Lpc2000

This method works very well for low frequencies, but it can have
substantial error at high frequency where multiple interrupts are
running. The interrupt latency will cause a slight delay in capturing
the time base.  If this is always the same, it washes out. But if
another - higher priority - task sometimes runs, there will be jitter in
the latency - causing jitter in the frequency measurement.

 

Using counters for high frequency works well, but with high load. Using
edge-edge timers works very well for low frequencies.

 

  _____  

From: lpc2000@yahoogroups.com [mailto:lpc2000@yahoogroups.com] On Behalf
Of Martin Maurer
Sent: Thursday, June 09, 2005 10:29 PM
To: lpc2000@yahoogroups.com
Subject: Re: [lpc2000] Re: Frequency counter

 

Hello,

i don't know if there is any hardware support for this ?

Here are two not elegant solutions, but give you perhaps an idea !

Easiest way without hardware support: Measure the time between line
going 
low->high and second low->high.

WaitForPinLow();
WaitForPinHigh();
for(t1 = 0; t1 < BigTimeoutValue; t1++)
{
    WaitForPinLow();
}
for(t2 = 0; t2 < BigTimeoutValue; t2++)
{
    WaitForPinHigh();
}

According to values t1 and t2 (in sum) you can get the frequency.

BUT: This is very compiler dependant, if it does any optimization,
values 
can change !

Better use one of the timers: Start a timer with high frequency, read it
out 
the first time low->high and read it out the second time low->high. Then
you 
can calculate the frequency.

Regards,

         Martin


----- Original Message ----- 
From: "lehighuboy" <garrett.j.young@...>
To: <lpc2000@yahoogroups.com>
Sent: Friday, June 10, 2005 7:18 AM
Subject: [lpc2000] Re: Frequency counter


>I need to read the frequency of a 50% duty cycle waveform from 0 to
> 200kHz (+/- 1Hz) using the LPC2129. Any suggestions?
>
> Thanks, Garrett
>
> --- In lpc2000@yahoogroups.com, "lehighuboy" <garrett.j.young@g...>
> wrote:
>> Does anyone have sample code that counts pulses for a fixed time
>> duration (frequency counter)?
>>
>> Thanks, Garrett
>
>
>
>
>
> Yahoo! Groups Links
>
>
>
>
>
>
>
> 




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