Starting STM8 Microcontrollers

STM8S003K3 Discovery

Serial Communication (UART)

Serial communication is perhaps the mostly-used classic communication method for interfacing a PC or other machines with a micro. With just two wire, we can achieve a full-duplex point-to-point communication. Owing to its simplicity and wide usage, it is the communication interface backbone that is used with GSM modems, RF modules, Bluetooth devices like RN-52, Wi-Fi devices like the popular ESP8266, etc. It is also widely used in industries. Other communications rely on it, for example, RS-485, LIN, etc.

 PPT

Most STM8s have at least one UART module. Some have more than one. Different UARTs have different features as shown:

UARTs

To learn more about UART visit the following link:

https://learn.mikroe.com/uart-serial-communication/

The UARTs of STM8 micros are so robust and packed with so many features that it is quite impossible to explain them all in this one article. Here we will explore the basic serial communication only.  LIN and IRDA will hopefully be covered in future articles.

Hardware Connection

Cubemx

 

Code Example

#include "STM8S.h"
 
 
void clock_setup(void);
void GPIO_setup(void);
void UART1_setup(void);
 
 
void main(void)
{
     unsigned char i = 0;   
     char ch = 0;
                
     clock_setup();
     GPIO_setup();
     UART1_setup();
     LCD_init();
     LCD_clear_home();
                
     LCD_goto(0, 0);
     LCD_putstr("TX:");
     LCD_goto(0, 1);
     LCD_putstr("RX:");
                
     while(TRUE)
     {
          if(UART1_GetFlagStatus(UART1_FLAG_RXNE) == TRUE)
          {
             ch = UART1_ReceiveData8();
             LCD_goto(7, 1);
             LCD_putchar(ch);
             UART1_ClearFlag(UART1_FLAG_RXNE);
             UART1_SendData8(i + 0x30);
          }
          
          if(UART1_GetFlagStatus(UART1_FLAG_TXE) == FALSE)
          {
             LCD_goto(7, 0);
             LCD_putchar(i + 0x30);
             i++;
          }
      };
}
 
 
void clock_setup(void)
{
      CLK_DeInit();
                
      CLK_HSECmd(DISABLE);
      CLK_LSICmd(DISABLE);
      CLK_HSICmd(ENABLE);
      while(CLK_GetFlagStatus(CLK_FLAG_HSIRDY) == FALSE);
                
      CLK_ClockSwitchCmd(ENABLE);
      CLK_HSIPrescalerConfig(CLK_PRESCALER_HSIDIV8);
      CLK_SYSCLKConfig(CLK_PRESCALER_CPUDIV1);
                
      CLK_ClockSwitchConfig(CLK_SWITCHMODE_AUTO, CLK_SOURCE_HSI, 
      DISABLE, CLK_CURRENTCLOCKSTATE_ENABLE);
                
      CLK_PeripheralClockConfig(CLK_PERIPHERAL_I2C, DISABLE);
      CLK_PeripheralClockConfig(CLK_PERIPHERAL_SPI, DISABLE);
      CLK_PeripheralClockConfig(CLK_PERIPHERAL_ADC, DISABLE);
      CLK_PeripheralClockConfig(CLK_PERIPHERAL_AWU, DISABLE);
      CLK_PeripheralClockConfig(CLK_PERIPHERAL_UART1, ENABLE);           
      CLK_PeripheralClockConfig(CLK_PERIPHERAL_TIMER1, DISABLE);
      CLK_PeripheralClockConfig(CLK_PERIPHERAL_TIMER2, DISABLE);
      CLK_PeripheralClockConfig(CLK_PERIPHERAL_TIMER4, DISABLE);
}
 
 
void GPIO_setup(void)
{                               
     GPIO_DeInit(GPIOD);
                
     GPIO_Init(GPIOD, GPIO_PIN_5, GPIO_MODE_OUT_PP_HIGH_FAST);
     GPIO_Init(GPIOD, GPIO_PIN_6, GPIO_MODE_IN_PU_NO_IT);
}
 
 
void UART1_setup(void)
{
     UART1_DeInit();
                
     UART1_Init(9600, 
                UART1_WORDLENGTH_8D, 
                UART1_STOPBITS_1, 
                UART1_PARITY_NO, 
                UART1_SYNCMODE_CLOCK_DISABLE, 
                UART1_MODE_TXRX_ENABLE);
                
     UART1_Cmd(ENABLE);
}

 

Explanation

The peripheral and CPU clocks are set at 2MHz:

CLK_HSIPrescalerConfig(CLK_PRESCALER_HSIDIV8);
CLK_SYSCLKConfig(CLK_PRESCALER_CPUDIV1);
….
….
CLK_PeripheralClockConfig(CLK_PERIPHERAL_UART1, ENABLE);

The TX-RX GPIO pins are set as output and input respectively:

GPIO_DeInit(GPIOD);
                
GPIO_Init(GPIOD, GPIO_PIN_5, GPIO_MODE_OUT_PP_HIGH_FAST);
GPIO_Init(GPIOD, GPIO_PIN_6, GPIO_MODE_IN_PU_NO_IT);

UART setup is straightforward. We just need to set baud rate, no. of data bits, no. of stop bit, parity and type of communication (synchronous or asynchronous).

void UART1_setup(void)
{
     UART1_DeInit();
                
     UART1_Init(9600, 
                UART1_WORDLENGTH_8D, 
                UART1_STOPBITS_1, 
                UART1_PARITY_NO, 
                UART1_SYNCMODE_CLOCK_DISABLE, 
                UART1_MODE_TXRX_ENABLE);
                
     UART1_Cmd(ENABLE);
}

In the main code, we are checking both transmission complete and reception complete flags. With these flags, we will know if new data arrived and if it is possible to send a new data.

The first part checks if any new data received. That’s why the IF condition is checking if the RX buffer is empty or not. If it is not empty then new data must have arrived. The new data (a character here) is fetched and displayed on a LCD. Then we clear the RX buffer not empty flag to enable reception of new data. After that we are sending some data to the host PC over the UART.

if(UART1_GetFlagStatus(UART1_FLAG_RXNE) == TRUE)
{
   ch = UART1_ReceiveData8();
   LCD_goto(7, 1);
   LCD_putchar(ch);
   UART1_ClearFlag(UART1_FLAG_RXNE);
   UART1_SendData8(i + 0x30);
}

In the second part, we are checking if the last data was sent from our STM8 micro. The data sent is then displayed on LCD. 

if(UART1_GetFlagStatus(UART1_FLAG_TXE) == FALSE)
{
   LCD_goto(7, 0);
   LCD_putchar(i + 0x30);
   i++;
}

Please note that both of these flags are very important.

 

Demo

UART

Untitled

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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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