AN2752 Rev 6 17/40
AN2752 Recommendations
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6.5 Other signals
When designing an application, the following areas have an impact on the EMC
performance:
• noisy signals (clock)
• sensitive signals (high impedance)
• signals for which a temporary disturbance permanently affects operation of the
application, for example, interrupts and handshaking strobe signals (but not LED
commands).
A surrounding V
SS
trace for such signals improves EMC performance, as does a shorter
length or absence of noisy and sensitive traces (crosstalk effect).
For digital signals, the best possible electrical margin must be reached for the two logical
states. Slow Schmitt triggers are recommended to eliminate parasitic states.
6.6 Unused I/Os and features
Microcontrollers are designed for a variety of applications, which fairly often do not use all
the available microcontroller resources.
To increase EMC performance it is advisable to let free unused clocks, counters, or I/Os. As
an example, set I/Os to ‘0’ or ‘1’ (pull-up or pull-down the unused I/O pins), and “freeze” or
disable unused functions.
Alternatively, unused I/Os can be programmed as push-pull ‘low’ in order to keep them at a
defined level, and not to use external components.
6.7 User options
STM8S and STM8AF devices have user option features that can be used for remapping or
enabling/disabling an automatic reset or low speed watchdog. For more details refer to the
product datasheet.
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