General
Review and verify the following for the custom
schematic design:
- Reviewed above "Common checklist for all sections" section of the
user's guide
- Interface configuration and connections
- Series resistor provision for clock output and placement
- Series resistors provision for the interface signals near to the source
- Connection of parallel pulls for clock, data and chip select
- External SPI Chip Selects connection
- Connection of IO supply for IO group and attached device IO supply.
- Interface performance and signal integrity
- Configuration of SPI data signals
- Fail-safe operation of interface signals
Schematic Review
Follow the below list for the custom schematic design:
- Interface configuration and
recommended connections (including IOSET).
- Series resistor 22Ω added to the clock output signal near to processor clock
output pin (used for retiming).
- Provision for series resistors added (optional) for the interface signals
(to isolate for testing or to control possible signal reflections).
- Pullup referenced to (powered by) the processor
VDDSHVx for corresponding MCSPI instance and signals.
- Processor VDDSHVx and the attached device IO
supply are sourced from the same supply.
- Supply rails connected to the IO supply for IO
group VDDSHVx referenced to (powered by) MCSPI peripherals and attached
devices IO supply follow the ROC.
- Pulldown (10kΩ) provision for MCSPI clock
(close to attached device clock input pin) to hold
the attached device in low state (there are cases
where the clock is stopped or paused in a low
logic state and the pulldown option is consistent
with this logic state) for all IOs configured for
MCSPI interfaces.
- Provide provision for external pullups for SPI Chip Select SPI0..2_CS0..3
(MCSPI 0..2) and MCU_SPI0..1_CS0..3 (MCU MCSPI 0..1) (close to attached
device). The recommendation is to add pulls to the processor and the
attached device signals (data interface - data in, data out) that can float
(to prevent the attached device inputs from floating until driven by the
host). Pullup values used (10kΩ or 47kΩ).
- Configuration of processor
SPIx data bits D0 and D1 bits (data direction) matches the attached device
and required pulls are added for signals that can float.
- Parallel pull added for the processor or attached IOs that can float.
- Interface performance (speed, data throughput, communication errors) and
signal integrity related concerns have been analyzed (simulated) when
connecting to multiple attached devices.
- MCSPI interface signals are not fail-safe. The recommendation is to apply
the inputs only after the processor supply ramps.
Additional
- The recommendation is to verify fail-safe operation when processor IOs are
directly connected to external interface signals or connector (through carrier
board or add-on board). Applying an external input signal to the processor MCSPI
inputs before processor supply ramps can cause voltage feed and can affect the
custom board functions.
- External ESD protection when the interface signals are connected directly to
external inputs.