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NRF24LE1 how to set PWM frequency?

infibit

To what values should I set the PWMCON register to so that the PWM0 and PWM1 frequency is output at 20Khz with duty cycle varying between 1 to 2ms. Now specifically I am asking this after reading the data sheet because the tables mentioned are not clearing giving information. How do I decipher the table given here:

Please clearly disclose information in the data sheets. Also give an example to show how to set to particular frequency and pulse width.

Let me tell you how I decipher this as a newbie. Now CCLK is 16,000,000 for 16Mhz clock. I chose PWM0 as output so bit 0 is 1 and bit 1 is 0. Now I need to find out what PWMCON is so the formula for PWMCON for 20Khz PWM freq will be. (16000000/(255 x 20000))-1 = 160/51 -1 which is approximately 2. Hence PWMCON[5:2] will be 0010. There fore PWMCON will be 11001001 which is 0xC9. But this dint work when I put in this value for PWMCON as the servo did not rotate. Here is my code.

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#include "reg24le1.h" // I/O header file for NRF24LE1
#include "hal_delay.h" // header file containing delay functions
// main function
void main()
{
int i = 0, j = 0; // loop variable
P0DIR = 0; // Port 0 as output
PWMCON = 0xc9; // enable PWM1
// infinte loop
while(1)
{
for(i= 180; i--; i > 0)
{
PWMDC0 = i ; // change duty cycle
delay_ms(10); // delay of 10 ms
}
}
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

Parents
  • 0

    How do we get a 50Hz PWM wave? What changes should I make to the code.

  • 0 in reply to infibit

    It does not go that far down. From the documentation:

    The following table shows how the PWM frequency (or period length) and the PWM duty cycle are controlled
    by the PWM SFR registers. PWM frequency range is approximately 4 kHz-254 kHz.

  • 0 in reply to Håkon Alseth

    Why do your waves always have 50% duty cycle? I am waiting for your reply. I posted more queries and some oscilloscope shots.

  • 0 in reply to Håkon Alseth

    I will try to modify my own AVR code for this and develop a library. I need you to tell the equivalent statements for the timers in NRF24LE1.

    1st section of code

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    void servoStart(void)
    {
    // Outputs
    //if(servouniv<=7)
    SERVO_DDR |= SERVO_MASK;
    //if(servouniv>7 && servouniv<=15)
    SERVO_DDR1 |= SERVO_MASK;
    // Setupt a first compare match
    OCR1A = TCNT1 + US2TIMER1(100);
    // start timer 1 with no prescaler
    TCCR1B = (1 << CS10);
    // Enable interrupt
    TIMSK |= (1 << OCIE1A);
    }
    XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

    2nd section of code

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    ISR(TIMER1_COMPA_vect)
    {
    static uint16_t nextStart;
    static int servo=-1;
    static uint8_t servo1;
    static bool outputHigh = true;
    uint16_t currentTime = OCR1A;
    uint8_t mask = servoOutMask[servo];
    // uint8_t mask1 = servoOutMask1[servo];
    servouniv=servo;
    if (outputHigh)
    {
    if(servo>=6)
    SERVO_PORT1|= mask;
    if(servo<=5)
    SERVO_PORT |= mask;
    XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

    Please let me know the equivalent statements

  • 0 in reply to Håkon Alseth

    For the first section of the code I did this.

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    // Setupt a first compare match
    //OCR1A = TCNT1 + US2TIMER1(100);
    short combined = (TH1 << 8 )| TL1;
    //CC1S = (CCH1 << 8) | CCL2;
    short CC1S = combined + US2TIMER1(100);
    // start timer 1 with no prescaler
    //TCCR1B = (1 << CS10);
    TR0 = 1;
    // Enable interrupt
    //TIMSK |= (1 << OCIE1A);
    ET0 = 1;
    XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

    Is this right?

  • 0 in reply to infibit

    Hi,

     

    If you want to generate a 1 ms pulse then wait 20 ms, you can do something like this in your ISR routine:

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    void t0_interrupt(void) interrupt 1
    {
    // Timer increments every 2*12 CPU clock cycles
    // Timer starts counting down from 65535
    // 666 * 1,5 us = 999 us
    static bit timer_state;
    static bit gpio_is_set;
    uint16_t timer_val;
    if (timer_state == false)
    {
    timer_val = 0xFFFF - 666;
    if (gpio_is_set == 1)
    {
    timer_state = true;
    }
    gpio_is_set ^=1;
    P10 ^= 1;
    }
    // Wait a given time, in this case 19 ms, before pulsing the pin again.
    XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

    You need to set the LED, wait x ms, then turn it off. Then you extend the timer to be 18 ms (20 ms total), then re-do the whole procedure.

    Could you try that?

     

    Kind regards,

    Håkon

  • 0 in reply to Håkon Alseth

    If I have to control two servos with a single timer then how do I do that? Please let me know. I am trying to get a second servo working. Now the pulse width for both of the servos should be unique so that I can hold these servos at independent angles..

Reply
  • 0 in reply to Håkon Alseth

    If I have to control two servos with a single timer then how do I do that? Please let me know. I am trying to get a second servo working. Now the pulse width for both of the servos should be unique so that I can hold these servos at independent angles..

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