56803 PWM duty cycle sweep speed

Started by Corey, Rick June 14, 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



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



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


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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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



Create like a god,Command like a king,Work like a slave
---------------------------------
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Infineon technologies Pvt.Ltd
10th Floor,Discoverer Building
International Tech Park
Bangalore 560066.
 
Tel: +91 80-51392055
---------------------------------

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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



Create like a god,Command like a king,Work like a slave
---------------------------------
R.Christober
Infineon technologies Pvt.Ltd
10th Floor,Discoverer Building
International Tech Park
Bangalore 560066.
 
Tel: +91 80-51392055
---------------------------------

Yahoo! India Matrimony: Find your partner online.

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



_____________________________________
Note: If you do a simple "reply" with your email client, only the author of this message will receive your answer.  You need to do a "reply all" if you want your answer to be distributed to the entire group.

_____________________________________
About this discussion group:

To Join:  m...@yahoogroups.com

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Archives: http://www.yahoogroups.com/group/motoroladsp

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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


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



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