Re: TPU3 PWM glitch?

Hi Steve,

I've used the PWM function quite a bit, but typically not down to 0
duty cycle, and I've certainly never looked at transitions to zero
carefully. This TPU function has been around a long time, so you'd
think if there was a problem, it would be known and would show up in a
search of TPU threads. Maybe one of the Freescale guys will respond
with a definitive answer. If not, and you have an MIOS pin available,
perhaps the earlier suggestion to use the MIOS instead of the TPU is
the way to go.

Joe

--- In [email protected], "Schroeder, Steven A."
<StevenASchroeder@e...> wrote:
> Just PWMHI.
> 
> Steve
> 
> -----Original Message-----
> From: trailrunner23 [mailto:joep@f...]
> Sent: Wednesday, August 03, 2005 12:52 PM
> To: [email protected]
> Subject: [MPC500] Re: TPU3 PWM glitch?
> 
> 
> According the TPU documentation, you may get a glitch if you request
> an "immediate update" via HSR %01, but if you simply write to PWMHI,
> the duty cycle won't change until the end of the current period and
> you will not get a glitch. The docs say that this should be for 0% or
> 100%. Are you writing to PWHMI and also to HSR to request immediate
> update, or are you simply writing to PWMHI?
> 
> Joe Pasquariello
> 
> --- In [email protected], "Schroeder, Steven A."
> <StevenASchroeder@e...> wrote:
> > We are using a TPU3 channel in the MPC563 to generate a 4kHz PWM
> signal.  Updating the duty cycle is accomplished by simply writing a
> new PWMHI value and it operates very well.  Until now.  When the duty
> cycle first becomes 0% we write 0 to PWMHI.  The first cycle at 0%
> outputs a 550ns pulse; after that it stays low.
> > 
> > The problem is that the device being driven does not like narrow
> pulses such as this.  Has anyone seen this before?
> > 
> > Steve
> > 
> > 
> > [Non-text portions of this message have been removed]
> 
> 
> 
> 
> 
> -----------------------------------------------------------
> To learn more about Freescale Microcontrollers, please visit
> http://www.freescale.com/mcu
> 
> 
>  
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