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 designers implementing an
embedded SDIO device are responsible for determining the supported pulls on
the SDIO device and apply appropriate external pulls on the custom board
design.
- Mapping of processor pin (ball number) to the required functionality
(peripheral, signal name) on custom board (selected pin supports muxing
(multiplex) the IO for the required function) and naming of the signal as
per the processor data-sheet pin attributes signal name column (when using
standard peripherals).
- Matching of the polarity of the peripheral data interface signals between
the processor and the attached device (Example Mapping of D0-D3 (data) of
processor to D0-D3 of attached device or similar connections)
- Implementation of series resistor and pulldown for MMC2_CLK
- Implementation of pullups for MMC2 CMD, and DAT [3:0] signals
- Dual-voltage IO supply for IO group supply connection (fixed voltage
connected)
- Implementation of MMC2 SDCD and SDWP signals connection
- Implementation of attached
device reset logic
- Addition of required bulk and high frequency capacitors, and value.
Schematic Review
Follow the list below for the custom
schematic design:
- The MMC2 CLK, CMD, and DAT[3:0] signals interfaces are implemented using
SDIO buffers referenced to (powered by) dual-voltage IO supply for IO group
VDDSHV4 (SDIO buffer type IOs support dynamic voltage switching 3.3V or 1.8V
to support UHS-I SD card).
- Required bulk and decoupling capacitors are provided for the supply rails.
The recommendation is to follow the processor-specific EVM implementation
for bulk and decoupling capacitors when recommendations are not available.
- For embedded SDIO application, the recommendation is to power dual-voltage
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) dual-voltage IO supply for IO group VDDSHV4 or VDDSHV1
(IOSET configuration), which operate at fixed 1.8V or 3.3V. For SDIO use
case VDDSHV4 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 for control of
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 EVM
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 resistance range specified in the relevant standards. The recommendation
is to verify processor or attached device internal pulls are not configured
when external pulls are used.
- Supply rails connected to processor dual-voltage IO supply for IO group
VDDSHVx (VDDSHV4 when used for SDIO or VDDSHV1 when IO set is configured)
and attached device IO supply follow the ROC.
- When processor IO is 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
- 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 EVM only implements the SDIO
interface on MMC2. Custom board designers are responsible for testing the
performance.
- Processor IO buffers (for MMCx
signals) are off during reset and after reset. The IO buffers are not enabled
until the board has booted and the software configures the IOs. To prevent
floating of processor IOs or the attached device inputs being driven by the
processor IOs the recommendation is to add external pulls on the signals
connected to the inputs of attached devices.