[time-nuts] Modeling vs reality question re my TIC

Bruce Griffiths bruce.griffiths at xtra.co.nz
Mon Mar 10 16:53:19 EDT 2014

Metastability in the Flipflops?

Charge injection when tristating tristate buffers?

Neither of which are included in your models.


Bob Stewart wrote:
> Fellow Timenuts:
> I'm trying to square reality with the modeling that I did, and nothing makes
> sense.  When I modeled the result of just my 2.4K resistor with the caps and resistor the PIC datasheet says it has in it, there's no relationship.  The model says
> I'll get millivolts out.  Here's how I calculate what I'm actually
> getting:
> ADC VRef is 2.5V
> 10-bit ADC = 1024 positions
> Max ADC from TIC = 975
> 975/1024*2.5 = 2.38V Max TIC value
> Min ADC from TIC = 293
> 293/1024*2.5 = 0.715V Min TIC value
> A range of 0.715V-2.38V is totally outside my expectations.  The only way I can get close to these values is if the internal CHOLD in the PIC is only a fraction of the 120pf they say it has - say 20pf.  Any thoughts would be appreciated.
> Bob - AE6RV
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