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.

#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
}
 
 
}
 
}

[infibit]

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

[Håkon Alseth]

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.

[Håkon Alseth]

Hi,

 

Did you scope the correct pin? P1.0 should toggle in the example I posted.

Here's the logic analyzer trace:

Kind regards,

Håkon

[infibit]

Yes, I scoped the pin and was able to see the PWM signal. I was also able to adjust to pulse width. But how do I change the frequency of the wave? Like if I want to change from 50Hz to 20Hz what parts of the code do I need to change? Which numbers do I need to change? What I found that the arduino is putting out a PWM signal at much less frequency like around 20Hz. Now how do I change the PWM generated by your code from 50Hz to 20Hz. Please explain the calculation.

How are you arriving at these numbers (as mentioned in your code)?

 // Timer increments every 2*12 CPU clock cycles    
  // Timer starts counting down from 65535
  // 6666 * 1,5 us = 9999 us

[Håkon Alseth]

Each tick is CPU_CLOCK / 12*2 = 1,5 us per tick. Timer starts decrementing from 0xFFFF and down.

That gives (for 50 Hz):

10000 us = x * 1,5, x = 10000/1,5.

timer_val = 0xFFFF - 6666.

If you want 20 Hz, you need to adjust the above value to match 1/ 2*(20 Hz), as you want to toggle the GPIO two times to generate the signal.

Best regards,

Håkon

[infibit]

So for 50 Hz you took 10000us so for 20Hz it would be 25000us. Therefore X will be 25000/1.5 = 16,666. But now how do I get a PWM or 1 to 2milli second pulse width here in 20Hz wave? Please let me know. Again the pulse width of 1ms to 2ms calculation at 20Hz is not clear to me. Please let me know the exact numbers..

[infibit]

The above signal is the arduino servo signal on which the servo works.

The below signal is from the NRF24LE1 from the code you provided. It always appears that the duty cycle is 50%. How do I get it to 1 to 2ms Pulse width at 20 Hz frequency. Are you able to read the frequency of the the above signal?

Give above is the NRF24LE1 PWM signal and it appears that the duty cycle is always 50%. Why?