CCS/MSP430FR5857: Timer

Viswanath

Part Number: MSP430FR5857

Tool/software: Code Composer Studio

My design needs a pin to be low for 5 minutes and then on for 5 secs and want to repeat endlessly. I thought of using the timer for this.

#include <msp430.h>
unsigned int i=1;
int main(void)
{
    WDTCTL = WDTPW | WDTHOLD;               // Stop WDT

    // Configure GPIO
    P1DIR |= BIT2;

    // Disable the GPIO power-on default high-impedance mode to activate
    // previously configured port settings
    PM5CTL0 &= ~LOCKLPM5;

    TA0CCTL0 = CCIE;                        // TACCR0 interrupt enabled
    TA0CCR0 = 50000;
    TA0CTL = TASSEL__SMCLK | MC__CONTINOUS; // SMCLK, continuous mode

    __bis_SR_register(GIE);     // Enter LPM0 w/ interrupt
    __no_operation();                       // For debugger
}

void __attribute__ ((interrupt(TIMER0_A0_VECTOR))) Timer0_A0_ISR (void)
{
    i++;
    if(i%2==0)
    {
        P1OUT |= BIT2;
        TA0CCR0 += 50;
    }
    if(i%2!=0)
    {
        P1OUT &=0xFFFB;
        TA0CCR0 +=65535;
    }
}

This code works but I need a higher off time as I explained above. How can I do that?

Can I use something else other than timer to do the above operation?

Thank you in advance.

Viswanath.

over 8 years ago

0 Clemens Ladisch over 8 years ago

Guru 318700 points

You can use DIVS to make SMCLK up to 32 times slower than the clock source. (The default already divides the 8 MHz source by 8.)
You can use ID and IDEX to make the timer's input clock 64 times slower.

With the default DCOFSEL of about 8 MHz, this would result in a timer tick of 4096 Hz, i.e., the maximum delay would be about 16 s.
If you reduce DCOFSEL, you get a timer tick of 512 Hz, i.e., the maximum delay would be about 128 s.
If you have a 32768 Hz crystal, you can use ACLK instead; the timer tick would be 16 Hz, and the maximum delay, about 4096 s (68 minutes).

Alternatively, don't think of it as a delay of 5 minutes; split it into 20 pieces of 15 s each, and switch the output only after the last one.

0 Viswanath over 8 years ago in reply to Clemens Ladisch

Intellectual 390 points

Thank you Clemens. I am using 16 MHz because I need high speed operation in some parts of the circuit. About the last idea can you just guide me on how to do that.? I mean in terms of code. I am a beginner to ccs and its a little confusing to do it.

0 Clemens Ladisch over 8 years ago in reply to Viswanath

Guru 318700 points

At the moment, your interrupt handler has two states.

The name "i" is meaningless; rename it to "state". Instead of looking at its lowest bit, reset it when it has reached the last state.

Then do whatever is necessary in each state:

switch (state) {
case 0:
    TA0CCR0 += 15000;
    P1OUT |= BIT2;
    break;
case 1:
    TA0CCR0 += 50000;
    P1OUT &= ~BIT2;
    break;
case 2:
case 3:
...
case 20:
    TA0CCR0 += 50000;
    break;
}

state++;
if (state == 21)
    state = 0;

0 Viswanath over 8 years ago in reply to Clemens Ladisch

Intellectual 390 points

Thank you Clemens. I found out another solution for this problem. I used the VLOCLK as my timers clock and then applied the prescalars. Using this we can get a maximum time count of almost 270 minutes.

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CCS/MSP430FR5857: Timer