Continuing the STM8 Expedition

One Pulse Mode (OPM)

One Pulse Mode (OPM) is an additional feature of STM8 timers. It is like a monostable multivibrator or a one-shot timer that can be used to generate a pulse of fixed width after a defined amount of delay. It has several uses like wake up command generator for other onboard devices/microcontrollers, trigger for sensors like DHT22, etc.

Hardware Connection


Code Example

#include "STM8S.h"

void clock_setup(void);
void GPIO_setup(void);
void TIM1_setup(void);

void main(void)


void clock_setup(void)

       while(CLK_GetFlagStatus(CLK_FLAG_HSERDY) == FALSE);


       while(CLK_GetFlagStatus(CLK_FLAG_HSIRDY) == FALSE);



       CLK_PeripheralClockConfig(CLK_PERIPHERAL_TIMER1, 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_UART2, DISABLE);
       CLK_PeripheralClockConfig(CLK_PERIPHERAL_TIMER2, DISABLE);
       CLK_PeripheralClockConfig(CLK_PERIPHERAL_TIMER3, DISABLE);
       CLK_PeripheralClockConfig(CLK_PERIPHERAL_TIMER4, DISABLE);

void GPIO_setup(void)
       GPIO_WriteHigh(GPIOC, GPIO_PIN_4);

void TIM1_setup(void)

       TIM1_TimeBaseInit(160, TIM1_COUNTERMODE_UP, 10000, 1);





Firstly, the peripheral and CPU clocks are set at max speed:


TIM1 is setup is as simply as we would do for PWM generation. However, for one pulse mode (OPM) we must select one pulse mode.

void TIM1_setup(void)

       TIM1_TimeBaseInit(160, TIM1_COUNTERMODE_UP, 10000, 1);



At this point it is necessary to describe TIM1 PWM modes. There are two PWM mode – PWM mode 1 and PWM mode 2.

PWM Mode 1

In up-counting mode, the channel is active if the counter is less than CCR1 or else it is inactive.
The opposite is true in down-counting mode.

PWM Mode 2

The channel is inactive as long as the counter is less than CCR1 in up- counting mode.

For OPM example here, we need PWM mode 2.

In this example the pulse width time of the one pulse is about 0.25ms and has a delay of 0.375ms. The calculation is very simple. Since 16MHz clock is used, one cycle takes 62.5ns and so 10000 counts equal 0.625ms. Because we are using PWM mode 2, it will take more than 6000 counts or 0.375ms before the one pulse start. The pulse has a width of (10000 – 6000) = 4000 counts or 0.25ms and will end after this time.




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  • hi
    i copied all the above (UART interrupt) code as directed (without any changing). only i added stm8s_delay.h.
    but this error occurs

    #error clnk Debug\mgstm_1007.lkf:86 Debug\stm8_interrupt_vector.o: symbol f_NonHandledInterrupt multiply defined (Debug\stm8s_it.o)

    please guide

  • Example with an encoder. The counter only counts up, regardless of the direction of rotation of the encoder. Where could be the problem?

  • How to fight trash data on ADC inputs? Even when I don’t connect any voltage source it shows some data.

  • Hello, the interrupt handling is different from what the datasheet says. To clear the flag just read the SR and DR registers. In addition, if the 4 LSB of SR reports an error, there may not be an interruption, it is necessary to monitor these errors as well, and clean the register, as the datasheet says, I noticed this using an STM8S003F3, I don’t know if this happens with other models.

  • why are the lines


    written inside the while loop? Shouldn’t we set them once?

  • I’m programming in IAR and just have noticed that the file stm8_interrupt_vector.c is missing. I found it under …\STM8S_StdPeriph_Lib\Project\STM8S_StdPeriph_Template\STVD\Cosmic and included it into my workspace. But during the making it gives out a bunch of errors. I could I solve this?

  • I enjoyed the tutorial. Thank you. Just one question: is it fine that my counter is incrementing in 2 instead of 1 while I turn the encoder?

  • Sir can i use this code for ILI9488 SPI TFT display of 320(RGB) x 480 Resolution?

  • Hello sir i am Chavda hiren

    this timer is STVD is ok
    But i Need This Timer a IAR IDE
    Can you Plz Sir

    void TIM2_setup(void)
    TIM2_TimeBaseInit(TIM2_PRESCALER_32, 1250);

    Thank you

  • Shahryiar,
    I am working with your code related to ST7735 TFT Display. When compiling COSMIC compiler is giving me an error for ST7735.c file and the error is as follows:

    st7735.c:389(11) missing prototype

    On line 389 of the ST7735.c is “swap(&y1, &y2);”
    My question is where is the function defined for “swap”?

    Thanks in advance

  • naveed ahmed siddiqui

    Dear sir i have problem to use ram size of stm8s003k3
    how can i use 1024 byte for serial received
    please replay me i am waiting

  • Hi Shawon Shahryiar,

    You mentioned this *”IAP can also be used for upgrading application firmware Over-The-Air (OTA)”* in this blog at the beginning, what does this mean?

    And I know that STM32 is also not a wireless MCU but there are some solutions to upgrade firmware using ESP8266 and Bluetooth module through UART.

    ( ) I found this above source code as example of implementation of bootloader, please help me with this.

    ( ) and also this as a customised bootloader,

    ( ). I raised a question in ST community about this and they told it is possible to use UBC(User Boot Code) area to update firmware. Please check and help me, may be it helps everyone.



  • 1. Do wfi() and halt() have the same power savings?

    2. If halt() is called, can the microcontroller still be woken up by an interrupt?

  • Hi Shawon

    Thank you for these excellent tutorials.

    I was just wondering why you use two output channels on TIM2? Do you connect them in parallel?

  • Hello all embedded people, my application is to read pwm on a pin for rise edge or fall edge (ANYEDGE) and produce a pwm signal with different duty cycle on another pin (without any button pressed).

    Can anyone explain me how to use this example for my application? please help me 🙂

  • Thanks for useful tutorials
    How can I store/initialize byte data into EEPROM at the time of programming?


  • Gostei muito bom.

  • Hello Shawon,
    Thank you for your great tutorials.

    Could you please help me with NEC IR decoding using stm8s.

  • I want to use multichannel adc interrupt for eg (channel 2 ,3,4 of ADC1 ) but when i do this i got value from a single channel in all three buffer value. what i should do for correct data?? please suggest

  • hi again
    an other problem! 🙁
    i want to use multi channel “scan mode” only for 2 channel(CH2,CH3) and i used other adc pins for gpio purposes.
    but… when adc runs and turns on, gpio pins become noisy!!!
    whats problem?

  • hi shawon
    i want to read “ADC1_GetBufferValue(0)” in timer interrupt… but it returns 0 !!!! (in the main.c it’s ok)
    how can i do it?

  • First I want to say thank you for your useful tutorial.
    then I have a question:
    I need to store one byte data either on EEPROM or FLash memory. the problem is I need to write it into the memory every 5 minutes.
    The datasheet says that the EEPROM can work for 100K cycles of erase/write, and that’s not enough for a long-time use of the device.
    I want to know how many times (cycles) we can erase/write to an address on Flash memory.
    thanks a lot

  • Hi
    This is an excellent series of tutorial. I appreciate your efforts. I’m using the similar multi-channel ADC to read data from channel 3 and 7. But the problem that I have is, the ADC value doesn’t seem to update automatically, I need to reset it in order to get the updated data. Is there anything I’m missing in the ADC1 configuration that causes it? Thanks

  • This code is very helpful, that you for showing it. There doesn’t seem to be a lot of documentation or resources for these processors, but their price makes them very attractive.

    In my application, I use AIN2 and AIN3 since the pins for the other channels are required for other functionality. I am wondering if there is a way to just read those channels individually when I need to without having to scan channels 0-3 each time and without having to call a reconfiguration routine to switch between channels 2 and 3?

  • Hi. I’m using the STVD IDE with Cosmic with an STM8TL52F4 MCU with the ‘Minimize Code Size’ compiler option selected. Under Debug instrument->ICD MCU configuration->Options, I set the DATASIZE_bit6 Value to 1 (the other DATASIZE bits are 0) and made no other changes there. As I understand it, that should reserve a 1024 byte window near the end of EEPROM for my permanent (power-up to power-up) settings info starting at address 0x0800. I’m able to UNLOCK, write and read that area and LOCK it again without problems. However, with each debug session, I find that the area is always overwritten. How do I prevent that and keep that area secure? And I’m curious what it’s being overwritten WITH? I’m doing just as this demo suggests.

  • Hi Shawon. How to take more than one measurement with interrupt. Example AIN5 and AIN6 measurement with interrupt ?

  • I use Eclipse & sdcc .
    void timer1_CAP_isr (void) __interrupt (12) {
    I have the following error.
    Unused declaration of function ‘timer1_CAP_isr’
    But the interruption doesn’t work

    • The code is written with STVD and the compiler is Cosmic C. Surely it won’t work with other compilers but the concept would work. Thanks.

      • Hi Sharon,

        Is the delay necessary for the programming action?

        I used roughly the same method(but I did not add a delay but only a EOP flag check) and did a action check after programming it works fine at start but as soon as I restart the thing and the code reads old data from the same eeprom address like the programming action never occurred.

  • Shawon,

    Your inspirational blog has gotten me started with STM32 and STM8s micros. You have done a marvelous job in explaining each aspect of the hardware in each of these micros and the example code is well written. Thank you so much for taking the time to put this together for all to use.

    Thank you,
    Adil Khan

  • Hello… Can you suggest me an evaluation kit/development kit for STM8S105S4T6C micro-controller? I need this controller for BLDC Motor control

  • Hi Shawon Shahryiar,

    I am using stm8s003f3 discovery board. In my project, I am using ADC1 multiple channels 0,1,2,3. In these four channels, I am using 0,1,3 as a normal ADC read and channel 2 as an interrupt based.
    I am facing a problem that if configure ADC channel 0,1,3 and read value then ADC interrupts not occurred.
    But if I comment multiple channels read then interrupt occurred.

    Can you tell me why it is like that and can I read adc1 multi-channel with interrupt-based?

    Channel0,1,3 read normal ADC from 3 potentiometers and only channel 2 as an interrupt based.

    • In my write up I stated “In scan mode, the ADC automatically scans a sequence of channels from channel 0 to channel n, keeping the results of AD conversion in data buffer registers. At the end of conversion, the results are ready to be read.” and so in your case it is not like 0 > 1 > 2 > 3…. 2 is missing in the scan sequence and so it will probably not work….

      • Hi Hi, Shawon Shahryiar,

        Might be this is possible but my question is different.
        My question is:- Can I use multichannel ADC with scan mode and ADC interrupt based at the same time with the diffrent channels?
        Example:- Channel 0,1 as a scan mode and channel 2 as an ADC interrupt based simultaneously?

    • Hey i am also using same controller and using single ADC pin but adc value is fluctuating continuously without any input.can u please tell me why this is happening and what is the solution.

  • Normally I don’t learn article on blogs, however
    I wish to say that this write-up very pressured me to check out and do it!
    Your writing taste has been surprised me. Thank you, very nice article.

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  • Dear Shawon,
    Thank you for your useful website and articles.
    I have taken a look at ADC1_Init definition and I found it uses ADC1_ConversionConfig to set channels and conversion mode. So it seems using ADC1_Init once with all needed channels is enough. Am I right?
    Thank you very much.

  • Hello,
    I am learning stm8s, but i have a project in my mind, i am making Pong game with two encoders and PCD8544 LCD. Your tutorials are great and it’s very big source of knowledge for me, and i have a question about this article:
    Is it possible to use two encoder this way? Or can it be done in the other way? I have stm8s103f3p6, and i know it has 4 interrupt pins, so I thought about using these for two encoders, but then i saw your article about QEI

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    Would you have an example 433 mhz rf signal capture with flash code writing?

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  • Hi,
    Thats great work
    Do you have steps for to work ST7735 TFT IN 8 BIT 8080 mode

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    Thanks Shawon, your blogs are indeed very helpful. Keep Growing.

  • why are you sending the received data back through TX pin?


    I am wondering how to get a Max31855 to talk to a STM8s via SPI.


    • What’s to wonder about it? It is a simple SPI communication and SPI for STM8 is no different from the SPI of other MCUs…. The following lines are taken from the device’s datasheet and the write up there states how to communicate with it:

      “Drive CS low to output the first bit on the SO pin. A complete serial-interface read of the cold-junction compensated thermocouple temperature requires 14 clock cycles. Thirty-two clock cycles are required to read both the thermocouple and reference junction temperatures (Table 2 and Table 3.) The first bit, D31, is the thermocouple temperature sign bit, and is presented to the SO pin within tDV of the falling edge of CS. Bits D[30:18] contain the converted temperature in the order of MSB to LSB, and are presented to the SO pin within tD0 of the falling edge of SCK. Bit D16 is normally low and goes high when the thermocouple input is open or shorted to GND or VCC. The reference junction temperature data begins with D15. CS can be taken high at any point while clocking out con-version data. If T+ and T- are unconnected, the thermocouple temperature sign bit (D31) is 0, and the remainder of the thermocouple temperature value (D[30:18]) is 1.”

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