Successive Comparative ADC

This post describes successive comparison type ADCs.

The ADC in most MCUs is a successive comparison type ADC as shown in the figure below. Since the successive comparison type ADC compares V_IN with V_REF/2^m, the value of V_IN is obtained by the following equation.

V_IN = ( ADC data register value × V_REF ) / 2ⁿ

Examples of ADC programs that take into account various issues

1. Check if ADC is running
2. ADC Start & Check
3. Timeout when ADC is not completed within a predetermined time
   ADC conversion time varies with ADC 2ⁿ bits, so timeout TIME_OUT_ADC is also adjusted.
4. ADC read

#define TIME_OUT_ADC 10      // 10[us]

// Sample HAL function
int hal_adc_status( int );   // ADC status read function
int hal_adc_start( int );    // ADC start function
int hal_adc_read( int );     // ADC read function
bool time_out( int );        // Time out function [us]

int ADC_Read( int ch)
{
    bool flag = FALSE;
    int  val  = 0;
    // Check if ADC is running
    if( hal_adc_status( ch ) == ADC_FIN )
    {
        // ADC start
        if( hal_adc_start( ch ) == ADC_EXE )
        {
            flag = TRUE;
            do{
　　　　　　    // Check Time out
                if( time_out( TIME_OUT_ADC ) == TRUE )
                {
                    flag = FALSE;
                    break;
                }
            // Check ADC fin
            }while( hal_adc_status( ch ) == ADC_FIN )
        }
    }
    if( flag == TRUE )
    {
        // ADC read
        val = hal_adc_read( ch );
    }
    return( val );
}

Simple ADC program example

1. ADC start and ADC conversion wait, ADC read

// Sample HAL function
int hal_adc_start_read( int );     // ADC start & read function

int ADC_Read( int ch)
{
    // ADC start & read
    return( hal_adc_start_read( ch ) );
}