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.

[infibit]

Ok but I did not understand this statement. Why 13333 and why 2*666

timer_val = 0xFFFF - 13333 + 2*666;

[Håkon Alseth]

13333 = ~20ms, and 666 = ~1ms.

You pulse the pin for 1 ms, which requires one interrupt to set the pin and one to clear the pin. This is in total 2 ms.

To wait a total of 20 ms, you need to set a delay of 20 - 1 - 1 = 18 ms. For the timer itself, this translates to timer val = 13333 - 666 - 666.

 

Kind regards,

Håkon

[infibit]

So if I have to pulse two pins, one for 1ms and the other for 1.5ms using the same timer then what could be the logic? Please give some guidance here..

[Håkon Alseth]

If (0xFFFF - 666) = 1 millisecond, 1.5 millisecond would be (0xFFFF - 1000).

I think you need to sit down and fiddle a bit with your current timer function. You have all what you need in terms of calculations and how the timer works in general to be able to set/clear GPIOs at your wanted intervals.

[infibit]

I wrote this code but it does not work,

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;
  uint16_t timer_val;

	if(timer_state == 2)
  {
    // Need to adjust for the prior timer event
    timer_val = 0xFFFF - 13333 + 4*666;
		P03 = 0;
		P06 = 0;
    timer_state = 0;
  }
	
	if(timer_state == 1)
	{
		timer_val = 0xFFFF-666;
		P03 = 0;
		P06 = 1;
		timer_state = 2;
	}
  if (timer_state == 0)
  {
    timer_val = 0xFFFF - 666;
    P03 = 1;
		P06 = 0;
		timer_state = 1;
  }
  // Wait a given time, in this case 19 ms, before pulsing the pin again.
  
  TL0 = (uint8_t) (timer_val & 0xFF);
  TH0 = (uint8_t) ((timer_val >> 8) & 0xFF);
}

I pulse one pin high for 1ms then I turn it low and pulse  second pin high and then update timer values to 20- 1-1-1-1. Since I am pulsing two pins and 2 ms for each pin.

[Håkon Alseth]

You need to declare "timer_state" with a static uint8_t, instead of static bit. "bit" is a boolean type in 8051, and cannot be 2.

 

Kind regards,

Håkon

[infibit]

Yeah found that and corrected it...now it is working.. Thanks for your valuable support....