Continuing the STM8 Expedition

This post is the continuation of the first post on STM8 microcontrollers here.

STM8S105 Discovery

ADC Interrupt

Instead of polling for ADC’s end of conversion (EOC) state, it is wise to use ADC interrupt. Just as with any hardware peripheral, interrupt methods make a system highly responsive. Interrupts like these free up the CPU for other tasks. However, it is up to the coder to determine interrupt priorities and look out for situation that may cause too many interrupts to be processed in a short while.

Hardware Connection


Code Example


stm8s_it.h (top part only)

#ifndef __STM8S_IT_H
#define __STM8S_IT_H

@far @interrupt void ADC_IRQHandler(void);

/* Includes ------------------------------------------------------------------*/
#include "stm8s.h"


stm8s_it.c (top part only)

#include "stm8s.h"
#include "stm8s_it.h"

extern unsigned int adc_value;

void ADC_IRQHandler(void)
       adc_value = ADC1_GetConversionValue();


stm8_interrupt_vector.c (shortened)

#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, (interrupt_handler_t)ADC_IRQHandler}, /* irq22 */
       {0x82, NonHandledInterrupt}, /* irq29 */



#include "STM8S.h"
#include "lcd.h"

unsigned int adc_value;

unsigned char bl_state;
unsigned char data_value;

void clock_setup(void);
void GPIO_setup(void);
void ADC1_setup(void);
void lcd_print(unsigned char x_pos, unsigned char y_pos, unsigned int value);

void main(void)
       float mv = 0x00000000;



       LCD_goto(2, 0);
       LCD_putstr("STM8 ADC ISR");
       LCD_goto(0, 1);


              mv = (adc_value * 5000.0);
              mv /= 1023.0;

              lcd_print(7, 1, mv);            
              lcd_print(12, 1, adc_value);
              GPIO_WriteReverse(GPIOD, GPIO_PIN_0);

void clock_setup(void)

       while(CLK_GetFlagStatus(CLK_FLAG_HSIRDY) == FALSE);



       CLK_PeripheralClockConfig(CLK_PERIPHERAL_I2C, ENABLE);
       CLK_PeripheralClockConfig(CLK_PERIPHERAL_ADC, ENABLE);
       CLK_PeripheralClockConfig(CLK_PERIPHERAL_SPI, 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_Init(GPIOB, ((GPIO_Pin_TypeDef)(GPIO_PIN_0 | GPIO_PIN_1)),      GPIO_MODE_IN_FL_NO_IT);


void ADC1_setup(void)


       ADC1_ITConfig(ADC1_IT_EOCIE, ENABLE);

void lcd_print(unsigned char x_pos, unsigned char y_pos, unsigned int value)
       char chr = 0x00;

       chr = ((value / 1000) + 0x30);  
       LCD_goto(x_pos, y_pos);

       chr = (((value / 100) % 10) + 0x30);
       LCD_goto((x_pos + 1), y_pos);

       chr = (((value / 10) % 10) + 0x30);
       LCD_goto((x_pos + 2), y_pos);

       chr = ((value % 10) + 0x30);
       LCD_goto((x_pos + 3), y_pos);



This example and the first ADC example is all same except for the interrupt part. Note the last three lines below.

void ADC1_setup(void)


       ADC1_ITConfig(ADC1_IT_EOCIE, ENABLE);

As can be seen, End-of-Conversion (EOC) interrupt has been enabled along with global interrupt and the ADC itself.

In the vector mapping file, ADC interrupt is set.

{0x82, (interrupt_handler_t)ADC_IRQHandler}, /* irq22 */

When ADC EOC interrupt triggers, the ADC data buffer is read and the EOC flag is cleared.

void ADC_IRQHandler(void)
       adc_value = ADC1_GetConversionValue();




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  • 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

    • 100k Cycles @ 5 min = 300 hours approximately. The device won’t last even a year. Better use battery-backed RAM or store your data in MCU’s SRAM and have it written to EEPROM/flash only at the event of a power failure.

  • 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

  • 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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    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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