General
Review and verify the following for
the custom schematic design:
- Above sections, including
relevant application notes and FAQ links.
- Pin attributes, signal
description, and electrical specifications.
- Electrical characteristics,
timing parameters, and any additional available information.
- MMC0 interface is compliant with
the JEDEC eMMC electrical standard v5.1 (JESD84-B51)
- AM62Lx processor family implements a soft PHY.
The pulls required for DAT0, clock, and control signals are recommended to be
implemented externally.
- Include a series resistor (0Ω) on MMC0_CLK placed
as close to processor clock output pin as possible to minimize reflections.
MMC0_CLK is looped back internally on read transactions, and the series resistor
minimizes possible signal reflections, which cause false clock transitions. Use
0Ω initially and adjust as required to match the PCB trace impedance.
- Add pullups (10kΩ or 47kΩ) for DAT0 and CMD
signals. Connect the pullup to the IO supply for IO group VDDSHV2 (IO supply for
MMC0 IO group). For DAT1-7 eMMC device is expected to have the pullups enabled
during reset. The eMMC host/PHY disables the eMMC device pullups and enables
processor internal pullups. Provision for external pullups is optional, or
delete the pullups.
- VDDSHV2 (1.8V or 3.3V) and the attached eMMC
device IO supply is recommended to be powered from the same power source.
- Add a pulldown (10kΩ) to the eMMC attached device
close to the clock input pin.
- For implementing eMMC device reset, use a 2-input
ANDing logic when the memory is used for boot. Connect RESETSTATz as one of the
input and processor IO as another input. Add a pullup for the processor IO input
near the AND gate input pin and an isolation resistor near to the processor IO
output. Alternatively, RESETSTATz is used as the reset source. When RESETSTATz
is used as the reset source, verify the IO voltage level compatibility with the
eMMC IO supply. Use a level shifter as required.
- When eMMC boot is not configured, the eMMC
attached device reset can be controlled by the processor IO. The recommendation
is to pulldown the reset of the eMMC memory device during board power
reset.
- Add additional decoupling capacitors for attached
memory device as required. Refer EVM schematics.
Schematic Review
Follow the below list for the custom
schematic design:
- Required bulk and decoupling capacitors are
provided for processor and attached device rails. Compare with the EVM
schematics
- Pull values 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 clock output pin
- Implementation of reset logic
including the IO level compatibility. Adding a capacitor at the reset input of
eMMC attached device is not recommended when RESETSTATz or processor IO is
connected directly to control the reset. A stand-alone reset connection to reset
the eMMC memory device is not recommended
- Supply rails connected follow the
ROC
Additional
- Connect an external pulldown on CLK, and external
pullups on CMD and DAT0 to prevent the eMMC device inputs from floating until
software initializes the host controller and processor IOs associated with MMC0.
The eMMC standard mandates that eMMC devices have internal pullups enabled
during reset on DAT1-7, external pullups are not required for DAT1-7 signals.
Software turns on the respective internal DAT pullups when the bus width is
increased from 1-bit mode to 4-bit or 8-bit mode. External pulls are required
because the IOs associated with MMC0 are implemented with standard dual-voltage
LVCMOS IO cells with the capability of multiplexing additional signal functions
to the respective device pins. MMC0 IOs buffers are disabled during reset
because the interface connected to MMC0 pins is unknown.
- Verify eMMC_RSTn reset input is enabled in the
eMMC device (eMMC non-volatile configuration space) for the reset logic to be
functional. The GPIO reset option enables software to reset the attached device
(eMMC, OSPI, SD card or EPHY) without resetting the entire processor in cases
where the peripheral becomes unresponsive. Replace the GPIO option and use the
reset output, either warm or cold. Software forces a warm reset if the
peripheral becomes unresponsive. However, using warm reset resets the entire
device, rather than trying to recover the specific peripheral without resetting
the entire device. When RESETSTATz is used to reset the attached device, verify
the IO voltage level of the attached device matches the RESETSTATz IO voltage
level. A level translator is recommended to match the IO voltage level.
Alternatively, use a resistor divider and select an optimum impedance value. A
slow rise or fall time of the eMMC reset input causes too much delay. Low reset
input causes the processor to source too much steady-state current during normal
operation.
- ANDing logic additionally performs IO level
translation. Verify the reset IO level compatibility before optimizing the reset
ANDing logic. IO level mismatch can cause supply leakage and affect processor
operation
- Pulldown is selected for eMMC, SD
card or other peripherals since there are cases where the clock is stopped or
paused in a low logic state and the pulldown option is consistent with the logic
state.