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.
- Verify the IO voltage level connected based on the
buffer type implemented for the IOs used to
configure the interface
- Mapping of processor pin (ball number) to the required
functionality (peripheral, signal name) on custom
board (selected pin supports muxing (multiplex) the
IO for the required function) and naming of the
signal as per the processor data-sheet pin
attributes signal name column (when using standard
peripherals).
- Matching of the polarity of the peripheral data
interface signals between the processor and the
attached device (Example Mapping of Data, Clock or
similar connections)
- Emulated
open-drain output type I2C interface instances
(I2C0, I2C1, I2C2 (in case selected pins support
LVCMOS buffer type), I2C3, WKUP_I2C) Supported and
connection to multiple attached devices.
- Supported IO supply level for the I2C interfaces
(1.8V/3.3V or fixed 1.8V) vs Connected Voltage level
- Emulated
open-drain output buffer type I2C interface pin
configuration, I2C interface pullup recommendations
and connections.
- Connection of attached device address inputs.
- Emulated open-drain output type I2C interface exceptions
and connection recommendations (series resistor) for
fall time control
- Emulated
open-drain output type I2C interface fail-safe
operation
- Addition of required bulk and high frequency capacitors,
and value
- Emulated open-drain output type I2C interface connection
recommendations when interface is not used.
Schematic
Review
Follow the below list for
the custom schematic design:
- 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 EVM 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 or
VDDSx (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 or VDDSx 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
- LVCMOS type IO
buffer to emulate an open-drain output type IO 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.