delay_ms() issues - being shorted on time!

SuperAlpha · Joined: 19 Apr 2007 Posts: 4 Location: DFW, TX

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 Posts: 3680 Location: The Netherlands

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 · Joined: 19 Apr 2007 Posts: 4 Location: DFW, TX

I am using PCH compiler v4.021.

SuperAlpha · Joined: 19 Apr 2007 Posts: 4 Location: DFW, TX

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 · Joined: 06 Mar 2007 Posts: 100 Location: Massachusetts, USA

Then your oscillator is not 20MHz.

SuperAlpha · Joined: 19 Apr 2007 Posts: 4 Location: DFW, TX

#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 · Joined: 06 Sep 2003 Posts: 21708

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 ?