMC and SDIO interfaces; add
external pull-up resistors
162
MMC1_D1
I/O
CMOS
3.3V
144
MMC1_D2
I/O
CMOS
3.3V
146
MMC1_D3
I/O
CMOS
3.3V
148
MMC1_D4
I/O
CMOS
3.3V
Data signals [7:0] - only needed for 8-bit MMC interface; add external
pull-up resistors; for 4bit MMC, SD and SDIO - leave this pins
unconnected
152
MMC1_D5
I/O
CMOS
3.3V
156
MMC1_D6
I/O
CMOS
3.3V
158
MMC1_D7
I/O
CMOS
3.3V
150
MMC1_CMD
I/O
CMOS
3.3V
Command signal - add external pull-up resistor
154
MMC1_CLK
O
CMOS
3.3V
Clock output
164
MMC1_CD#
I
CMOS
3.3V
Card detect, add pull-up resistor if card detect is used
Table 22: 8bit SD/MMC/SDIO signals