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 or EVM
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 or 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 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 or EVM
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.