making a pulse of 2 ms using timer in pic 18f452

its not generating pulses of 2 ms am i doing something wrong here? is the code right?

---------- Post added at 21:00 ---------- Previous post was at 20:59 ----------

the oscillators frequency is taken as 10 MHz

---------- Post added at 21:21 ---------- Previous post was at 21:00 ----------

FFFFh-FFB2h=4Dh=77+1=78
78*64*0.4 us=1996.8 us=2 ms

---------- Post added at 21:22 ---------- Previous post was at 21:21 ----------

the prescale is 1:64 as T0CON=0x05 = 00000101

linkstatic said:

Code:

#pragma config OSC=HS,OSCS=ON
#pragma config WDT=OFF
#pragma config PWRT=ON,BOR=ON,BORV=45

#include<P18F452.h>
#define mybit PORTBbits.RB4
void delay(void);

void main()

{
TRISBbits.TRISB4=0;
while(1)
  {
mybit^=1;

delay();
}




}

void delay(void)
{
T0CON=0x05;
TMR0H=0xFF;
TMR0L=0xB2;
T0CONbits.TMR0ON=1;
while(INTCONbits.TMR0IF==0);
T0CONbits.TMR0ON=0;
INTCONbits.TMR0IF=0;
}

its not generating pulses of 2 ms am i doing something wrong here? is the code right?

---------- Post added at 21:00 ---------- Previous post was at 20:59 ----------

the oscillators frequency is taken as 10 MHz

---------- Post added at 21:21 ---------- Previous post was at 21:00 ----------

FFFFh-FFB2h=4Dh=77+1=78
78*64*0.4 us=1996.8 us=2 ms

---------- Post added at 21:22 ---------- Previous post was at 21:21 ----------

the prescale is 1:64 as T0CON=0x05 = 00000101

Click to expand...

Apart from crystal frequency and prescaler factor, another factor in the delay size is the C compiler . :-D

so i can never get a 2 ms pwm? i need to run a servo

This website allows you to enter your PWM frequency and it will generate all the necessary code to initialise the PWM module for you.

http://www.micro-examples.com/public/microex-navig/doc/097-pwm-calculator.html

Or there is this website for generating the timer frequency.

**broken link removed**

In terms of your code above, what is the output actually doing, is it pulsing?
Do you actually need to use the timer to generate this delay because as your arent using interrupts your are still just burning CPU cycles waiting for the interrupt flag to be set, could you not use the delays.h library which takes the clock speed into acount and gives you accurate delays?

Hope this helps.

/Pheetuz

linkstatic said:

so i can never get a 2 ms pwm? i need to run a servo

Click to expand...

Various C compilers generate different hex code sizes. You can verify the actual delay with an oscilloscope.

linkstatic said:

so i can never get a 2 ms pwm? i need to run a servo

Click to expand...

2ms in microprocessor terms is an age, you will be able to get pretty damn close to 2mS, essentially to within one instruction cycle depending on your code.