General
Review and verify the following for
the custom schematic design:
- Above section 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, use a
resistor 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 DAT0-3 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 below list 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 board 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).