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Hi! I have written the code for software PWM whose PWM frequency is 20KHz
Method: 1) Generate PWM1 and PWM2 of 20KHz frequency using PWM command 2) wait for TMR2 to PR2 match interrupt Flag 3) when this flag=1 then high PWM3 port pin and start timer1 whose max delay is 50usec (20KHz)
but for 50% Duty Cycle I have reduce Timer1 delay to 25Usec by setting its TMR1H and TMR1L variables and jump to Step '1'
When Timer1 OV interrupt generated then i have low PWM3 Port Pin so its frequency is equal to 20Khz but i have received 0.146V on PWM3 port pin instead of 2.5V and it is not working correctly , i have also attached the code if anybody find the mistake then it will be highly appreciated
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C:\\documents and setings\\mandeep\\my projects\\PWM.txt (7.56 GB)
Neither sure of language nor chip.
Looks like some kind of BASIC...?
I don't have you COMPILER install in my computer so I can not compile your program. But I see one could be mistake in your program.
In the data sheet it said:
"The prescaler counter is cleared on writes to the TMR1H or TMR1L registers".
It could be true because your duty cycle now is only 12.4uS instead of 49.6uS. Which mean the LED on time is 1/4 of what you have planned.
So in your TMR1_ISR, after you write new value into timer1, set bits for prescale too.
TMR1_ISR: LOW PWM3 LOW led timer1=65473 '(50% DUTY CYCLE of 50US=25usec)
T1CKPS0=1 ' set prescale bits for 1:4 T1CKPS1=0 ' set prescale bits
TMR1=0 REGISTER RESTORE
Also, in the data sheet said: "For writes, it is recommended that the user simply stop the timer and write the desired values. A write contention may occur by writing to the timer registers, while the register is incrementing. This may produce an unpredictable value in the timer register". I doubt it would help???
In this line:
SYMBOL FTMR1 = PIr1.0 ' TIMER1 OVERFLOW FLAG
Is PIr ok with your compiler? I don't know if its case sensitive.
Tom
The unknown compiler may or may not be - but the symbols for SI units certainly are!
"your duty cycle now is only 12.4uS (sic) instead of 49.6uS (sic)"
The symbol for seconds is a lowercase 's'; An uppercase 'S' means siemens - the unit of conductance (reciprocal of resistance).