Starting STM8 Microcontrollers

STM8S003K3 Discovery

External Interrupt (EXTI)

External interrupt is an additional feature of GPIOs in input mode. It makes a micro to respond instantly to changes done on it GPIO input pin(s) by an external events/triggers, skipping other tasks. External interrupts are useful in many scenarios. For instance, an emergency button. Consider the case of a treadmill. You are running at a speed and suddenly you get an ache in one of your ankles. You’ll surely want to stop running immediately. Rather decreasing speed in small steps, you can hit the emergency button to quickly stop the treadmill. The emergency button will interrupt all other processes and immediately instruct the treadmill’s CPU to decrease speed faster than otherwise possible. Thus, it has high priority over other processes.

In most 8-bit micros, there are few external interrupt pins and very limited options are available for them but that’s not the case with STM’s micros. In STM8s, almost all GPIO pins have independent external interrupt capability with input Schmitt triggers. Additionally, there’s interrupt controller to set interrupt priority.



Hardware Connection


Code Example

We will do the same variable flash rate LED blinking example as in the GPIO example but this time with the DISCO board’s button in external interrupt mode. The code here needs special attention as now we will see how interrupts are configured and coded. This code is way different than anything I saw before. I’m saying so because you’ll need to follow certain steps unlike other compilers. In other compilers, all we do is create the interrupt function and tell the compiler the interrupt vector address. Same here too but too many steps involved.

Now check the interrupt vector table of STM8S003 below:

Vector Table

You’ll find this table not in the reference manual but in the device’s datasheet. This table varies with devices and so be sure of correct datasheet. The DISCO board’s button is connected to PB7 and so clearly, we will need IRQ4, i.e. EXTI1 or PORTB external interrupts. All external interrupts on GPIOB pin are masked in this vector address.

Please note that codes that use peripheral interrupts need stm8s_it.h and stm8s_it.c files. Therefore, add them if you are to use interrupts.


#include "stm8s.h"
bool state = FALSE;
void GPIO_setup(void);
void EXTI_setup(void);
void clock_setup(void);
void main(void)
         GPIO_WriteReverse(GPIOD, GPIO_PIN_0);
         if(state == TRUE)
    }while (TRUE);
void GPIO_setup(void)
void EXTI_setup(void)
void clock_setup(void)
    while(CLK_GetFlagStatus(CLK_FLAG_HSIRDY) == FALSE);
    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);



 *              Copyright (c) 2007 STMicroelectronics
#include "stm8s_it.h"
typedef void @far (*interrupt_handler_t)(void);
struct interrupt_vector 
    unsigned char interrupt_instruction;
    interrupt_handler_t interrupt_handler;
//@far @interrupt void NonHandledInterrupt (void)
                /* in order to detect unexpected events during development, 
                   it is recommended to set a breakpoint on the following instruction
//              return;
extern void _stext();     /* startup routine */
struct interrupt_vector const _vectab[] = {
                {0x82, (interrupt_handler_t)_stext}, /* reset */
                {0x82, NonHandledInterrupt}, /* trap  */
                {0x82, NonHandledInterrupt}, /* irq0  */
                {0x82, NonHandledInterrupt}, /* irq1  */
                {0x82, NonHandledInterrupt}, /* irq2  */
                {0x82, NonHandledInterrupt}, /* irq3  */
                {0x82, (interrupt_handler_t)EXTI1_IRQHandler}, /* irq4  */
                {0x82, NonHandledInterrupt}, /* irq5  */
                {0x82, NonHandledInterrupt}, /* irq6  */
                {0x82, NonHandledInterrupt}, /* irq7  */
                {0x82, NonHandledInterrupt}, /* irq8  */
                {0x82, NonHandledInterrupt}, /* irq9  */
                {0x82, NonHandledInterrupt}, /* irq10 */
                {0x82, NonHandledInterrupt}, /* irq11 */
                {0x82, NonHandledInterrupt}, /* irq12 */
                {0x82, NonHandledInterrupt}, /* irq13 */
                {0x82, NonHandledInterrupt}, /* irq14 */
                {0x82, NonHandledInterrupt}, /* irq15 */
                {0x82, NonHandledInterrupt}, /* irq16 */
                {0x82, NonHandledInterrupt}, /* irq17 */
                {0x82, NonHandledInterrupt}, /* irq18 */
                {0x82, NonHandledInterrupt}, /* irq19 */
                {0x82, NonHandledInterrupt}, /* irq20 */
                {0x82, NonHandledInterrupt}, /* irq21 */
                {0x82, NonHandledInterrupt}, /* irq22 */
                {0x82, NonHandledInterrupt}, /* irq23 */
                {0x82, NonHandledInterrupt}, /* irq24 */
                {0x82, NonHandledInterrupt}, /* irq25 */
                {0x82, NonHandledInterrupt}, /* irq26 */
                {0x82, NonHandledInterrupt}, /* irq27 */
                {0x82, NonHandledInterrupt}, /* irq28 */
                {0x82, NonHandledInterrupt}, /* irq29 */


Now check the top parts of the stm8s_it.h and stm8s_it.c files respectively.






These must be coded.



Most part of the code is same as previous codes and so I won’t be going through them again. However, there’s something new:

void EXTI_setup(void)

This function is where we are setting up the external interrupt. The first two lines deinitiate the interrupt controller and set priority while initiating it. It is not mandatory unless you want to set interrupt priority. Then we configure the external interrupt on PORTB pins. We also set the edge that will invoke an interrupt. Finally, we enable global interrupt. There goes the main.c file

Now it’s time to explain the stm8_interrupt_vector.c file. The top part of this file must include this line #include “stm8s_it.h”. It must also have the following section commented out:

//@far @interrupt void NonHandledInterrupt (void)
                /* in order to detect unexpected events during development, 
                   it is recommended to set a breakpoint on the following instruction
//              return;

We need to let our compiler know the name of the function that it should call when a particular interrupt is triggered. There are two parts for that. Firstly, the interrupt vector address and secondly the name of the function. This is reason for this line:

{0x82, (interrupt_handler_t)EXTI1_IRQHandler}, /* irq4  */

Lastly, the stm8s_it.h and stm8s_it.c files contain the prototype and the function that will execute the interrupt service routine (ISR). In our case, the ISR will change the logic state of the Boolean variable state. This will alter that flashing rate in the main loop.


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  • Hi
    I am using stm8s003f3 pin out board and with this code I am just testing output at micro controller pin 2 i.e. TX
    I am testing this using an oscilloscope.
    but not able to get any output
    Can you please help?


  • SSI_Electronics

    I have followed the code as per the explanation.
    but I’m getting garbage values on serial port.
    Can you suggest any debugging steps??
    Thanks in advanced.

    PS: Great tutorial. It’s helping me a lot.

    • 1. Check wiring for loose connections….
      2. Use a stable and noise-free power source like a battery-bank to power up the board…. Noise from PC port may cause unwanted issues….
      3. Use CP2102 or FT232-based USB-TTL converter…. Don’t use PL2303-based ones because most are clones or fakes….
      4. Use a short USB cable….
      5. Use external pull-up resistors for both TX and RX pins….
      6. Try with another board if these don’t solve the issue…. It should not behave as you are saying because the code has no issues….

  • santosh kharade

    Serial receiving program is not working

  • Hello sir
    Do you tell me how generate pwm in pin no. B5 & B5
    in Stm8 board

    • Which STM8 chip? Because different chips have different pin mapping and sometimes there are alternative pins for such purposes…. Check with STM8CubeMX if that pin is available for that purpose….

  • Santosh Kharade

    i have done code for multi channel adc but its not working ????
    when i use single channel adc its working properly…………

  • Hello guys
    here i’m again for ask your help. I wrote a very easy program but when i try to send to stm8 the light programmer give me this error :

    >Erase not feasible
    Error: Device not recognized !

    some idea ?
    Thank you

  • First thank you so much for this wonderful tutorial, i’m new with STM8 i follow all you steps but i still have a problem and here i’m please can you help me this is the error message.
    Thank you

    ———– Project test_prov – STM8 Cosmic – Configuration Debug ————-

    Compiling main.c…
    cxstm8 -i..\..\en.stsw-stm8069\stm8s_stdperiph_lib\project\stm8s_stdperiph_template -igpio -iinc +debug -pxp -no -l +mods0 -pp -i”C:\Program Files (x86)\COSMIC\FSE_Compilers\CXSTM8\Hstm8″ -clDebug\ -coDebug\ main.c
    #error cpstm8 gpio\inc\stm8s.h:74 “Please select first the target STM8S/A device used in your application (in stm8s.h file)”
    The command: “cxstm8 -i..\..\en.stsw-stm8069\stm8s_stdperiph_lib\project\stm8s_stdperiph_template -igpio -iinc +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.

    test_prov.elf – 2 error(s), 0 warning(s)

  • Hi Shawon ,
    Excellent article on stms8.
    within 3 days i was able to understand STMS8 very clearly.
    can you send me delay library files please.
    i tried to create my own without any success.
    warm regards

  • hi sir now also getting problem in compilation time …..’

    so plz can u send me the soft copy of software wat properly working at u…??

    my emain id…

    • I’m using the same software you are using – the latest one out there…. and so someone sending it has no meaning…. I suggest that you uninstall it and give it fresh retry, following all the steps carefully…. No one can help you with licensing issue unless to do it correctly….

  • hi geting poroblem while click on programmer ten my softare automatically close tab

  • hi sir…

    i getting problem for license configured……………. at compile time getting error like that…………. plz help out

    #error cpstm8 C:\Program Files (x86)\COSMIC\FSE_Compilers\CXSTM8\HSTM8\mods0.h:1 FlexLM Cannot find license file.
    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.

    alpha_lcd.elf – 3 error(s), 0 warning(s)

  • helo…we hav stm8svl discovery..i need embedded c program for the glowing of led,connecting ir receiver and also powersupply…for connecting these things i need code can u please guide me

  • 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

  • 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 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”

    while (1);

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

    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)


  • 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_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_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);
    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….


  • 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


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