Starting STM8 Microcontrollers

STM8S003K3 Discovery

Independent Watchdog (IWDG)

The IWDG is just the ordinary watchdog timer we usually find in any modern micro. The purpose of this timer is to recover a micro from an unanticipated event that may result in unresponsive or erratic behaviour. As the name suggests, this timer does not share anything with any other internal hardware peripheral and is clocked by LSI (128kHz) only. Thus, it is invulnerable to main clock (HSE or HSI) failure.

Block Diagram

Clock Diagram

The IWDG works by decrementing a counter, counting time in the process. When the counter hits zero, a reset is issued. Usually we would want that this reset never occurs and so the counter is periodically updated in the application firmware. If for some reason, the counter is not refreshed, a reset will occur, recovering the MCU from a disastrous situation.

Configuring the IWDG is very easy with SPL. There are certain steps to follow but SPL manages them well internally. All we’ll need is to configure the IWDG and reload it periodically before time runs out.

The formula required to calculate timeout is given below:

Formula

Typical values of timeout are as shown below:

Typical Values

 

Hardware Connection

CubeMX

Code Example

#include "STM8S.h"
 
 
void clock_setup(void);
void GPIO_setup(void);
void IWDG_setup(void);
 
 
void main(void)
{
    unsigned int t = 0;
                
    clock_setup();
    GPIO_setup();
                                
    GPIO_WriteLow(GPIOD, GPIO_PIN_0);
    for(t = 0; t < 60000; t++);
                
    IWDG_setup();
 
    while(TRUE)
    {
        GPIO_WriteReverse(GPIOD, GPIO_PIN_0);
        for(t = 0; t < 1000; t++)
        {
             if(GPIO_ReadInputPin(GPIOB, GPIO_PIN_7) == FALSE)
             {
                  IWDG_WriteAccessCmd(IWDG_WriteAccess_Enable);
                  IWDG_ReloadCounter();
                  IWDG_WriteAccessCmd(IWDG_WriteAccess_Disable);
             }
        }
     };
}
 
 
void clock_setup(void)
{
     CLK_DeInit();
                
     CLK_HSECmd(DISABLE);
     CLK_LSICmd(ENABLE);
     while(CLK_GetFlagStatus(CLK_FLAG_LSIRDY) == FALSE);
     CLK_HSICmd(ENABLE);
     while(CLK_GetFlagStatus(CLK_FLAG_HSIRDY) == FALSE);
                
     CLK_ClockSwitchCmd(ENABLE);
     CLK_HSIPrescalerConfig(CLK_PRESCALER_HSIDIV8);
     CLK_SYSCLKConfig(CLK_PRESCALER_CPUDIV4);
                
     CLK_ClockSwitchConfig(CLK_SWITCHMODE_AUTO, CLK_SOURCE_HSI, 
     DISABLE, CLK_CURRENTCLOCKSTATE_ENABLE);
                
     CLK_PeripheralClockConfig(CLK_PERIPHERAL_SPI, DISABLE);
     CLK_PeripheralClockConfig(CLK_PERIPHERAL_I2C, DISABLE);
     CLK_PeripheralClockConfig(CLK_PERIPHERAL_ADC, DISABLE);
     CLK_PeripheralClockConfig(CLK_PERIPHERAL_AWU, DISABLE);
     CLK_PeripheralClockConfig(CLK_PERIPHERAL_UART1, DISABLE);
     CLK_PeripheralClockConfig(CLK_PERIPHERAL_TIMER1, DISABLE);
     CLK_PeripheralClockConfig(CLK_PERIPHERAL_TIMER2, DISABLE);
     CLK_PeripheralClockConfig(CLK_PERIPHERAL_TIMER4, DISABLE);
}
 
 
void GPIO_setup(void)
{
     GPIO_DeInit(GPIOB);
     GPIO_DeInit(GPIOD);
 
     GPIO_Init(GPIOB, GPIO_PIN_7, GPIO_MODE_IN_PU_NO_IT);
     GPIO_Init(GPIOD, GPIO_PIN_0, GPIO_MODE_OUT_PP_LOW_FAST);
}
 
 
void IWDG_setup(void)
{
     IWDG_Enable();
     IWDG_WriteAccessCmd(IWDG_WriteAccess_Enable);
     IWDG_SetPrescaler(IWDG_Prescaler_128);
     IWDG_SetReload(0x99);
     IWDG_WriteAccessCmd(IWDG_WriteAccess_Disable);
}

 

Explanation

In this example, we need not to look at peripheral and CPU clock as IWDG is not dependent on them. Still we can see that the CPU is running at 500 kHz speed while the peripherals at 2 MHz speed.

CLK_HSIPrescalerConfig(CLK_PRESCALER_HSIDIV8);
CLK_SYSCLKConfig(CLK_PRESCALER_CPUDIV4);

To setup the IWDG, we need to enable it first and then apply Write Access Protection key (0x55). We just need to set the prescaler and the counter value. The down counter will start from this value and count down to zero unless refreshed. In this example, the prescaler is set to 128 and reload value is set to 153 (0x99). Thus, with these we get a timeout of approximately 300ms. After entering these values we must prevent accidental changes in the firmware and so to do so the write access must be disabled.

void IWDG_setup(void)
{
    IWDG_Enable();
    IWDG_WriteAccessCmd(IWDG_WriteAccess_Enable);
    IWDG_SetPrescaler(IWDG_Prescaler_128);
    IWDG_SetReload(0x99);
    IWDG_WriteAccessCmd(IWDG_WriteAccess_Disable);
}

Disco board’s user button and LED are used for the demo. At the very beginning, the LED is lit for some time before the IWDG is configured, indicating the start of the firmware. In the main loop, the LED is toggled with some delay arranged by a for loop. Inside the loop, the button’s state is polled. If the button is kept pressed it will always be in logic low state, reloading the IWDG counter. If its state changes to logic high and 300ms passes out, a reset is triggered.

GPIO_WriteReverse(GPIOD, GPIO_PIN_0);
for(t = 0; t < 1000; t++)
{
     if(GPIO_ReadInputPin(GPIOB, GPIO_PIN_7) == FALSE)
     {
          IWDG_WriteAccessCmd(IWDG_WriteAccess_Enable);
          IWDG_ReloadCounter();
          IWDG_WriteAccessCmd(IWDG_WriteAccess_Disable);
     }
}

Note it is possible to calibrate LSI. It is however rarely needed.

 

Demo

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50 comments

  • Thanks for this article..
    I am looking for microsd card interface with STM8s discovery board. can you please provide the tutorial for microsd card?

  • In relation to disabling unused peripheral clocks as suggested by you:

    I found the following list of peripherals in the STM8S105 Discovery Board: Advanced control timer (TIM1), General-purpose timers (TIM2 and TIM3), Basic timer (TIM4), SPI, I2C, UART2, Window WDG, Independent WDG, ADC1,
    AWU timer, Beeper.

    Is this all?

    I could not find the clock peripheral configuration function for Window WDG, Independent WDG, Beeper in the Standard Peripheral Library.
    Is it not required?

    P.S. I am new to MCU programming with a little experience on Arduino. So please forgive me if the question is foolish.

    • 1. STM8S003K3 Discovery – the one I use for the blog is different from STM8S105…. They have different peripherals and so there will be differences in peripheral clocks…. Please check the device datasheet/STM8CubeMX for available hardware….

      2. WWDG and IWDG are set in option bytes and they don’t use peripheral/CPU clock…. Their oscillator is separate…. Due to these they don’t have clock configurations like other peripherals….

      P.S: No question is a noob question…. every question is allowed no matter how silly it may look….

  • Hi please someone tel me where can i find stm8s_delay.h and stm8s_delay.c
    Thanks

  • Hi , please someone tel me . Where can i find stm8s_delay.h and stm8s_delay.c
    Thanks ..

  • i am using stms003f3p6 controller..i have done as u told exactly but tim1 input capture is not displaying any value …according to your article it should display 10…i dont have any errors everything is fine…pulse on tim2 is ok ..it is coming as u said…but capture not working..please help me …thank you…

  • Hi Sir,
    i have just follwed your instruction provied in yout tutorial in main.c

    #include “stm8s.h”

    main()
    {
    while (1);
    }

    This error comes, can you please check why this error come, i am new and learn the controller programming.

    main.c:
    The command: “cxstm8 -i”d:\other datasheet\new folder\lib\stm8s_stdperiph_lib\libraries\stm8s_stdperiph_driver\inc” +debug -pxp -no -l +mods0 -pp -i”C:\Program Files (x86)\COSMIC\FSE_Compilers\CXSTM8\Hstm8″ -clDebug\ -coDebug\ main.c ” has failed, the returned value is: 1
    exit code=1.

    main.o – 2 error(s), 0 warning(s)

    Thanks,

  • Hi there, i solve the previous ADC problem. Anyway, u make some good tutorial on stm8 chips. Nice work

    • What was causing that issue? How did you solve it?

      • because i put all these

        ADC_DeInit(ADC1);
        ADC_SamplingTimeConfig(ADC1, ADC_Group_SlowChannels, ADC_SamplingTime_4Cycles);
        ADC_SchmittTriggerConfig(ADC1, ADC_Channel_7, DISABLE);
        ADC_ChannelCmd(ADC1, ADC_Channel_7, ENABLE);
        ADC_Init(ADC1, ADC_ConversionMode_Continuous, ADC_Resolution_12Bit, ADC_Prescaler_1);
        ADC_Cmd(ADC1, ENABLE);
        ADC_ExternalTrigConfig(ADC1, ADC_ExtEventSelection_None, ADC_ExtTRGSensitivity_All);

        in ‘while(1)’. It keeps looping.

        Once i put it before ‘while (1)’, it becomes normal.

  • Hi there, thanks for sharing. I learn alot thru your example, but I have encounter a problem with adc. Im currently using stm8l151k4t6. I wanna use the pin D7 as to read the voltage from my battery and monitor it (display on LCD). Can u please check where it goes wrong on my code?

    ADC_DeInit(ADC1);
    ADC_SamplingTimeConfig(ADC1, ADC_Group_SlowChannels, ADC_SamplingTime_4Cycles);
    ADC_SchmittTriggerConfig(ADC1, ADC_Channel_7, DISABLE);
    ADC_ChannelCmd(ADC1, ADC_Channel_7, ENABLE);
    ADC_Init(ADC1, ADC_ConversionMode_Continuous, ADC_Resolution_12Bit, ADC_Prescaler_1);
    ADC_Cmd(ADC1, ENABLE);
    ADC_ExternalTrigConfig(ADC1, ADC_ExtEventSelection_None, ADC_ExtTRGSensitivity_All);
    ADC_SoftwareStartConv(ADC1);
    while(!ADC_GetFlagStatus(ADC1, ADC_FLAG_EOC));
    battery = ADC_GetConversionValue(ADC1);

  • hi shawon great tutorials it would be nice too if you covered the coide compiler for arm it’s a good free compiler

  • hi shawon thanks for your response and support it turns out that my problem was a license issue I stupidly thought i use one license on multiple pc’s I used the license for a particular computer for mine that’s why I’ve been having compilation issues you have to use the license file stm8 sends you that is generated by your own pc else it won’t compile it’ll jus kip throwing you errors

  • It seems that you didn’t follow my instructions completely…. I found some issues:

    1. You have included header and source files of ADC2, CAN, UART2, etc which are unavailable in STM8S103…. Add only files for the peripherals available in your target MCU…. Exclude the rest….

    2. You have not included stm8s_delay header and source files…. Either disable it from stm8s_conf.h header file if you are not going to use it or add both the header and the source files for it in your project….

    Resolve these and you are good to go….

    Thanks….

  • I haven’t compiled any of the examples yet I just tried to compile the main source file just for test purpose n it just keeps showing me the same errors

  • yes the comic compiler was installed properly i even received a license file from my mail with the instructions to copy the license file to the license folder in the install directory if you fail to do this it will keep popping up for you to put in the license file. iincluded all the source files and header files as instructed i am working with the cheap stm8s103f i uncommented the stm8s103f in the stm8.h header file as you instructed and just to compile the main file it just throws me errors

  • no I just followed your instructions I just compiled it after setup i did not write any code yet just compiled the default main file

    • Need more details….

      1. The version of STVD and Cosmic
      2. Which example is giving this issue?
      3. The chip you are using if it other than STM8S003
      4. Have you tried to compile something else other than my examples?
      5. Are the paths to libraries and other folders properly added?
      6. Is the Cosmic compiler registered properly?

  • it throws this line The command: “cxstm8 -iinc +debug -pxp -no -l +mods0 -pp -i”C:\Program Files (x86)\COSMIC\FSE_Compilers\Hstm8″ -clDebug\ -coDebug\ main.c ” has failed, the returned value is: 1
    exit code=1.

  • hi I’m having compilation issues when I compile it just throws me error about comic compiler located in the program file ialso excluded unwanted header files but my problems still weren’t solved

  • hi thanks for the tutorials but i am having compiler error issues even when I remove unnecessary header files it say comic compiler error

  • I am new to STM8S003k3 Discovery board.I have done UART communication using STM standard peripheral library example. Now I want to define any other GPIO pin for UART communication. Is it possible to use d0 and d1 pin for the UART communication? If yes, then please let me know how?

  • thank you very much for this article!

  • Thank you for your time and effort.

  • Good job bro

  • Thank you for this exceptionally comprehensive article, much appreciated

    Rando!

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