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Discussion Groups | Freescale DSPs | 56803 PWM duty cycle sweep speed


Technical discussions about Freescale (Motorola) DSPs (including the DSP56000, DSP56300, DSP56600, 56800 DSPs).

  

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56803 PWM duty cycle sweep speed - Corey, Rick - Jun 14 20:11:00 2004

Hi

We are presently trying to use the DSP56F803 PWM (channel 4) as a simple
independent PWM output. We are sweeping the output duty cycle from 0% to
100% and therefore, updating and reloading the PWM timer on every timeout
interrupt of the PWM.

When we then observe the PWM output on a scope, the rate at which the PWM
duty cycle is changing, is taking much longer then we would expect (4 to 5
sec to go from 0 to 100 % duty cycle).

We have also seen that the rate at which this output duty cycle can be
changed is somehow tied to the configured base frequency of the PWM.

Is this normal operation as per the 56803 implementation of the PWM
functionality?
Has anyone gotten the duty cycle to change faster?

The prescaler and modulus are set for PWM freq = 4.32khz.

We expected the duty cycle to change in microseconds or milliseconds, not
seconds.

Thanks

Mike Kertesz







56803 PWM duty cycle sweep speed - Corey, Rick - Jun 14 20:14:00 2004

Hi

We are presently trying to use the DSP56F803 PWM (channel 4) as a simple
independent PWM output. We are sweeping the output duty cycle from 0% to
100% and therefore, updating and reloading the PWM timer on every timeout
interrupt of the PWM.

When we then observe the PWM output on a scope, the rate at which the PWM
duty cycle is changing, is taking much longer then we would expect (4 to 5
sec to go from 0 to 100 % duty cycle).

We have also seen that the rate at which this output duty cycle can be
changed is somehow tied to the configured base frequency of the PWM.

Is this normal operation as per the 56803 implementation of the PWM
functionality?
Has anyone gotten the duty cycle to change faster?

The prescaler and modulus are set for PWM freq = 4.32khz.

We expected the duty cycle to change in microseconds or milliseconds, not
seconds.

Thanks

Mike Kertesz







56803 PWM duty cycle sweep speed - Corey, Rick - Jun 14 20:18:00 2004

Hello

We are presently trying to use the DSP56F803 PWM (channel 4) as a simple
independent PWM output. We are sweeping the output duty cycle from 0% to
100% and therefore, updating and reloading the PWM timer on every timeout
interrupt of the PWM.

When we then observe the PWM output on a scope, the rate at which the PWM
duty cycle is changing, is taking much longer then we would expect (4 to 5
sec to go from 0 to 100 % duty cycle).

We have also seen that the rate at which this output duty cycle can be
changed is somehow tied to the configured base frequency of the PWM.

Is this normal operation as per the 56803 implementation of the PWM
functionality?
Has anyone gotten the duty cycle to change faster?

The prescaler and modulus are set for PWM freq = 4.32khz.

We expected the duty cycle to change in microseconds or milliseconds, not
seconds.

Thanks

Mike Kertesz






Re: 56803 PWM duty cycle sweep speed - Douglas Holub - Jun 14 21:33:00 2004

The PWM duty cycle can only be changed at PWM period intervals. You can write to the value registers any time, but they only take effect at the beginning of the next PWM period.  So at 4.32 kHz, the PWM duty cycle can only be changed every 231 usecs.  If you have 16-bits of resolution, and you change the duty cycle one count at a time, it will take (231 usecs * 65535) = 15.17 seconds to sweep from 0 to 65535.  If you have 15-bits of resolution, it will take 7.59 seconds, etc.
 
Doug Holub
----- Original Message -----
From: Corey, Rick
To: 'm...@yahoogroups.com'
Sent: Monday, June 14, 2004 3:18 PM
Subject: [motoroladsp] 56803 PWM duty cycle sweep speed

Hello

We are presently trying to use the DSP56F803 PWM (channel 4) as a simple
independent PWM output. We are sweeping the output duty cycle from 0% to
100% and therefore, updating and reloading the PWM timer on every timeout
interrupt of the PWM.

When we then observe the PWM output on a scope, the rate at which the PWM
duty cycle is changing, is taking much longer then we would expect (4 to 5
sec to go from 0 to 100 % duty cycle).

We have also seen that the rate at which this output duty cycle can be
changed is somehow tied to the configured base frequency of the PWM.

Is this normal operation as per the 56803 implementation of the PWM
functionality?
Has anyone gotten the duty cycle to change faster?

The prescaler and modulus are set for PWM freq = 4.32khz.

We expected the duty cycle to change in microseconds or milliseconds, not
seconds.

Thanks

Mike Kertesz
M...@dpconline.com



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reg:block convolution - Christ - Jun 15 6:28:00 2004

HI,

whether anyone has worked with block convolution ? can u tell the link in which the algorithm is given in detail?.i am implementing an optimum compiler for convolution.

              ;       thanks

              ;         chris



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