General
Review and verify the following for the custom
schematic design:
- Reviewed above "Common checklist for all sections" section of the
user's guide.
- Provision for series resistors for interface signals near to the
source.
- Parallel pull provision added for the processor or attached device IOs.
- Interface signals (data, direction control) connections.
- Required communication speed (Baud rate) versus supported baud rates.
- Required communication errors (%) versus calculated communication errors (%)
due to internal clock divider mismatch.
- Processor IO supply for IO group and the attached device IO supply
connection.
- Fail-safe operation of UART interface signals.
- External ESD protection when the interface signals are connected directly to
external inputs.
Schematic Review
Follow the below list for the custom
schematic design:
- Provision for series resistors (22Ω) near to source added for the interface
signals to control possible signal reflections or isolate for testing.
- Parallel pull (10kΩ or 47kΩ) provided for the interface signals that can
float (to prevent the attached device inputs from floating until driven by
the host).
- Pullup referenced to (powered by) the processor VDDSHVx for corresponding
UART instance and signals matches.
- Interface signals (data, direction control) connections including signal
polarity matching.
- Supply rails connected to the IO supply for IO group VDDSHVx referenced to
(powered by) UART peripherals and attached devices IO supply are connected
to the same power source and follow the ROC.
- Provision for parallel pull added for any of the processor or attached
device IOs that can float.
- UART 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 external interface signals are connected directly and are sourced
from a different supply with respect to the processor IO supply for IO
group.
- Applying an external input signal to the
processor UART inputs before processor supply ramps can cause voltage feed and
can affect the custom board functions.
- The recommendation is to
provision for external ESD protection for the interface signals when external
inputs are connected directly.
- In case UART interfaces are not
used, the recommendation is to provide provision for connecting the UART0,
MCU_UART0 or WKUP_UART0 for debug.