General
Review and verify the following for the custom
schematic design:
- The section
above, including relevant application notes and FAQ
links.
- Pin attributes,
signal description, and electrical specifications.
- Electrical
characteristics, timing parameters, and any additional
available information.
- Include a series
resistor (0Ω) on the MMC2_CLK, placed as close to processor
clock output pin as possible to dampen reflections. To
prevent signal reflections and false clock transitions, a
resistor can be required to eliminate possible signal
reflections on MMC2_CLK, which is looped back internally on
read transactions. Use 0Ω initially and adjust as required
to match the PCB trace impedance.
- The MMC2 CLK,
CMD, and DAT0 through DAT3 signal functions are implemented
with SDIO buffers on pins powered from VDDSHV6, which
operate at fixed 1.8V or 3.3V.
- The MMC2 SDCD and
SDWP signal functions are implemented with LVCMOS buffers on
pins powered from VDDSHV6 or VDDSHV0, which are operated at
fixed 1.8V or 3.3V.
- The SDIO buffers
are designed to support dynamic voltage change. When SDIO
interface is used, connecting a fixed IO voltage (1.8V or
3.3V) is recommended.
- Processor IO
buffers are off during reset. An external pullup is required
for any of the processor or attached device IOs that can
float. Pullups are needed on all data and command signals.
Verify internal pullups are not configured when (improves
noise immunity) external pullups are used. As a good design
practice, a 47kΩ pullup is recommended for the pullup value
to be within the SDIO specification when internal pulls are
enabled unexpectedly. With 47kΩ, the resulting pull
resistance is still within the specified.
- Attached device
reset implementation using processor IO. Verify the IO level
compatibility and the connection of required pull (polarity
is attached device dependent).
Schematic Review
Follow the list below for the custom schematic
design:
- Required bulk and decoupling
capacitors are provided. Compare with the SK schematics.
- Pull values used for the data,
command and clock signals. Compare with the relevant SK.
- Series resistor value and
placement on the clock output signal near to the processor.
- Implementation of reset
logic.
- Supply rails connected follow the
ROC and is a fixed supply.
Additional
- Verify required external ESD
protection are provided for the interface signals when connected over an add-on
card.
- Follow similar guidelines when
using MMC1. When using MMC1, software changes are required because the SK only
implements the SDIO interface on MMC2.
- There are no specific guidelines about SDIO
devices providing or not providing internal pulls. The board
designer implementing an embedded SDIO device must
understand what the SDIO device provides and apply the
appropriate external pull if not provided by the SDIO
device. Most of the processor IOs buffers are off during
reset and are not enabled until the system has booted and
the software configures. To prevent floating inputs, use
external pulls on any signals connected to the inputs of
attached devices.
- For embedded SDIO application, the recommendation
is to power IO supply rail from the same fixed 1.8V or 3.3V
power source that is used to power the IOs of the SDIO
attached device (an example is a Wi-Fi® module).