Continuing the STM8 Expedition

STM8S105 Discovery

Multi-Channel ADC with Scan Mode

When it is required to sense and measure multiple analog voltages, we need to use multiple ADC channels. For example, when we need to build, an electrical energy meter, we need to measure both voltage and current. However, STM8S003K3 has one ADC which is multiplexed over four channels. This does not limit it from acquiring multiple analog signals and the job is easily achieved using ADC scan mode conversion.

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.

Hardware Connection

adc_scan

Code Example

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


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()
{
       unsigned int A0 = 0x0000;
       unsigned int A1 = 0x0000;

       clock_setup();
       GPIO_setup();
       ADC1_setup();

       LCD_init(); 
       LCD_clear_home();

       LCD_goto(1, 0);
       LCD_putstr("STM8 Multi-ADC");
       LCD_goto(0, 1);
       LCD_putstr("A0");
       LCD_goto(9, 1);
       LCD_putstr("A1");

       while(TRUE)
       {
              ADC1_ScanModeCmd(ENABLE);
              ADC1_StartConversion();
              while(ADC1_GetFlagStatus(ADC1_FLAG_EOC) == FALSE);

              ADC1_ClearFlag(ADC1_FLAG_EOC);

              A0 = ADC1_GetBufferValue(0);
              A1 = ADC1_GetBufferValue(1);

              lcd_print(3, 1, A0);
              lcd_print(12, 1, A1);
              delay_ms(90);
       };
}


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_HSIDIV4);
       CLK_SYSCLKConfig(CLK_PRESCALER_CPUDIV1);

       CLK_ClockSwitchConfig(CLK_SWITCHMODE_AUTO, CLK_SOURCE_HSI,
       DISABLE, CLK_CURRENTCLOCKSTATE_ENABLE);

       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_DeInit(GPIOB);
       GPIO_Init(GPIOB, ((GPIO_Pin_TypeDef)(GPIO_PIN_0 | GPIO_PIN_1)), GPIO_MODE_IN_FL_NO_IT);

       GPIO_DeInit(GPIOD);
       GPIO_Init(GPIOD, GPIO_PIN_0, GPIO_MODE_OUT_OD_HIZ_FAST);
}


void ADC1_setup(void)
{
       ADC1_DeInit();     

       ADC1_Init(ADC1_CONVERSIONMODE_CONTINUOUS,
                 ADC1_CHANNEL_0,
                 ADC1_PRESSEL_FCPU_D18,
                 ADC1_EXTTRIG_GPIO,
                 DISABLE,
                 ADC1_ALIGN_RIGHT,
                 ADC1_SCHMITTTRIG_CHANNEL0,
                 DISABLE);

       ADC1_Init(ADC1_CONVERSIONMODE_CONTINUOUS,
                 ADC1_CHANNEL_1,
                 ADC1_PRESSEL_FCPU_D18,
                 ADC1_EXTTRIG_GPIO,
                 DISABLE,
                  ADC1_ALIGN_RIGHT,
                  ADC1_SCHMITTTRIG_CHANNEL1,
                  DISABLE);

       ADC1_ConversionConfig(ADC1_CONVERSIONMODE_CONTINUOUS,
                                                                                  ((ADC1_Channel_TypeDef)(ADC1_CHANNEL_0 | ADC1_CHANNEL_1)),
                                                                                  ADC1_ALIGN_RIGHT);

       ADC1_DataBufferCmd(ENABLE);
       ADC1_Cmd(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);
       LCD_putchar(chr);

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

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

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

 

Explanation

The setup here is same as the setup for the other ADC examples. There are a few difference though. Firstly, the channel configuration. Note that here two channels are used and are independently configured. This is so because each channel may have different properties. Secondly, conversion mode and data alignments are set. Thirdly, data buffers are enabled to capture ADC data on different channels.

void ADC1_setup(void)
{
       ADC1_DeInit();     

       ADC1_Init(ADC1_CONVERSIONMODE_CONTINUOUS,
                 ADC1_CHANNEL_0,
                 ADC1_PRESSEL_FCPU_D18,
                 ADC1_EXTTRIG_GPIO,
                 DISABLE,
                 ADC1_ALIGN_RIGHT,
                 ADC1_SCHMITTTRIG_CHANNEL0,
                 DISABLE);

       ADC1_Init(ADC1_CONVERSIONMODE_CONTINUOUS,
                 ADC1_CHANNEL_1,
                 ADC1_PRESSEL_FCPU_D18,
                 ADC1_EXTTRIG_GPIO,
                 DISABLE,
                 ADC1_ALIGN_RIGHT,
                 ADC1_SCHMITTTRIG_CHANNEL1,
                 DISABLE);

       ADC1_ConversionConfig(ADC1_CONVERSIONMODE_CONTINUOUS,
                                                                                  ((ADC1_Channel_TypeDef)(ADC1_CHANNEL_0 | ADC1_CHANNEL_1)),
                                                                                  ADC1_ALIGN_RIGHT);

       ADC1_DataBufferCmd(ENABLE);
       ADC1_Cmd(ENABLE);
}

Polling method is used to start and extract ADC data. Firstly, the ADC is told to do scan conversion. The conversion is then started. We, then, poll the end-of-conversion condition (EOC) status. EOC notifies that all ADC data have been captured and a scan has successfully completed. Finally, the EOC flag is cleared and the data are read from separate data buffers. Everytime a new scan is started the previous buffer data are cleared and are updated with new ones.

ADC1_ScanModeCmd(ENABLE);
ADC1_StartConversion();
while(ADC1_GetFlagStatus(ADC1_FLAG_EOC) == FALSE);

ADC1_ClearFlag(ADC1_FLAG_EOC);

A0 = ADC1_GetBufferValue(0);
A1 = ADC1_GetBufferValue(1);

 

Demo

Scan Mode ADC (1) Scan Mode ADC (2)

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