PWM duty cycle as a percentage.

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Suraj143

Active Member

• Jan 3, 2008

• #1

In an eight bit register I’m turning ON a bit 100 times & the other 155 balance I’m turning OFF.
So how can I tell this as a percentage I mean the duty cycle?

Thanks

 

K

kchriste

New Member

Forum Supporter

• Jan 3, 2008

• #2

It is approximately 39% duty cycle. (It should really be 100 and 156 for a total of 256 states) 100 / (100+156) = 39.06%

 

S

Suraj143

Active Member

• Jan 3, 2008

• #3

Oh thank you very much kchriste now I understood.

Is there any frequency in my application?Is it 256?

 

K

kchriste

New Member

Forum Supporter

• Jan 3, 2008

• #4

Is there any frequency in my application?

Click to expand...

Yes. I assume you are using a PIC (From your other posts). The PWM frequency depends on the PICs clock frequency and the values in the PR2 and T2CON registers. From a datasheet:
PWM period = [(PR2) + 1] * 4 * TOSC * (TMR2 prescale value)
PWM frequency = 1 / PWM period.

 

S

Suraj143

Active Member

• Jan 3, 2008

• #5

Oh I see I have to study that a little bit.

But in my application i'm not using any Timers its just a basic software type one.Incrementing a register 100 times while the bit is turned ON & the other balance counting upto 256 while the bit turns OFF.

My XT is 4mhz.In this situation how to tell the frequency?

 

Last edited: Jan 3, 2008

geko

Active Member

• Jan 4, 2008

• #6

My XT is 4mhz.In this situation how to tell the frequency?

Click to expand...

Run the code in MPLAB simulator for one on/off cycle. That will tell you how long it took. Then just use 1/cycle_time for the frequency.