MSP430G2553 Timer Intervals

Question

After reading the text about five times and googling I've decided to reach out for help. I'm currently in the process of using Timer_A interrupt to turn on/off two LEDS in intervals of 1 second/10 seconds/1 minute one at a time. The default program will turn on/off the LEDS every second but I cannot find a way to turn them off after 10 seconds and a minute. I can use __delay_cycles(xxxx) to achieve this but apparently doing so would defeat the purpose of the timer. This is my code.

#include <msp430.h>

#define RedLED BIT0
#define GreenLED BIT6

#define RedLEDToggle (P1OUT ^= RedLED)
#define GreenLEDToggle (P1OUT ^= GreenLED)

unsigned int counter = 0;


void main(void)
{
    WDTCTL = WDTPW | WDTHOLD;
    //WDTCTL = WDT_MDLY_32;

    P1DIR = RedLED | GreenLED;
    P1OUT = RedLED | GreenLED;

    TACTL = TASSEL_2 | ID_3 | MC_3 | TAIE;

    TACCR0 = 62500;

    _enable_interrupts();


    LPM1;
}

#pragma vector=TIMER0_A1_VECTOR

__interrupt void Timer_A(void)
{

if ( counter == 10)
{
switch (TAIV)
    {
    case 0x02: break;
    case 0x04: break;
    case 0x0A: RedLEDToggle | GreenLEDToggle;
        break;
    }
}
else
{
counter ++;
}       
}

Answer 1

To achieve 10 second interrupt interval, you need to apply input divider to the timer. It is not possible to achieve 1 minute without peripheral support (see the other answers on how to implement that with a software counter).

The problem is that msp430 microcontrollers have 16-bit registers, not capable of holding numerical values larger than 65535. Using low-frequency oscillator running at 32768 Hz (as is typical - you don't provide any details about the hardware clock sources of your system, if they have a different frequency, please mention that) the register overflows once every 2 seconds unless an input divider is applied. The maximum value of input divider on MSP430x2xxx family MCUs is 8, so it's not possible to set a hardware timer more than 8 * 2 = 16 seconds in the future. Refer to MSP430x2xxx family user's guide for further details.

This code calls the interrupt once 10 seconds:

#include <msp430.h>

#define RedLED BIT0
#define GreenLED BIT6

#define RedLEDToggle (P1OUT ^= RedLED)
#define GreenLEDToggle (P1OUT ^= GreenLED)

// 10 seconds, assuming 32768 Hz ACLK source and divider 8
#define TIMER_PERIOD (10u * (32768 / 8))

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

    P1DIR = RedLED | GreenLED;
    P1OUT = RedLED | GreenLED;

    // reset timer A config (not strictly needed)
    TACTL = TACLR;

    // ACLK as clock source, divider 8, continuous mode, interrupt enabled
    TACTL = TASSEL_1 | ID_3 | MC_2 | TAIE;

    // set the period
    TACCR1 = TIMER_PERIOD;

    // enable capture/compare interrupts for CCR1
    TACCTL1 = CCIE;

    _enable_interrupts();

    LPM1;
}

#pragma vector=TIMER0_A1_VECTOR

__interrupt void Timer_A(void)
{
    switch (TAIV) {
    case 0x02:
        // CCR1 interrupt
        RedLEDToggle;
        GreenLEDToggle;
        // set the time of the next interrupt
        TACCR1 += TIMER_PERIOD;
        break;
    }
}