Verdin Carrier Board Design Guide
Preliminary
– Subject to Change
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2.8
SD/MMC/SDIO
The Verdin module form factor features one SDIO interface as "Always Compatible". The interface
provides 4 data bit which can be used for interfacing SD, SDIO, MMC and eMMC devices.
The SD cards support 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 changed from 3.3V to
1.8V. In the Verdin module definition, all GPIO capable interfaces are defined for 1.8V only. The
SDIO interface pins are an exception here. In order to be compliant with older SD cards, IO pins
need to start the communication at 3.3V voltage level. Therefore, the IO voltage rail of the SD card
signals is switchable between 1.8V and 3.3V voltage levels.
Some Verdin modules may feature additional SD interfaces as alternate functions of other
interfaces or on the "Module-specific" pins. Some of these additional SD interfaces may support
only 1.8V IO voltage levels. Since a detachable SD card needs to start the negotiation at 3.3V
voltage level, these ports can only be used for permanently attached devices like an eMMC
memory or a SDIO peripheral device.
Bus Speed Mode
Max. Clock
Frequency
Max. Bus Speed
Signal Voltage
Remarks
Default Speed
25 MHz
12.5 MB/s
3.3V
Default Speed
High Speed
50 MHz
25 MB/s
3.3V
High Speed
SDR12
25 MHz
12.5 MB/s
1.8V
UHS-I
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 19: SD Card Bus Speed Modes
2.8.1
SD/MMC/SDIO Signals
Verdin
Pin
Verdin
Signal Name
I/O
Type
Power
Rail
Description
80
SD_1_D0
I/O
CMOS
1.8V/3.3V
Data signals [3:0] - used for SD, MMC and SDIO interfaces; pull-
up resistors on the module
82
SD_1_D1
I/O
CMOS
1.8V/3.3V
70
SD_1_D2
I/O
CMOS
1.8V/3.3V
72
SD_1_D3
I/O
CMOS
1.8V/3.3V
74
SD_1_CMD
I/O
CMOS
1.8V/3.3V
Command signal; pull-up resistors on the module
78
SD_1_CLK
O
CMOS
1.8V/3.3V
Clock output
84
SD_1_CD#
I
OD
1.8V/3.3V
Card detect; pull-up resistors on the module
76
SD_1_PWR_EN
O
CMOS
1.8V/3.3V
Power Enable output
Table 20: 4bit SD/MMC/SDIO signals
The SD card bus signals (SD_1_D[0..3], SD_1_CMD, and SD_1_CLK) switch their input voltage
range all together. The card-detect (SD_1_CD#) and the power-enable (SD_1_PWR_EN) signals
may change their IO voltage together with the bus or remain at 1.8V. The behavior depends on
the Verdin module. The circuit on the carrier board needs to allow for having different IO voltages
on these pins, depending on the module and the card that is inserted.
2.8.2
Reference Schematics
Even though the SD card signals change their voltage between 1.8V and 3.3V, the card is always
powered with 3.3V. The signal pull-up resistors of the interface are located on the module or
inside the SoC. There are no pull-up resistors required on the carrier board. Therefore, there is no
need for a voltage rail on the carrier board that switches between 1.8V and 3.3V.
