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 minimize reflections. To prevent signal reflections and false clock transitions, use a series resistor to minimize 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 VDDSHV4, which operate at 1.8V or 3.3V.
- The MMC2 SDCD and SDWP signal functions are implemented with LVCMOS buffers on pins powered from VDDSHV4 or VDDSHV1, which are operated at fixed 1.8V or 3.3V.
- The SDIO buffers are designed to support dynamic voltage switching. 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 recommended for any of the processor or attached device IOs that can float.
Pullups are recommended 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 are 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 EVM schematics.
- Pull values used for the data, command and clock signals. Compare with the relevant EVM schematics.
- 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 EVM 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 is expected to 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 for IO group from the same fixed 1.8V or 3.3V power source that is used to power the IOs of the SDIO interface attached device (an example is a Wi-Fi module).