Is this 38KHz PWM ?

[StefanWxx 2]

Unfortunately I have no osciloscope , is this PWM OK to use it for an IR-Signal?

#include <msp430g2553.h>

void main(void) {

   int counter = 26; // Is this correct?

  WDTCTL = WDTPW + WDTHOLD;        // Stop watchdog timer

  P1DIR |= BIT6;                   // Set P1.6 to output direction
  P1OUT &= ~BIT6;                 // Set the green LED off
  P1SEL |= BIT6;                  // Green LED controlled by PWM

  TA0CCR0 = counter;                // Count limit (16 bit)
  TA0CCR1 = counter/2;              // 50% duty cycle
  TA0CCTL0 = 0x10;                 // Enable Timer A0 interrupts, bit 4=1
  TA0CCTL1 = OUTMOD_7;
TA0CTL = TASSEL_2 + MC_1;        // Timer A0 with ACLK, count UP



  _BIS_SR(LPM0_bits + GIE);        // LPM0 (low power mode) interrupts enabled

}

#pragma vector=TIMER1_A0_VECTOR    // Timer1 A0 interrupt service routine

  __interrupt void Timer1_A0 (void) {

                    // NOOP
}

[Rickta59 589]

yes

[pabigot 355]

Well, maybe. One thing: fix the comment to note that TASSEL_2 means you're actually using SMCLK (nominally 1.1 MHz) instead of ACLK (nominally 12 kHz on that MCU with that initialization sequence).

 

At 1.1MHz I think you'd get 42.3 kHz with 26 ticks per cycle. Since DCO tolerance on the MSP430G2553 is +/- 6% it's probably not very close to 38 kHz.

[oPossum 1,083]

It's close. Can be made more accurate...

 

Set the oscillator to one of the calibrated values.

DCOCTL = 0;
BCSCTL1 = CALBC1_1MHZ;
DCOCTL  = CALDCO_1MHZ;

Set the max count to N - 1

TA0CCR0 = (1000000 / 38000) - 1;
TA0CCR1 = TA0CCR0 >> 1;

[Rickta59 589]

I agree with all of the above. However do you really have to be that accurate for IR?

 

My default clock seems to be 1.012MHz .. so it was 38.0something kHz when I measured it. Of course your results will vary. But for talking talk IR it should be fine.

[RobG 1,892]

Here's another way

DCOCTL |= DCO0 + DCO1; // DCO = ~300kHz
BCSCTL1 |= RSEL0 + RSEL1;
BCSCTL1 &= ~(RSEL2 + RSEL3);
BCSCTL2 |= DIVS0 + DIVS1; // divide SMCLK by 8 which will give ~38kHz

P1DIR |= BIT4; // port 1.4 is configured as SMCLK out and connected to IR emitter, this will be our carrier frequency, 38kHz
P1OUT &= ~BIT4;
P1SEL &= ~BIT4;	// switch carrier off