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Heliophagus
Joined: 30 Oct 2008
Posts: 4
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| Maximum 8-channel PWM frequency? |
 Posted: Thu Oct 30, 2008 10:23 am |
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Greetings! New member with an odd question.
I need 8 PWM channels, 10-bit resolution, preferably using a single PIC. Using a very simple algorithm, such as | Code: |
int16 LoopCount = 0;
while (true)
{
output_bit(Pin_B0,(PWM1 < LoopCount))
output_bit(Pin_B1,(PWM2 < LoopCount))
// etc.
++LoopCount
LoopCount%=1024
}
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...on a PIC18F2523 using a 32 MHz clock I get nice PWM, but the repetition frequency is only about 100 Hz. Ideally I'd like it to be much, much faster (ultrasonic if possible). Does anyone have any suggestions for a better algorithm, or might it be necessary to use multiple PICs with their two hardware PWMs each? Or a 16-bit PIC?
Any helpful suggestions would be greatly appreciated. |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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John P
Joined: 17 Sep 2003
Posts: 331
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| Posted: Thu Oct 30, 2008 4:14 pm |
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It seems clear that if you want a 10-bit resolution, you'd have a frequency of 1024 * the instruction time, or about 8KHz. If that's not fast enough, then you need to look elsewhere for a processor.
I can't imagine a scheme which would allow you to change outputs in an arbitrary pattern, with only one instruction time between successsive changes. Even a broadside load of the output port would take two instructions.
Suppose the requirement is that at time 0, all the outputs go on, then at time 1, output 0 and output 1 go off, at time 2 outputs 2 and 3 go off and so forth. If there's a way to do this, even if the pattern never changed, I can't see how it could work. |
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