STM8S/A Standard Peripherals Firmware Library: CSS (Clock security system) capability

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  * @file    CLK/CLK_ClockSecuritySystem/readme.txt
  * @author  MCD Application Team
  * @version V2.2.0
  * @date    30-September-2014
  * @brief   This file contains the main function for Clock Security System example.
  ******************************************************************************
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  * Licensed under MCD-ST Liberty SW License Agreement V2, (the "License");
  * You may not use this file except in compliance with the License.
  * You may obtain a copy of the License at:
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  *        http://www.st.com/software_license_agreement_liberty_v2
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  * Unless required by applicable law or agreed to in writing, software 
  * distributed under the License is distributed on an "AS IS" BASIS, 
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
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  ******************************************************************************
  

Example description

This example demonstrates the CSS (Clock Security System) capability. The MCU clock system is configured as follows:

• HSI Prescaler = CLK_PRESCALER_HSIDIV8;
• Switch Mode = CLK_SWITCHMODE_AUTO
• New Clock = CLK_SOURCE_HSE;
• Current Clock State = CLK_CURRENTCLOCKSTATE_DISABLE;
• CSS = ENABLE

• When detecting the change of clock from HSE to HSI/8 (auxilary), LEDs blinking frequency becomes slower.

Directory contents

• CLK\CLK_ClockSecuritySystem\main.c Main file containing the "main" function
• CLK\CLK_ClockSecuritySystem\stm8s_conf.h Library Configuration file
• CLK\CLK_ClockSecuritySystem\stm8s_it.c Interrupt routines source
• CLK\CLK_ClockSecuritySystem\stm8s_it.h Interrupt routines declaration

Hardware and Software environment

• This example runs on STM8S and STM8A High density, Medium density and Low density devices.

• This example has been tested with STMicroelectronics STM8/128-EVAL evaluation board and can be easily tailored to any other development board.

• STM8/128-EVAL Set-up
  • LD1..LD4

How to use it ?

In order to make the program work, you must do the following :

• Copy all source files from this example folder to the template folder under Project
• Open your preferred toolchain
• Rebuild all files and load your image into target memory
• Run the example
• Observe the initial device frequency setting (HSE) on LED1, 2, 3, 4 of the Evaluation board (fast blinking frequency).
• Disconnect the crystal. The system clock will then switch to HSI backup clock as the CSS is enabled.
• The CPU is still processing operations but the frequency has changed to HSI/8 (CSS default clock): LED1, 2, 3, 4 are toggling at another frequency (Slower).
• The clock switching can be monitored by putting a scope on PE0 (CCO pin).

Hint

• Before using the HSE clock make sure that the "Flash_Wait_States" is set to 1.
  • with STVD (menu: Debug Instrument -> MCU configuration -> Options -> Flash_Wait_States: 1)
  • with RIDE (edit the "STM8_OB.asm" file to configure OPT7 & NOPT7 option bytes)
  • with EWSTM8 (menu: ST-LINK -> Option bytes ->Flash_Wait_States: 1)

Note:

• High-Density STM8A devices are the STM8AF52xx STM8AF6269/8x/Ax, STM8AF51xx, and STM8AF6169/7x/8x/9x/Ax microcontrollers where the Flash memory density ranges between 32 to 128 Kbytes
• Medium-Density STM8A devices are the STM8AF622x/4x, STM8AF6266/68, STM8AF612x/4x, and STM8AF6166/68 microcontrollers where the Flash memory density ranges between 8 to 32 Kbytes
• High-Density STM8S devices are the STM8S207xx, STM8S007 and STM8S208xx microcontrollers where the Flash memory density ranges between 32 to 128 Kbytes.
• Medium-Density STM8S devices are the STM8S105x and STM8S005 microcontrollers where the Flash memory density ranges between 16 to 32-Kbytes.
• Low-Density STM8S devices are the STM8S103xx, STM8S003 and STM8S903xx microcontrollers where the Flash density is 8 Kbytes.

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