Figure 43: 8-bit MMC/SD Card Slot Reference Schematic
2.13.3 Unused SD/MMC/SDIO Interface Signal Termination
All unused SD interface signals can be left unconnected. If a complete SD/MMC/SDIO ports is
unused, the signal can be used as GPIO. Unused signals of a used port (for example the upper
four data bits of the 8-bit interface when used only in 4-bit mode), may be able to be used as
GPIO. Check the relevant Apalis module datasheet for more information.
2.14 I
2
C
The Apalis module standard features three I
2
C interfaces. The interface I2C1 is a general purpose
I
2
C while I2C2 is intended to be used with the DDC interface and I2C3 is intended to be used with
the camera interfaces. All I
2
C interfaces can also be used for general purpose.
The I
2
C as well as the DDC interfaces do not feature any pull-up resistors on the module. It is
required to add pull-up resistors to the data and clock lines on the carrier board. The pull-up
resistor value is typically between 1Ω and 10kΩ. A small pull-up resistor increases the power
consumption while a large resistor could lead to problems in the signal quality. The optimum size
of the resistor depends on the capacitive load on the I
2
C lines and the required bus speed.
2.14.1 I
2
C Signals
Table 24: I
2
C signals
2.14.2 Real-Team Clock (RTC) recommendation
The RTC on the module is not designed for ultra-low power consumption. Therefore, a standard
lithium coin cell battery can drain faster than allowed for certain designs. If a rechargeable RTC
battery is not a solution, it is recommended to use an external ultra-low power RTC IC on the
carrier board instead. In this case, add the external RTC to the I2C1 interface of the module and
leave the VCC_BACKUP pin unconnected.
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