AN4938 Rev 4 33/46
AN4938 Recommendations
45
Figure 17. Typical layout for V
DD
/V
SS
pair
7.5 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 the 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.).
7.6 Unused I/Os and features
All the microcontrollers are designed for a variety of applications and often a particular
application does not use 100% of the MCU resources. To increase the 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.
06Y9
9LDWR9''
9LDWR966
9''966
&DS
670+[[
&DS
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