AN4661 datasheet(25/33 Pages) STMICROELECTRONICS

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AN4661

Recommendations

Figure 15. Typical layout for VDD/VSS pair

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.

AN4661 Datasheet(PDF) 25 Page - STMicroelectronics