AN3029 datasheet(18/42 Pages) STMICROELECTRONICS

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AN3029

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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 VSS 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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