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[SOLVED] Programming PIC18f4520 to generate 2500Hz Square wave with timer 1

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pravin b

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Hello Friends,
I am Programming PIC18f4520 to generate 2500Hz Square wave with timer 1, no prescaler.
However I have achieved this using following piece of code;
Code: 
void delay()
{
T1CON=0x80;
TMR1L=0x0C;
TMR1H=0xFE;
TMR1ON=1;
while(TMR1IF==0);
TMR1ON=0;
TMR1IF=0;
}

but when I change the above code like;
Code: 
void delay()
{
T1CON=0x80;
TMR1L=0x0C;
TMR1H=0xFE;
TMR1ON=1;
while(TMR1IF==1)
{
TMR1ON=0;
TMR1IF=0;
}
}

some random value of delay is generated; though according to me both the code are same! So I am expecting same output for both the codes i.e. 0.2mses delay or 2500Hz square wave; which is not happening...why?
Please let me know if I am missing something.
Thanks & Regards,
Pravin
 

Look more carefully. The two functions behave very differently. Both codes are NOT the same.

Maybe format your code better and you will see the difference more clearly.

.... or maybe draw a flow chart for each?
 
Notice how the second piece of code doesn't WAIT for the flag to be raised. It checks if the flag is raised and if not, just skips the while loop and returns back to the main code. The first code waits for the flag to be raised - this is the delay you want: to wait until the flag is raised.

Hope this helps.
Tahmid.
 
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