General
Review and verify the following for the custom
schematic design:
- Reviewed above "Common checklist for all sections" section of the
user's guide.
- There are no specific guidelines about implementation of pulls (CLK, DATA,
CMD, SDCD, SDWP) for embedded SDIO (providing or not providing pulls
internal to the interfaced device). Custom board designer implementing an
embedded SDIO device is responsible to determine the supported pulls on the
SDIO device and apply appropriate external pulls on the custom board
design.
- Implementation of series resistor and pulldown for MMC2_CLK
- MMC2 CLK, CMD, and DAT[3:0] signals interfaces, IO supply for IO group
supply connection
- Implementation of MMC2 SDCD and SDWP signals connection
- Implementation of attached device reset
Schematic Review
Follow the list below for the custom schematic
design:
- Required bulk and decoupling capacitors are provided for the supply rails.
The recommendation is to follow the processor-specific SK implementation for
bulk and decoupling capacitors when recommendations are not available.
- The MMC2 CLK, CMD, and DAT[3:0] signals interfaces are implemented using
SDIO buffers referenced to (powered by) IO supply for IO group VDDSHV6 (SDIO
buffer type IOs support dynamic voltage switching 3.3V or 1.8V to support
UHS-I SD card).
- For embedded SDIO application, the recommendation is to power IO supply for
IO group from the same fixed 1.8V or 3.3V power source that is used to power
the IOs of the attached device (Example: Wi-Fi module).
- MMC2 SDCD and SDWP signals
are implemented using LVCMOS buffers referenced to (powered by) IO supply
for IO group VDDSHV6 or VDDSHV0 (IOSET configuration), which operate at
fixed 1.8V or 3.3V. For SDIO use case VDDSHV6 can be used since the IO
supply is not switched. Use of SDCD and SDWP is use case dependent and there
are no specific recommendations.
- Series resistor (0Ω) for MMC2_CLK is placed close to processor clock output
pin to control possible signal reflections (which can cause false clock
transitions). A pulldown (10KΩ) is placed for MMC2_CLK near to the attached
device clock input to hold the clock input in a low state (there are cases
where the clock is stopped or paused in a low logic state and the pulldown
option is consistent with this logic state). The recommendation is to verify
processor or attached device internal pulls are not configured when external
pulls are used.
- Pull values used for the data, command and clock signals. The recommendation
is to follow the attached device recommendations or compare the
implementation with the SK schematic implementation. When no recommendations
are available for SDIO pulls, as good design practice, a 47kΩ pullup is
recommended for the pullup value (to be within the SD card specification
when internal pulls are enabled unexpectedly). With 47kΩ, the resulting pull
resistance (47kΩ external pullup in parallel to the internal pulldown) value
is still within the specified range. The recommendation is to verify
processor or attached device internal pulls are not configured when external
pulls are used.
- Supply rails connected to processor IO supply for IO group VDDSHVx (VDDSHV6
when used for SDIO or VDDSHV0 when IO set is configured) and attached device
IO supply follow the ROC.
- Processor IO can be used to implement the attached device reset. A pulldown
is recommended to hold the attached device in reset condition until the host
initializes the SDIO interface.
Additional
- Processor IO buffers are (TX
(Output) and RX (Input) are disabled during and after reset and internal pulls
(pullup and pulldown)) turned off during reset and after reset. An external
pullup is recommended for any of the processor or attached device IOs that can
float (to prevent the attached device inputs from floating until driven by the
host). Pullups are recommended on all data and command signals.
- The recommendation is to verify if the required external ESD protections have
been provided for the interface signals in case the signals are connected over
an add-on card.
- When using MMC1 for embedded SDIO interface, software changes are required since
the SK only implements the SDIO interface on MMC2. Custom board designers are
responsible for testing the performance.
- The processor IOs buffers (for MMCx signals) are off during reset and after
reset and are not enabled until the board has booted and the software
configures. To prevent floating inputs, the recommendation is to use external
pulls on the signals connected to the inputs of attached devices that can float.
To prevent floating inputs, use external pulls on any signals connected to the
inputs of attached devices that can float.