Other Signals; Unused I/Os And Features; Figure 18. Typical Layout For Vdd/Vss Pair - ST STM32F74 Series Getting Started

AN4661
6.5

Other signals

When designing an application, the EMC performance can be improved by closely studying:
•
Signals for which a temporary disturbance affects the running process permanently
(the case of interrupts and handshaking strobe signals, and not the case for LED
commands). For these signals, a surrounding ground trace, shorter lengths and the
absence of noisy and sensitive traces nearby (crosstalk effect) improve EMC
performance. For digital signals, the best possible electrical margin must be reached
for the two logical states and slow Schmitt triggers are recommended to eliminate
parasitic states.
•
Noisy signals (clock, etc.).
•
Sensitive signals (high impedance, etc.).
6.6

Unused I/Os and features

All microcontrollers are designed for a variety of applications and often a particular
application does not use 100% of the MCU resources. To increase EMC performance,
unused clocks, counters or I/Os, should not be left free, e.g. I/Os should be set to "0" or "1"
(pull-up or pull-down to the unused I/O pins.) and unused features should be "frozen" or
disabled.
Figure 18. Typical layout for V
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/V pair
DD SS
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