msp432 duty cycle blink led

Hi Luca!

PWM is more for dimming the LED and not for blinking. But of course a timer is the right module to use for both things. Code examples can be downloaded here.

Dennis

I post my code so you can understand my problem.

// ==========Configuration clock 24Mhz - Smclk 12Mhz==========
CSKEY = 0x695A;                    // Unlock CS module for register access
CSCTL0 = 0;                        // Reset tuning parameters
CSCTL0 = DCORSEL_4;                // Set DCO to 24MHz
CSCTL1 = CSCTL1 & ~(SELS_M | DIVS_M); // Clear existing registers
CSCTL1 = CSCTL1 | (SELS_3 | DIVS_1); // For SMCLK = 12Mhz, select DCO as source then divide by 2
CSKEY = 0;                         // Lock CS module from unintended accesses

// ==========Configurazione ADC 14 bit (12Mhz)==========
P6SEL1 |= BIT1
P6SEL0 |= BIT1;    // p1.6 ad
ADC14CTL0 &= ~ADC14ENC;  //Turn off Enable. With few exceptions, the ADC14 control bits can only be modified when ADC14ENC = 0
ADC14CTL0 = ADC14ON | ADC14SHT0_3 | ADC14CONSEQ_2 | ADC14SSEL_4 | ADC14SHP | ADC14SHS_0;   // Turn on ADC14, set sampling time (SH = 32), repeat single channel (ssel = smclk), adc14sc start
ADC14CTL1 = ADC14RES__14BIT;                      // Use sampling timer, 14-bit conversion results (16 clock cycles)
ADC14MCTL0 = ADC14VRSEL_0 | ADC14INCH_14;         // A0 ADC input select; Vref=AVCC=3.3V
ADC14IER0 |= ADC14IE0;
ADC14CTL0 |= ADC14ENC;                          // ADC enable

// I think total time is: (32 + 16)/12 = 4us < 5us

// ==========Configurazione TimerA0==========
NVIC_ISER0 = 1 << ((INT_TA0_0 - 16) & 31);  // Enable TA0_0 interrupt in NVIC module
TA0CCTL0 &= ~CCIFG;                         // Interrupt disable
TA0CCR0 = 5;                                // Overflow (step dell'interrupt)
TA0CTL = TASSEL__SMCLK | MC__UP | ID_2;     // SMCLK, UP mode, division 4 (12 MHz / 4 = 3 MHz)
TA0EX0 |= TAIDEX_2;                         // division 3 (3 MHz / 3 = 1 MHz)

// ==========Timer A0 interrupt service routin==========
void TimerA0_0IsrHandler(void) {
TA0CCTL0 &= ~CCIFG;
// I want adc sampling only in this period (0-1000). Every 5us i have time to have sample
if(microsecondi > 0 && microsecondi <= 1000) {
    ADC14CTL0 |= ADC14SC; // Start conversion;
    values[index_N] = ADC14MEM0;
    index_N++;
}
microsecondi += 5;
// There is a rtc that repeat this cycle (this works)
if (microsecondi >= 10000){
    microsecondi = 0;
}

I tell you adc because some people suggest me to use PWM (TA0CCR0, TA0CCR1, OUTMOD_X) to have correct sampling at correct frequency. In my code i want assure that adc conversion is only from 0 to 1000 at rate of 1sample/5us for 1000us (200samples). I don't know if this method to use timer ISR and ADC is correct or it is better use PWM or trigger. 

Thanks

From this discussion, this is what I've understood:

You want to take 200 samples in 1mS. Don't you?

In the above case, you can use a timer module to trigger ADC once every 5uS (Be sure to complete ADC reading in < 5uS). You don't have to use PWM.

PWM, is generally used to control the brightness of LED. You can change "Duty Cycle" on a pin, for example, using PWM. So, if you want to dim an LED or control motor speed, you use PWM.

I suggest you go through Timers chapter of this training series. I believe it'll help you deeply understand how timers work. If you've time, kindly complete training series before continuing.

Ok thanks for the timers chapter :). the problem is that i don't find simple examples to trigger ADC with a Timer. With my code i think that i am not sampling every 5us perfectly but 4us (32+16 / 12Mhz) so not 200samples/1ms but 250samples/1ms. If i want sample every 5us (or other) is it better trigger adc with timer?

Can you "Start ADC" (ADC14CTL0 |= ADC14SC) in timer ISR? and read the value after sampling is completed?

Time required for ADC conversion to complete will depend on ADC Clock and ADC14SHT bits. 

Time required will approximately be (16 + SHT)/(ADC Clk Freq.)

Eg: If ADC Clk = 12MHz, SHT = 32, then, (16+32)/(12MHz) = 4uS.

Can you try using faster ADC Clock?

Ok perfect, in fact this calculation is that i use. 

Yes, i can. I could try using adc clock = 24Mhz or 48Mhz (from DCO and then giving to one source clock of adc14).

I have a question: what change to give adc clock faster or slower but keeping the same Time required (16+sht)/(adc clock freq)?? and what change, in terms of quality, use Sht higher or lower?

thanks,

Luca

1. Can you use MODOSC as clock source?

As Ryan Brown1 explained you in earlier discussion, "The sample-and-hold time determines how many cycles the ADC will spend on sampling the signal before it is converted. Smaller values lead to quicker but less dependable/accurate results."

P.S.: The parameters in the example were matched with your parameters intentionally, Sir. :)