CCS/MSP430F5529: Using PWM and built-in timers to fade LED

Paul Mitchell

Part Number: MSP430F5529

Tool/software: Code Composer Studio

I am trying to use Timer_A to operate a fading LED with PWM. This is my first time using the timers on this board, and I am having an issue getting this to work. Can you guys tell me what I am doing wrong? Thank you for your time in advance. Here is my code thus far:

#include <msp430.h>

void _delay_ms(volatile unsigned int length){
    volatile unsigned int delay = 0;
    for(delay = 0; delay < length; delay++){
        _delay_cycles(1000);
    }
}

int main(void){

    WDTCTL = WDTPW + WDTHOLD;                 // Stop watchdog timer

    P1DIR |= BIT0;
    P1SEL |= BIT0;

    TA0CCR0 = 1000-1;
    TA0CCTL1 = OUTMOD_7;
    TA0CCR1 = 0;

    TA0CTL = TASSEL_1 + MC_1;

    volatile signed int i = 0;

    while(1){

        for(i = 1; i < 999; i += 10){
            TA0CCR1 = i;
            _delay_ms(10);
        }

        for(i = 999-1; i > 0; i -= 10){
            TA0CCR1 = i;
            _delay_ms(10);
        }
    }
}

over 4 years ago

0 Bruce McKenney over 4 years ago

Guru 99415 points

1) You're programming TA0.1, but that's over on P1.2, not P1.0. [Ref data sheet (SLAS590N) Table 6-46]. The simplest fix is probably to add "P1SEL |= BIT2;" and jumper JP8 (LED side) to the P1.2 pin.

2) Your PWM period is 1000/32768=30.5ms, so you're changing CCR1 three times each cycle. This will sort-of work but you may see glitches. I suggest setting CCR0=32768/100=328 (10ms delay->100Hz).

[Edit: Added reference.]

0 Paul Mitchell over 4 years ago in reply to Bruce McKenney

Intellectual 510 points

That was good advice, thank you! I have updated my code as follows and jumpered JP8 to P1.2:

#include <msp430.h>

void _delay_ms(volatile unsigned int length){
    volatile unsigned int delay = 0;
    for(delay = 0; delay < length; delay++){
        _delay_cycles(1000);
    }
}

int main(void){

    WDTCTL = WDTPW + WDTHOLD;                 // Stop watchdog timer

    P1DIR |= BIT2;
    P1SEL |= BIT2;

    TA0CCR0 = 350;
    TA0CCTL1 = OUTMOD_7;
    TA0CCR1 = 0;

    TA0CTL = TASSEL_1 + MC_1;

    volatile signed int i = 0;

    while(1){

        for(i = 1; i < 309; i += 5){
            TA0CCR1 = i;
            _delay_ms(50);
        }

        for(i = 309-1; i > 0; i -= 5){
            TA0CCR1 = i;
            _delay_ms(50);
        }
    }
}

These changes have made it so I get a smooth fade in that takes almost exactly 3s followed by a smooth fade out that takes almost exaclty 3s. Thank you very much for your help.

0 Paul Mitchell over 4 years ago in reply to Paul Mitchell

Intellectual 510 points

I will note that I occasionally see a little flicker in the LED. I am not sure what causes this.

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CCS/MSP430F5529: Using PWM and built-in timers to fade LED