© National Instruments
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NI sbRIO-9651 System on Module Carrier Board Design Guide
Reference Schematic Design Considerations
Table 1-13 lists design considerations for the schematic shown in Figure 1-5.
Table 1-13.
SD Reference Schematic Design Considerations
Consideration
Notes
SD_CLK,
SD_CMD, and
SD_D0 through
SD_D3
• You can route these signals directly from the sbRIO-9651 SOM to the
SD connector.
• Each of these signals requires series termination near its driver. The
sbRIO-9651 SOM provides series termination near the Xilinx Zynq
SoC to prevent overshoot on the SD card when the sbRIO-9651 SOM
drives these signals. The bi-directional signals also require series
termination at the SD converter.
• Use series termination at the SD connector for the SD_CMD and
SD_D0 through SD_D3 signals to prevent overshoot on the
sbRIO-9651 SOM when the SD card drives these signals.
SD_CD#
• The SD_CD# signal is connected to the mechanical card-detect switch
in the SD connector.
• When a card is inserted, the card-detect pin on the SD connector is
shorted to ground.
• Because this is a mechanical switch with low output impedance, you
must place a series termination resistor (R216) at the SD connector.
• You must have a card-detect switch to properly support hot-swapping
cards. If you do not need to support hot-swapping cards, you can use
an SD connector without a card-detect switch. In this case, tie the
SD_CD# signal to ground so that the sbRIO-9651 SOM attempts to
initialize a card on boot.