msp430 adc interrupt

GURU MOORTHY said:

i want to trigger an adc interrupt in msp430g2553 as soon as the input signal reaches 1.5V. can it be done?

Yes. Using comparator.

can it be done using ADC itself and not using comparator?

GURU MOORTHY said:

can it be done using ADC itself and not using comparator?

No. As far as I know, ADC of msp430 does not have such functionality. Thou you can implement it in software by continuously comparing ADC reading to treshold and then calling function when treshold reached

you can compare analog input with

external reference signal

0,25*Vcc value

0,55*Vcc value

Ilmars said:

No. As far as I know, ADC of msp430 does not have such functionality. Thou you can implement it in software by continuously comparing ADC reading to treshold and then calling function when treshold reached

how can it be done using software comparison. can you just brief?

GURU MOORTHY said:

how can it be done using software comparison. can you just brief?

Sure! http://www.tutorialspoint.com/cprogramming/if_else_statement_in_c.htm

I modyfied TI example for you:

//  If A1 > 1.5V, P1.0 set, else reset.
//
//                MSP430G2x33/G2x53
//             -----------------
//         /|\|              XIN|-
//          | |                 |
//          --|RST          XOUT|-
//            |                 |
//        >---|P1.1/A1      P1.0|-->LED



#include <msp430.h>
#include "intrinsics.h"  

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

  P1DIR |= 0x01;                            // Set P1.0 to output direction

  ADC10CTL0 = SREF_1 + ADC10SHT_2 + REFON + ADC10ON + ADC10IE;               
  ADC10CTL1 = INCH_1;                       // input A1
  ADC10AE0 |= 0x02;                         // PA.1 ADC option select

  __delay_cycles(30000);		    // Delay to allow Ref to settle (30ms)


  __enable_interrupt();  		    // Enable interrupts.

  for (;;)
  {
    ADC10CTL0 |= ENC + ADC10SC;             // Sampling and conversion start
    __bis_SR_register(CPUOFF + GIE);        // LPM0, ADC10_ISR will force exi
    if (ADC10MEM < 0x3ff)                   // ADC10MEM = A1 < 1.5V
      P1OUT &= ~0x01;                       // Clear P1.0 LED off
    else			            // ADC10MEM = A1 > 1.5V			
      P1OUT |= 0x01;                        // Set P1.0 LED on
  }
}

// ADC10 interrupt service routine
#pragma vector=ADC10_VECTOR
__interrupt void ADC10_ISR (void)
{
  __bic_SR_register_on_exit(CPUOFF);        // Clear CPUOFF bit from 0(SR)
}

Ilmars said:

Sure! http://www.tutorialspoint.com/cprogramming/if_else_statement_in_c.htm

This was not I meant. But, thanks

Lukasz said:

  for (;;)
  {
    ADC10CTL0 |= ENC + ADC10SC;             // Sampling and conversion start
    __bis_SR_register(CPUOFF + GIE);        // LPM0, ADC10_ISR will force exi
    if (ADC10MEM < 0x3ff)                   // ADC10MEM = A1 < 1.5V
      P1OUT &= ~0x01;                       // Clear P1.0 LED off
    else			            // ADC10MEM = A1 > 1.5V			
      P1OUT |= 0x01;                        // Set P1.0 LED on
  }
}

// ADC10 interrupt service routine
#pragma vector=ADC10_VECTOR
__interrupt void ADC10_ISR (void)
{
  __bic_SR_register_on_exit(CPUOFF);        // Clear CPUOFF bit from 0(SR)
}

Can you describe the above part. That is when interrupt occurs and what happens inside ISR

GURU MOORTHY said:

what happens inside ISR

When ADC conversions is done and result placed in the ADC10MEM register, ADC interrupt is called. What happens in the ISR is actually said in the comment "Clear CPUOFF bit from 0(SR)" which means upon ISR exit CPU will exit sleep (LPM0 mode), continue execution.

You have another clue in another comment: "ADC10_ISR will force exi"

^^^ exactly

Ilmars said:

When ADC conversions is done and result placed in the ADC10MEM register, ADC interrupt is called. What happens in the ISR is actually said in the comment "Clear CPUOFF bit from 0(SR)" which means upon ISR exit CPU will exit sleep (LPM0 mode), continue execution.

You have another clue in another comment: "ADC10_ISR will force exi"

whether the interrupt occurs for every sample?

Ilmars said:

Yes. Using comparator.

how can we trigger adc interrupt as soon as comparator output goes high?

GURU MOORTHY said:

how can we trigger adc interrupt as soon as comparator output goes high?

Never mind. I was kidding. - What's the point to call ADC interrupt if you already got measurement using comparator?

Solution for your problem is continuous ADC sampling and comparing result to treshold. Lukasz even gave you code sample.

Ilmars said:

Solution for your problem is continuous ADC sampling and comparing result to treshold. Lukasz even gave you code sample.

Can I get ADC interrupt without continuous sampling?

GURU MOORTHY said:

Can I get ADC interrupt without continuous sampling?

Indeed. If you don't like continuous sampling, you can use single conversion mode. Remember that ADC interrupt is "conversion done" interrupt, not like you ask "voltage greater than 1.5V interrupt". If you want ADC that does treshold matching with interrupts in hardware, you shall use another microcontroller with such functionality. Otherwise on msp430 you shall use software solution, as Lukasz advised

p.s. Just curious: GURU is your real name, surname or dignity?

Ilmars said:

p.s. Just curious: GURU is your real name, surname or dignity?

hey,

Gurumoorthy is my real name.

Ilmars said:

Remember that ADC interrupt is "conversion done" interrupt.

So, interrupt is generated after every sample is converted and is written to ADC10MEM or what?

GURU MOORTHY said:

So, interrupt is generated after every sample is converted and is written to ADC10MEM

Yes - if ADC interrupt is enabled. Don't you read User's Guide of chip you use?

Ilmars said:

Yes - if ADC interrupt is enabled. Don't you read User's Guide of chip you use?

I read, but sometimes when I need the clarifications I get into the forum.

Any way, thank you.

The ADC10_A, found in 5x family, has a window comparator that will test the conversion result against an upper and lower limit. The ADC10 of the other families (including the G2xx) doesn’t. So it has to be done anually, by comparing the conversion result against a threshold by software in teh adC ISR.