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delay_ms() issues - being shorted on time!

 
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SuperAlpha



Joined: 19 Apr 2007
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delay_ms() issues - being shorted on time!
PostPosted: Wed May 09, 2007 8:06 am     Reply with quote

Hi.
I am using the built-in delay function and it does not work as advertised. Interrupts are not disabled so I expect the delay to be "at least" 20ms. The clock is 20MHz as measured and serial communications function well.
The delay varies from 16.0ms to 17.5ms, but never >=20.0ms.

Does anybody know what could be wrong here? I want to avoid making my own version of a delay loop, if possible.

#pragma use delay(clock=20M, ocillator, restart_wdt)
delay_ms(20);



Thanks
ckielstra



Joined: 18 Mar 2004
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PostPosted: Wed May 09, 2007 9:09 am     Reply with quote

I'm not aware of any problems with the delay_ms() function. Which compiler version are you using?

The code as posted has some typing errors in it. Can you post a short but program that we can copy/paste for testing? Make sure the program is complete, including the #device and #fuse lines.
SuperAlpha



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PostPosted: Wed May 09, 2007 9:25 am     Reply with quote

I am using PCH compiler v4.021.
SuperAlpha



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PostPosted: Wed May 09, 2007 9:27 am     Reply with quote

The typo is the word oscillator. This is not necessary. I have tried it with and without the additional parameters in the #use delay.
mskala



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PostPosted: Wed May 09, 2007 10:20 am     Reply with quote

Then your oscillator is not 20MHz.
SuperAlpha



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PostPosted: Wed May 09, 2007 4:03 pm     Reply with quote

#pragma use delay(clock=20M, restart_wdt)
delay_ms(20);

or

#pragma use delay(clock=20M)
delay_ms(20);


I still see a delay from about 16-18ms, never >=20ms.
PCM programmer



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PostPosted: Wed May 09, 2007 4:08 pm     Reply with quote

1. Post your PIC.

2. Also tell us how you are determining that the delay period is shorter
than expected. Are you measuring it with an oscilloscope or a logic
analyzer ?

3. Post a very short (but compilable) program that demonstrates the
problem.

4. Are you running actual hardware or is this being done in Proteus ?
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