missing pwm signal in msp430g2553 in up/down mode

Dear Ilmars

Can you please show some sample codes how to update that pwm values in timer interrupt of TAIF. how can we synchronize timer speed with cpu speed for the pwm update.

Hi Sun!

Have a look at this example:

It is for the MSP430G2553 and uses the timer module's hardware PWM. The update for the new duty-cycle happens when TAIFG causes an interrupt.

Dennis

SUN POST said:

unsigned int const pwm[10]=={0, 31, 59, 81, 95, 100, 95, 81, 59, 31};

Doesn't the compiler complain about this line?

If you want to assign something you use the single '='. You use the double '==' to compare the value.

Additionally you should change your comments to match the code, otherwise it is misleading because one cannot say if you want the code to do to what the code lines say, or if you wanted the code to behave like mentioned in the comments, but you just did it wrong.

#include "msp430G2553.h"
#include <stdint.h>

unsigned int const pwm[10] == {0, 31, 59, 81, 95, 100, 95, 81, 59, 31}; // < ERROR: USE '=' INSTEAD OF '=='
unsigned int index = 0;

void main( void )
{
  WDTCTL = (WDTPW | WDTHOLD);                       // Stop watchdog timer

  BCSCTL1 = CALBC1_16MHZ;                           // Set range to 8MHz                                    < WRONG
  DCOCTL = CALDCO_16MHZ;                            // Set DCO step and modulation to 8MHz                  < WRONG

  P1SEL = 0x40;                                     // Set special function of P1.6 (LED2) to timer module
  P1DIR = 0x40;                                     // Set P1.6 (LED2) to output direction

  TA0CCR0 = (125 - 1);                              // Frequency 10kHz                                      < WRONG
  TA0CCR1 = 0;                                      // Duty cycle 5%                                        < WRONG
  TA0CCTL1 = OUTMOD_6;                              // Reset / set                                          < WRONG
  TA0CTL = (TASSEL_2 | ID_0 | MC_3 | TACLR | TAIE); // SMCLK, divider 1, up-mode, clear, interrupt enabled  < WRONG

  _BIS_SR( GIE );                                   // Enable global interrupts

  while( 1 );                                       // Endless loop
}

Dennis

Dear Dennis,

Please check the file.

Thanks.

Sun,

do you have to use the up/down mode for PWM generation? If yes, then did you already look at the code examples for the MSP430G2553 processor? You can download them here and they also contain one example about the up/down mode PWM generation:

• msp430g2xx3_ta_19.c                        Timer_A, PWM TA1, Up/Down Mode, DCO SMCLK

Then having a second look at the user's guide may not the worst idea. You find it here, chapter 12 is about the timer. There are graphs that show the timer's operation in it's different modes - for up/down mode it looks like this:

Maybe you explain in detail what you expect from your program. What shall it do?

Dennis

Dear Dennis,

This is the thing that i asked in the starting can you help me to trace why the pwm having unwanted width i already send the code and wave form to you. i am again attaching the same for your reference. this is the code

#include "msp430G2553.h"

#include <stdint.h>

unsigned int const pwm[10]={0, 31, 59, 81, 95, 100, 95, 81, 59, 31};

unsigned int index=0;

void main( void )

{

WDTCTL = (WDTPW | WDTHOLD);

BCSCTL1 = CALBC1_16MHZ;

DCOCTL = CALDCO_16MHZ;

P1SEL = 0x40;

P1DIR = 0x40;

TA0CCR0 = (125 - 1);

TA0CCR1 = 0;

TA0CCTL1 = OUTMOD_6;

TA0CTL = (TASSEL_2 | ID_0 | MC_3 | TACLR | TAIE);

_BIS_SR( GIE );

while( 1 );

}

// Timer0 A1 interrupt service routine

#pragma vector = TIMER0_A1_VECTOR

__interrupt void Timer0_A1_ISR( void )

{

static int duty = 0;

TA0CTL &= ~TAIFG;

if (index < 10)

{

duty = pwm[index];

index++;

}

else

{

duty = pwm[0];

index = 1;

}

TA0CCR1 = duty;

}

and this is the scope out. please advise.

thanks.

Dear Dennis,

Please look the output wave form. my pwm values are 0, 31, 59, 81, 95, 100, 95, 81, 59, 31 but the wave form is having some unwanted widths.

thanks.

Hi Sun!

SUN POST said:

but the wave form is having some unwanted widths.

So which of the widths are correct and which are not? The processor does what you tell him, so you should explain what it shall look like.

Dennis

Dear Dennis,

Please have a look on the image the arrow mark shows the unwanted PWM

Thanks.

If I were you I would test it to know for sure.

In your code, the timer generated interrupts too often and the CPU cannot handle them in time. The resulting waveform at P1.6 is difficult to predict.

I slowed down the timer clock by a factor of 8x8=64. The result looks fine to me (but may not what you expect).

#include "msp430G2553.h"
#include <stdint.h>

unsigned int const pwm[10]={0, 31, 59, 81, 95, 100, 95, 81, 59, 31};
unsigned int index=0;

void main( void )
{
WDTCTL = (WDTPW | WDTHOLD);

DCOCTL = CALDCO_16MHZ;                                      //swap these 2 lines  
BCSCTL1 = CALBC1_16MHZ;                                     //for safer clocking
BCSCTL2 = DIVS_3;                                           //SMCLK is DCO/8


P1SEL = 0x40;
P1DIR = 0x40;

TA0CCR0 = (125 - 1);
TA0CCR1 = 0;
TA0CCTL1 = OUTMOD_6;
TA0CTL = (TASSEL_2 | ID_3 | MC_3 | TACLR | TAIE);           //clock by SMCLK/8

_BIS_SR( GIE );

while( 1 );
}

// Timer0 A1 interrupt service routine
#pragma vector = TIMER0_A1_VECTOR
__interrupt void Timer0_A1_ISR( void )
{
static int duty = 0;
TA0CTL &= ~TAIFG;
if (index < 10)
{
duty = pwm[index];
index++;
}
else
{
duty = pwm[0];
index = 1;
}
TA0CCR1 = duty;
}