CCS/TMS320F28335: How to read ADC mirror correctly?

Ata Khiabani

Tool/software: Code Composer Studio

Hello

I want to read three voltage values with ADC, these values are not in the range of 0-3V so using op-amp, I attenuate them (with factor q) and then add them with a constant voltage (p) to get a voltage in 0-3V and then read this with ADC.

My questions:

1. After reading this value, I subtract the added voltage from the result and then multiply it with q to get my actual voltage. Should I use ADC mirror registers or ADC result registers? So far I have been doing the following code with no result:

AdcRegs.ADCMAXCONV.all = 0x0003;       // Setup 2 conv's on SEQ1
    AdcRegs.ADCCHSELSEQ1.bit.CONV00 = 0x2; // Setup ADCINA2 as 1st SEQ1 conv.
    AdcRegs.ADCCHSELSEQ1.bit.CONV01 = 0x3; // Setup ADCINA3 as 2nd SEQ1 conv.
    AdcRegs.ADCCHSELSEQ1.bit.CONV02 = 0x4;

AdcRegs.ADCTRL1.bit.ACQ_PS=0x3;
    AdcRegs.ADCTRL2.bit.EPWM_SOCA_SEQ1 = 1;

    AdcRegs.ADCTRL2.bit.INT_ENA_SEQ1 = 1;  // Enable SEQ1 interrupt (every EOS)

EPwm1Regs.ETSEL.bit.SOCAEN = 1;     // Enable SOC on A group
    EPwm1Regs.ETSEL.bit.SOCASEL = 4;    // Select SOC from from CPMA on upcount
    EPwm1Regs.ETPS.bit.SOCAPRD = 1;     // Generate pulse on 1st event
    EPwm1Regs.CMPA.half.CMPA = 0x0080;  // Set compare A value
    EPwm1Regs.TBPRD = 0xC8;           // Set period for ePWM1
    EPwm1Regs.TBCTL.bit.CTRMODE = 0;    // count up and start

__interrupt void
adc_isr(void)
{


#define offset2 0x7BB;




    Voltage1 = AdcMirror.ADCRESULT0-offset1;
    Voltage2 = AdcMirror.ADCRESULT1-offset1;
    Voltage3 = AdcMirror.ADCRESULT2-offset1;

    current = (Voltage1-Voltage2);
    voltage = (Voltage2-Voltage3);


    AdcRegs.ADCTRL2.bit.RST_SEQ1 = 1;         // Reset SEQ1
    AdcRegs.ADCST.bit.INT_SEQ1_CLR = 1;       // Clear INT SEQ1 bit
    PieCtrlRegs.PIEACK.all = PIEACK_GROUP1;   // Acknowledge interrupt to PIE

    return;
}

2. I have defined A2,A3,A4 as my channels and I use them. however when I check the ADC registers, 4 of them has values (ADCRESULT0, ADCRESULT1, ADCRESULT2, ADCRESULT3). Shouldn't it be three registers? I mean how should I read these four registers if I only have 3 channels?

Regards,

Ata

over 9 years ago

0 tlee over 9 years ago

TI__Guru 62975 points

Ata Khiabani said:
After reading this value, I subtract the added voltage from the result and then multiply it with q to get my actual voltage. Should I use ADC mirror registers or ADC result registers? So far I have been doing the following code with no result:

This sounds like an acceptable approach assuming that your offset is normalized to a 12-bit conversion value. Beware that most variables are declared as unsigned integers, which would be problematic if your offset has a larger magnitude than the ADC result.

Ata Khiabani said:
I have defined A2,A3,A4 as my channels and I use them. however when I check the ADC registers, 4 of them has values (ADCRESULT0, ADCRESULT1, ADCRESULT2, ADCRESULT3). Shouldn't it be three registers? I mean how should I read these four registers if I only have 3 channels?

You initialized four conversions when you executed this statement:

AdcRegs.ADCMAXCONV.all = 0x0003;

As shown in the ADC Reference Guide:

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CCS/TMS320F28335: How to read ADC mirror correctly?