General
Review and verify the following for the custom schematic design:
- Reviewed above "Common checklist for all
sections" section of the user's guide.
- Timing and switching
characteristics, and any additional information available.
- I2C interface configuration, I2C interface pullup requirements and
connections.
- I2C pullup when interface is not used.
- I2C instances and connection to multiple attached devices.
- Terminations for attached device address inputs.
- Emulated open-drain output type I2C interface exceptions and connection
requirements.
Schematic Review
Follow the below list for the custom
schematic design:
- I2C0, I2C1, I2C2 and I2C3 I2C
interfaces are LVCMOS buffer type emulated open-drain output type IO.
- I2C interface configuration and recommended connections (including grouping
of the interface signals as per IOSET). I2C interface type and pullup
requirements.
- A pullup (4.7kΩ) is
recommended when IO is configured as I2C interface.
- The recommendation is to verify the pullup values used for the I2C
interfaces with the SK schematic implementation or calculate the pullup
value based on the load. A pullup (4.7kΩ, adjust after testing) is
recommended for the I2C interfaces.
- Pullup referenced to (powered by) the processor VDDSHVx (I2C pullup
connected to correct voltage).
- When I2C interface is not used, these IOs can be configured for alternate
functions and the pulls are dependent on the IO function.
- Supply rails connected to the IO supply for IO group VDDSHVx referenced to
(powered by) I2C peripherals and attached devices IO supply are sourced from
the same supply and follow the ROC.
- Processor supports multiple I2C instances. The recommendation is to verify
that there are no I2C address conflicts on any of the I2C interface. In case
additional I2C interfaces are required, an I2C switch can be used.
- Attached device address pin connected to IO supply through a resistor (>
1kΩ).
- Note the I2C exceptions in
the Timing and Switching Characteristics section of the
processor-specific data sheet for emulated open-drain output type I2C
interface. Series resistor (47Ω, adjust after testing) is recommended near
to the processor I2C interface signals to control fall time.
Additional
- I2C0, I2C1, I2C2, and I2C3 interfaces use
LVCMOS type IO buffer to emulate an open-drain
output type IO and are not fully compliant with
the I2C specification, in particular falling edges
are fast (< 2ns).
- The recommendation is to review the Timing
and switching characteristics, I2C
Exceptions section of the processor-specific
data sheet during the design stage.
- The I2C bus can only be operated as fast as
the slowest peripheral on the bus. If faster
operation is required, move the slow devices to
another I2C port.
- The recommendation is to not place more than
one set of pullup resistors on the I2C bus, the
pullups can result in excessive loading and
potential incorrect operation. Adjust the pullup
value based on the bus speed configured.
- The recommendation is to make sure IO supply
for IO group powering the processor I2C IOs
matches the supply voltage used for the pullup and
the attached I2C devices IO supply. Connecting the
pullups to proper supply level can prevent
incorrect I2C interface operation.
- I2C interfaces support clock stretching. The
recommendation is to adjust the pullup in case the
measured clock frequency does not match the
configured frequency due to the bus loading or
signal slew rate.
- Fail-safe interface support (emulated open-drain output type IOs are not
fail-safe, no external input is recommended to be applied recommended to be
applied before the processor IO supply ramps). The recommendation is to verify
fail-safe operation when connected to external interface signals. Applying an
external input signal to the processor I2C inputs before processor supply ramps
can cause voltage feed and can affect the custom board functions.