Accurate Freq Measurment

[amgen]

Bruce & Terry,
I have been following posts on freq measure. That timer 5 with the motion feedback module is just super-neat. Hardly any code to get very accurate measure. Being able to measure small ,small errors is amazing.
Terry, if you don't mind, how much are your readings varying around the 4khz and what clock did you end up using?
Also, what are you doing with the output value?
Hats off to you guys.
don
amgen

[Terry]

Don,
I have been experimenting with both the prescaler (divide by 16) and skipping it. When I use an Agilent frequency generator for testing, the count only jitters by 1 count with either approach, the measurement is very stable under this test situation with both approaches. Now that I have the PIC code working, I am now experimenting with my actual application to see which is the better method.
When measuring the period of 200 cycles of a 4 kHz signal, the frequency resolution is great, 1 count corresponds to 0.016 Hz at 4 KHz and the measurement time is 50 msec. The PIC counters are great once you understand how to set them up.
I output the count data via RS-232 to a PC.
Terry

[davidcope]

Hi,

I've read the great advice and example code here during a search of PIC period measurement. I'm in the process of using a PIC 18F2431 and using C.

Not being an expert with PICBasic, could I ask what PIR3.1 refers too from the example given above?

Capture VAR PIR3.1

Thanks in advance, David.

[Acetronics2]

Hi,

"C" ... What is "C" ...

is there anything called "C" somewhere ????

has "C" ever existed ???

Just open your pic datasheet, interrupts flags section ... you'll find it.

BTW : VAR ... just means " other name for " ( something like # DEFINE ... Ooops ... )

Alain

[Bruce]

PIR3.1 is bit #1 in the PIR3 register. Capture VAR PIR3.1 just creates an alias for this interrupt flag bit.

[davidcope]

PIR3.1 is bit #1 in the PIR3 register. Capture VAR PIR3.1 just creates an alias for this interrupt flag bit.

Many thanks Bruce that makes it perfectly clear.

@Alain Thanks too. Apologies for mentioning the "C" letter BTW!

As for the RTFM thing. Please, it's a cop out. It's the easiest thing in the world to belittle someone for not finding the information (or quite understanding how to frame a question) you may think should be obvious, but in the context of the wider picture may not be to the person asking the question. And of course the "Problem" may only be one of several or several tens that the poster may be concurrently dealing with at the time of the question.

Sorry Alain, I really don't mean to appear to be negative after you've been kind enough to reply to my question, it's just that RTFM is so often used to limit learning, not encourage it.

So yes, I see now that Section 10.2 (Page 102) "PIR Registers" of the data sheet provides the information for the code I was referring to. That's one problem down...many more to go.

Thanks again for your inputs. David.