AN3029 Datasheet, PDF (18/42 Pages) STMicroelectronics – Getting started with STM8L and STM8AL

Recommendations
AN3029
6.5
Other signals
When designing an application, the following areas should be closely studied to improve
EMC performances:
• 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 increases EMC performances, 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 for eliminating parasitic states.
6.6
Unused I/Os and features
Microcontrollers are designed for a variety of applications, where often a particular
application does not use 100 % of the microcontroller resources.
To avoid unnecessary power consumption (especially important for battery powered
applications) and also to improve EMC performance, unused clocks, counters, or I/Os,
should not be left free, I/Os should be forced externally (pull-up or pull-down to the unused
I/O pins), and unused functions should be ‘frozen’ or disabled.
Alternatively, unused I/Os can be programmed as push-pull ‘low’ to keep them at a defined
level without using external components. However in this case, the I/O is not driven during
the power up phase, until the I/O is configured. This can add a little extra power
consumption, and may be undesirable in very power sensitive applications.
6.7
User options
STM8L and STM8AL devices have user option features that can be used for remapping or
enabling/disabling an automatic reset or low speed watchdog. For more details, please refer
to the product datasheets.
6.8
Bootloader
STM8L05xx, STM8L15xxx, STM8L162xx, STM8AL31xx, and STM8AL3Lxx devices have a
bootloader embedded in a ROM memory. Through this firmware the device memory can be
re-programmed via:
• USART communication interface for medium density devices
• USART1, USART2, USART3, SPI1, and SPI2 communication interfaces for medium+
and high density devices.
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