Example 4: Configuring clocks for maximum speed

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Example 4: Configuring clocks for maximum speed

4.1

Overview

This example shows how to configure the STM8A microcontroller to run at its highest or

second highest frequency using the external or internal clock sources (HSE or HSI

respectively).

Such configurations make the CPU run at the frequency provided by the CLK without any

prescaler or division factors.

This example is provided as CLK example 4 in the STM8 firmware library.

4.2

Hardware description

The STM8/128-EVAL evaluation board is used for this example. The main hardware

connections are shown in Figure 1.

4.3

Firmware description

The CLK registers are configured so that the CPU runs at exactly 24 MHz (HSE clock

frequency).

Pressing the ‘KEY’ button on the evaluation board makes the CPU run at 16 MHz (HSI clock

frequency).

This example can be used as a tutorial exercise or as starting point that can be easily

modified for use in different applications.