Re: Measurement Computing pci-das6* timing error

On Wednesday 16 November 2005 04:55 pm, Derek Foreman wrote:
> Hi,
>
> (I posted this briefly a few months ago)
>
> I'm using a measurement computing pci-das6036 card, acquiring 10
> channels at 20khz.
>
> Measuring the STARTSCAN signal with an oscope showed the actual sampling
> rate to be 19.997khz or so.
>
> It looks to me like the (rather spartan) register map's note that
> "ADC Pacer Frequency = Base_clock/(Divider + 3)"
> for the ADC Sample interval also applies to the Delay interval.
>
> With the following patch in place, I sample at 20khz as intended.
>
> Anyone know if this is the right thing to do, and if it isn't... what
> is?

It's fine in principle, although the same minus 3 would need to be applied 
to the TRIG_TIMER case also.  I didn't apply your change before because 
when I wrote that code originally I checked it on my board (a 6025 I 
think) and it was right.  I was going to check again but never got around 
to it and forgot about it (sorry).  To be sure what you're seeing is real 
and not just due to your board oscillator being a little off you need to 
do it again with 1 channel at 200khz.  If it is real, the percent error in 
actual sampling rate should increase by a factor of 10 (that is, a 100 
times larger error in frequency).

-- 
Frank