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Multiple ADC channels with some incorrect value

Copper

Hi,

I'm using S7A3 MCU, SSP 2.4.0

Trying to measure 16 analog input using ADC14. The ADC read that return few channel is lower than other. I measure the voltage at the ADC input pins and it has the same voltage as other input. my code is below

    volatile bool               adc_convert_complete = false;
    uint16_t                    adcBuffer[16];
    adc_register_t              adcChannel[] = {ADC_REG_CHANNEL_0, ADC_REG_CHANNEL_1, ADC_REG_CHANNEL_2,
                                            ADC_REG_CHANNEL_3, ADC_REG_CHANNEL_4, ADC_REG_CHANNEL_5,
                                            ADC_REG_CHANNEL_6, ADC_REG_CHANNEL_7, ADC_REG_CHANNEL_8,
                                            ADC_REG_CHANNEL_16, ADC_REG_CHANNEL_17, ADC_REG_CHANNEL_18,
                                            ADC_REG_CHANNEL_19, ADC_REG_CHANNEL_20, ADC_REG_CHANNEL_21,
                                            ADC_REG_CHANNEL_22};
    
    g_adc0.p_api->open(g_adc0.p_ctrl, g_adc0.p_cfg);
    
    R_S14ADC->ADHVREFCNT_b.HVSEL = 1;
    R_S14ADC->ADHVREFCNT_b.LVSEL = 1;
    R_S14ADC->ADCSR_b.ADHSC = 0;            // High speed A/D conversion
    R_S14ADC->ADSSTR0n_b[0].SST = 38;
    R_S14ADC->ADSSTRO_b.SST = 38;
    
    status =  g_adc0.p_api->scanCfg(g_adc0.p_ctrl, g_adc0.p_channel_cfg);
    
    while(1)
    {
        g_adc0.p_api->scanStart(g_adc0.p_ctrl);

        while (adc_convert_complete == false);           
        adc_convert_complete = false;                    

    
        for (int i = 0; i < 16; i++)
        {
            g_adc0.p_api->read(g_adc0.p_ctrl,  adcChannel[i], &adcBuffer[i]);
        }
        g_adc0.p_api->scanStop(g_adc0.p_ctrl);
    
        tx_thread_sleep (100);
    }

void mcu_adc_callback (adc_callback_args_t *p_args)
{
    SSP_PARAMETER_NOT_USED(p_args);
    adc_convert_complete = true;
}

The conversion is show below: Channels in green boxes are measured that all having the same voltage input. However, couple channels with red arrows are reading lower than others. The channels with read arrows read correctly when I significantly lower  the input voltage level.

Is there anything I did wrong? Does it require to be calibrated (how)

Thanks,

Parents Reply
  • 0 in reply to Jayesh (SWF)

    Hi Jayesh,

    It is a complex circuit with many multiplexer switches. However, in this case, I measure the voltage at the MCU analog input pin to verify that the tolerance of the MUX would not be the cause. and yes, the voltage input is correct, but the conversion is not.

    The board is completed PCBA, I can't swap the channel but will try with different board to see if it behaves the same.

    Regards,  

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