STM8AF51XX datasheet(17/100 Pages) STMICROELECTRONICS

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STM8AF61xx, STM8AF51xx

Product overview

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5.6.2

Internal 16 MHz RC oscillator

●

Default clock after reset 2 MHz (16 MHz/8)

●

Wake-up time: < 2 µs

User trimming

The register CLK_HSITRIMR with two trimming bits plus one additional bit for the sign permits

frequency tuning to a precision of 1% by the application program. The trimming step

granularity is 1.5 %.

The adjustment range covers all possible frequency variations versus supply voltage and

temperature. This trimming does not change the initial production setting.

5.6.3

Internal 128 kHz RC oscillator

The frequency of this clock is 128 kHz and it is independent from the main clock. It drives

the watchdog or the AWU wake-up timer.

In systems which do not need independent clock sources for the watchdog counters, the

128 kHz signal can be used as the system clock. This configuration has to be enabled by

setting an option byte (OPT3, LSI_EN).

5.6.4

Internal high-speed crystal oscillator

The internal high-speed crystal oscillator delivers the main clock in normal run mode. It

operates with quartz crystals and ceramic resonators.

●

Frequency range: 1 to 24 MHz

●

Crystal oscillation mode: Preferred fundamental

●

I/Os: Standard I/O pins multiplexed with OSCIN, OSCOUT

Optionally, an external clock signal can be injected into the OSCIN input pin.

5.6.5

External clock input

The external clock signal is applied to the OSCIN input pin of the crystal oscillator. The

frequency range is 0 to 24 MHz.

5.6.6

Clock security system (CSS)

The clock security system protects against a system stall in case of an external crystal clock

failure.

In case of a clock failure an interrupt is generated and the high speed internal clock (HSI) is

automatically selected with a frequency of 2 MHz (16 MHz/8). This function can be enabled

using the CSS register (CLK_CSSR).

The CSS operates by detecting when the external clock signal (crystal or external clock)

falls below 500 kHz. With active CSS this is the minimum operating frequency.

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