CCS/MSP430FR5969: Using 12b ADC Pro to get correct FFT on ADC Pro

Connor Connaughton

Part Number: MSP430FR5969
Other Parts Discussed in Thread: ADS8881,

Tool/software: Code Composer Studio

Hi,

I am currently working on a project that is comparing the ADC performance of the external ADC (ADS8881) and the internal 12b ADC of the MSP430FR5969. I am able to replicate the signal on the ADS8881EVM GUI.

As for the MSP430 12b ADC data, I upload it with the correct formatting into ADC Pro, where I do get a correct signal in the Multi Scope function (see attached)

But the problem that I am running into is running the FFT. My SNR performance is -1.76dB. Which I believe to be very low. (attached).

My input frequency is 6 Hz into the 12b internal ADC. Is there a reason for this poor performance? Is it related to my input signal or the data I have been receiving from the 12b ADC.

As for my ADC configuration settings, attached is my code as well.

Fullscreen MSP430 ADC Code.txt Download

#include <msp430.h>
int temp;
unsigned int ADC_val[512];
unsigned int counter = 0;
int main(void)
{
  WDTCTL = WDTPW | WDTHOLD;                 // Stop WDT

  // GPIO Setup
  P1OUT &= ~BIT0;                           // Clear LED to start
  P1DIR |= BIT0;                            // Set P1.0/LED to output
  P1SEL1 |= BIT5;                           // Configure P1.1 for ADC
  P1SEL0 |= BIT5;

  // Disable the GPIO power-on default high-impedance mode to activate
  // previously configured port settings
  PM5CTL0 &= ~LOCKLPM5;

  // Configure ADC12
  ADC12CTL0 = ADC12SHT0_2 | ADC12ON;        // Sampling time, S&H=16, ADC12 on
  ADC12CTL1 = ADC12SHP;                     // Use sampling timer
  ADC12CTL2 |= ADC12RES_2;                  // 12-bit conversion results
  ADC12MCTL0 |= ADC12INCH_5;                // A1 ADC input select; Vref=AVCC
  ADC12IER0 |= ADC12IE0;                    // Enable ADC conv complete interrupt

  while (1)
  {

      __delay_cycles(5000);
    ADC12CTL0 |= ADC12ENC | ADC12SC;        // Start sampling/conversion

    __bis_SR_register(LPM0_bits | GIE);     // LPM0, ADC12_ISR will force exit
    __no_operation();                       // For debugger
  }
}

#if defined(__TI_COMPILER_VERSION__) || defined(__IAR_SYSTEMS_ICC__)
#pragma vector = ADC12_VECTOR
__interrupt void ADC12_ISR(void)
#elif defined(__GNUC__)
void __attribute__ ((interrupt(ADC12_VECTOR))) ADC12_ISR (void)
#else
#error Compiler not supported!
#endif
{
  switch(__even_in_range(ADC12IV, ADC12IV_ADC12RDYIFG))
  {
    case ADC12IV_NONE:        break;        // Vector  0:  No interrupt
    case ADC12IV_ADC12OVIFG:  break;        // Vector  2:  ADC12MEMx Overflow
    case ADC12IV_ADC12TOVIFG: break;        // Vector  4:  Conversion time overflow
    case ADC12IV_ADC12HIIFG:  break;        // Vector  6:  ADC12BHI
    case ADC12IV_ADC12LOIFG:  break;        // Vector  8:  ADC12BLO
    case ADC12IV_ADC12INIFG:  break;        // Vector 10:  ADC12BIN
    case ADC12IV_ADC12IFG0:                 // Vector 12:  ADC12MEM0 Interrupt

      if(counter == 512)
          counter = 0;

     ADC_val[counter++] = ADC12MEM0;
     case ADC12IV_ADC12IFG1:   break;        // Vector 14:  ADC12MEM1
    case ADC12IV_ADC12IFG2:   break;        // Vector 16:  ADC12MEM2
    case ADC12IV_ADC12IFG3:   break;        // Vector 18:  ADC12MEM3
    case ADC12IV_ADC12IFG4:   break;        // Vector 20:  ADC12MEM4
    case ADC12IV_ADC12IFG5:   break;        // Vector 22:  ADC12MEM5
    case ADC12IV_ADC12IFG6:   break;        // Vector 24:  ADC12MEM6
    case ADC12IV_ADC12IFG7:   break;        // Vector 26:  ADC12MEM7
    case ADC12IV_ADC12IFG8:   break;        // Vector 28:  ADC12MEM8
    case ADC12IV_ADC12IFG9:   break;        // Vector 30:  ADC12MEM9
    case ADC12IV_ADC12IFG10:  break;        // Vector 32:  ADC12MEM10
    case ADC12IV_ADC12IFG11:  break;        // Vector 34:  ADC12MEM11
    case ADC12IV_ADC12IFG12:  break;        // Vector 36:  ADC12MEM12
    case ADC12IV_ADC12IFG13:  break;        // Vector 38:  ADC12MEM13
    case ADC12IV_ADC12IFG14:  break;        // Vector 40:  ADC12MEM14
    case ADC12IV_ADC12IFG15:  break;        // Vector 42:  ADC12MEM15
    case ADC12IV_ADC12IFG16:  break;        // Vector 44:  ADC12MEM16
    case ADC12IV_ADC12IFG17:  break;        // Vector 46:  ADC12MEM17
    case ADC12IV_ADC12IFG18:  break;        // Vector 48:  ADC12MEM18
    case ADC12IV_ADC12IFG19:  break;        // Vector 50:  ADC12MEM19
    case ADC12IV_ADC12IFG20:  break;        // Vector 52:  ADC12MEM20
    case ADC12IV_ADC12IFG21:  break;        // Vector 54:  ADC12MEM21
    case ADC12IV_ADC12IFG22:  break;        // Vector 56:  ADC12MEM22
    case ADC12IV_ADC12IFG23:  break;        // Vector 58:  ADC12MEM23
    case ADC12IV_ADC12IFG24:  break;        // Vector 60:  ADC12MEM24
    case ADC12IV_ADC12IFG25:  break;        // Vector 62:  ADC12MEM25
    case ADC12IV_ADC12IFG26:  break;        // Vector 64:  ADC12MEM26
    case ADC12IV_ADC12IFG27:  break;        // Vector 66:  ADC12MEM27
    case ADC12IV_ADC12IFG28:  break;        // Vector 68:  ADC12MEM28
    case ADC12IV_ADC12IFG29:  break;        // Vector 70:  ADC12MEM29
    case ADC12IV_ADC12IFG30:  break;        // Vector 72:  ADC12MEM30
    case ADC12IV_ADC12IFG31:  break;        // Vector 74:  ADC12MEM31
    case ADC12IV_ADC12RDYIFG: break;        // Vector 76:  ADC12RDY
    default: break;
  }
  __bic_SR_register_on_exit(LPM0_bits); // Exit active CPU
}

Thank you for the support!

Connor Connaughton

over 5 years ago

0 Bruce McKenney over 5 years ago

Guru 99545 points

1) You may want to try increasing the S/H time (SHT0). There's a formula in User Guide (SLAU367O) Sec 34.2.6.3, but a quick experiment would be to just, say, double it to see if it makes a difference. The ADS8881 data sheet talks about 1 Ohm input impedance (remarkable -- maybe I'm reading it wrong), while the FR5969 Ri is about 500 Ohm.

2) Are you fairly certain what your (actual) sample rate is? I'm not sure I could figure it out from just looking at the code, at least not with any precision. When I really care about this sort of thing (which is almost always) I use a timer trigger so I can publish what the rate is. Here's an Example from the suite -- focus on SHS_1 and the TA0 setup.

http://dev.ti.com/tirex/explore/node?node=AK6N6pJ.UmnfZHUCQ8HBuQ__IOGqZri__LATEST

[Edit: In that example, also note the use of CONSEQ=2 with MSC=0. This does what you want without having to toggle ENC for each sample.]

0 Connor Connaughton over 5 years ago in reply to Bruce McKenney

TI__Expert 4470 points

Hi Bruce,

Thank you. I realized that my initial problem is that I was using single conversion mode.To do this I would need to have the timer trigger the ADC to complete a conversion every 10 microseconds. Is that correct?

2) Thank you for providing the example code, I tried to upload this to my MSP430FR5969 but I have encountered errors that pertain to the following error:

Error initializing emulator: Could not set device Vcc

For the ADC configuration I tried to fire up the example code on my MSP430 and it crashes it and then gives me the ez FET emulator error. Where it cannot communicate with my MSP430.

I even tried to load the exact example code and load in a 1V pk-pk sine wave. But then when I pause the code to read the values the CPU crashes and then I have to trouble shoot with not having the “updated firmware.”

Any help is appreciated.

Thanks!

Connor Connaughton

0 Bruce McKenney over 5 years ago in reply to Connor Connaughton

Guru 99545 points

1) I'm not sure what the reference to 10 microseconds means. The __delay_cycles(5000) suggests you were aiming for something around 1MHz/5000=200Hz. But since there's other activity in the loop it will be less than that, maybe enough to befuddle the FFT (if you told it 200Hz).

1A) The SHT0 suggestion is independent of the sample rate. If the S/H is too short, you can get things like cross-talk since the sampling capacitor doesn't have time to settle.

2) The TI Examples suite is fairly benign, so I'm not sure how it (in itself) would trigger FET malfunctions. What platform are you using? I just loaded this code on my Launchpad (Rev 2.0) and it functioned as expected. Do you have anything unusual connected?

I'm not familiar with ADC Pro. How does the data get from the MCU to the program (PC)?

0 Mitch Ridgeway over 5 years ago in reply to Bruce McKenney

TI__Expert 6635 points

Hi Connor,

Wanted to check in and see if you were still having issues?

Thanks,

Mitch

0 Mitch Ridgeway over 5 years ago in reply to Mitch Ridgeway

TI__Expert 6635 points

Hey Connor,

I will go ahead and close the thread. If you are still having issues, simply respond to this thread and I will be notified.

Thanks,

Mitch

0 Connor Connaughton over 5 years ago in reply to Mitch Ridgeway

TI__Expert 4470 points

Hi Mitch,

Apologize for the late response. I am not having issues anymore so you may close it.

Thank you,

Connor

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CCS/MSP430FR5969: Using 12b ADC Pro to get correct FFT on ADC Pro

Error initializing emulator: Could not set device Vcc