Gerhard wrote
>
> Ok, this doesn't look like a normal pull-down logic output :)  Just to 
> have
> one more data point: what pull-up resistor did you use?
>

See below

>
> I'm a bit reluctant to ask because it doesn't make much sense, but did you
> really have the resistor in series to the scope?
>
>
>> Somewhere I read that if your signal drops in half with a certain
>> resistance, then that is probably the source impedance.
>
> Kind of... Goes like this (ASCII art following :)
>
>  +-------Ri------o------+-------+
>  |                      |       |
> ideal                   |       |
> voltage                 Rl     volt
> source                  |      meter
>  |                      |       |
>  +---------------o------+-------+
>
>


I had it like this before:

  +-------Ri------o------R1------+
  |                              |
 ideal                           |
 voltage                       volt
 source                        meter
  |                              |
  +---------------o--------------+

When I took the screenshots, I had the circuit like the one above, where R1 
is the potentiometer. I redid the same tests using the circuit you suggested 
and I had very different results. For example, the edges of the waveform did 
not change significantly (it was still a square wave), and when it dropped 
to 2V, R1 was 800 ohms.

Then I did two other tests using CCP1, one pulling the signal up with a 6.8K 
resistor, and the other using an opamp. In both situations my system worked, 
but somehow using the voltage buffer it was less jittery. What I mean by 
jittery: I'm outputting the pulse width in microseconds to an LCD. In the 
first case (pullup), the value output to the LCD would oscillate +/-5 us, 
and with the voltage buffer it rarely oscilated.


>
> However, and that seems to be what you did, when you put Rl in series to
> the volt meter (or scope), this doesn't give the same results. Assuming
> that the scope's impedance is much higher than Ri, the load of the source
> didn't change significantly. What did change is the amount of the voltage
> that the scope got to see... your scope probe has an impedance of 1M,
> right?

Yes

> It seems to be that there's something wrong with your port. Maybe the port
> configuration, other components connected to the port, a short somewhere,
> or the chip.


Humnn, now that you're saying that, one other thing that I found weird. I've 
double checked and TRISC.2 is really set to input, but if I measure the 
voltage on that pin when floating, it reads close to 1V. Is that normal? Is 
it because it is floating or any other mysterious effect such a leak in 
clamp diodes?

I think I'll go ahead and use the v.buffer (it is not a production board and 
I have the ICs, so I guess it won't hurt) and that solves my problem, but 
this discussion is being very educational for me.

Thanks a bunch

Padu


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