MSP430F2012: Timer goes off every second.....A/D goes off every 5 seconds???

Hi Steve,

Steve Wenner said:

In any event in the TIMERA0_VECTOR if I remove the ...LPM3 line I seem to see a sample every 5 seconds, if I have that line in there I get a sample every 2 seconds??

With the LPM3 line there, you wake up the CPU and execute the code in the while(1) statement immediately after the Timer_A ISR. If pwrDetect = 1, then you change timer modes by modifying TACCTL1 from OUTMOD_5 (reset) to OUTMOD_3 (set/reset).

Without it, you don't wake up and don't execute that code until later and stay in the same mode. Thus, it takes longer for the next interrupt to happen than the previous scenario.

Also, I did want to point out the note at the top of page 358 in the MSP430x2xx Family User's Guide.

It is recommended to stop the timer before modifying its operation (with exception of the interrupt enable, and interrupt flag) to avoid errant operating conditions. When the timer clock is asynchronous to the CPU clock, any read from TAR should occur while the timer is not operating or the results may be unpredictable. Alternatively, the timer may be read multiple times while operating, and a majority vote taken in software to determine the correct reading. Any write to TAR will take effect immediately.

Regards,

James

Hi James...

Not sure I understand what you mean??....I do an ENC (ADC10SC) conversion just before hitting the while loop....After processing AD I wake up THEN the timer interrupt would go off and re-arm the AD converter....The timer is running on VLO (a very slow clock)...The A/D is clocked with 1MHz / 64 for sample+ 13 * 1Mhz for conversion.....I have placed breakpoints and OUTMODE_3 is set correctly and doesn't change (other than from the start of the code and OUTMODE_5)....

I think the issue is in my Timer IRQ....Enalbing the Ref and AD in the same command as ENC and ADC10SC.  I'm basically using up 30us of my sampling time while the reference is unstable

i really don't understand how I move to 5 seconds by NOT waking up after the TIMER_A0 IRQ?  I am in MC_1 (Count up mode and I roll each time)

Thanks

STeve

On further notice....when I run the following line of code:

    ADC10CTL0 |= (ENC + ADC10SC);

BEFORE the while loop, I automatically get a conversion in ADCMEM WITHOUT jumping into my ADC ISR?  How is this possible what is going on?  

The ADC is setup to use MCLK but in LPM3 that doesn't run. Which means that the ADC is only getting clocks while the ISR is running.

Some of the MSP430s have a clock request system that will keep clocks running regardless of low power mode if a peripheral is using it. Perhaps you should be using the ADC10OSC.

David...
Yes I see that in the datasheet however the following coarse code is working....Can you explain this?  Notice...I am in LPM3 and using MCLK for the converter....I have
a large impedance and need a settling time of 80us so the ADC10OSC (5Mhz) i don't believe will cut it (best is /64 divider)....

#include <msp430f2012.h>
#include "LiPo.h"
volatile unsigned int *pBattVolt;

int main(void)
{
  WDTCTL = WDTPW + WDTHOLD;                 // Stop WDT
  pBattVolt = &ADC10MEM;

  BCSCTL3 |= 0x20; BCSCTL1 = CALBC1_1MHZ; DCOCTL = CALDCO_1MHZ;

  P1DIR |= BIT6;  //p1.6 to TA1
  P1SEL |= BIT6;

  TACCR0 = 500;
  TACCR1 = 400;
  TACCTL1 = OUTMOD_3;
  TACTL |= TASSEL_1 | MC_1;
  TACCTL0 |= CCIE;
  TACCTL1 |= CCIE;


  ADC10CTL0 = SREF_1 + REF2_5V + ADC10SHT_3 + REFON + ADC10IE + ADC10ON;
  ADC10CTL1 = INCH_1 + SHS_0 + ADC10DIV_0 + ADC10SSEL_2;
  ADC10AE0 |= 0x02;
  while(1)
  {
    __bis_SR_register(LPM3_bits + GIE);
    if (*pBattVolt > 793)
        TACCTL1 |= (TACCTL1 & ~0x00E0) | OUTMOD_3;
    else
        TACCTL1 |= (TACCTL1 & ~0x00E0) | OUTMOD_5;
  }
}

#pragma vector=TIMERA0_VECTOR
__interrupt void TakeA_D(void)
{
    ADC10CTL0 |= ENC + ADC10SC;
}

#pragma vector=TIMERA1_VECTOR
__interrupt void EnableA_D(void)
{
    switch (TAIV)
    {
    case  2:
        ADC10CTL0 |= REFON + ADC10ON;
        break;
    case  4: break;
    case 10: break;
    default: break;
    }
}


#pragma vector=ADC10_VECTOR
__interrupt void ADC10_ISR(void)
{
  __bic_SR_register_on_exit(LPM3_bits);
}

.....a follow up.....I'm not completely sure here but the above worked. 
I've since revisited what you suggested (thank you btw) and divided down by 5 and it is working ....I'm also able to disable the reference and ADC within the ADC ISR which is great news (with MCLK and before I 
would get ghosting and the ISR wasn't always getting hit)!  My only concern here may be 
stability over temperature but I guess I can live with that.