Hi Dan,

The first thing I would try would be to use a bigger capacitor. See if the
results are closer to predicted then. Also, make sure that you are setting
the PIC up in RC mode (using the configuration word in your assembler).
BTW, does the waveform look right on your scope? I think it should look
like a sawtooth wave on OSC1 and a square wave on OSC2.

Good luck,

Sean


At 02:45 PM 12/14/98 -0800, you wrote:
>Hi all,
>
>I wonder if anyone can help me understand the strange results I see
>when I point my oscilloscope at the OSC pins of my 16f84. I've got a
>wire-wrapped prototype with an RC oscillator connected to OSC1. Current
>values of R and C are 10K Ohms and 20pF. I also looked at the same
>circuit with the 20pF cap removed--I imagine the wire-wrapping, etc.
>provides enough capacitance to get the oscillator going.
>
>Estimating the frequencies with my $20 flea market oscilloscope I get:
>
>                w/20pF cap              w/o cap
>
>        OSC1    290khz                  310kHz
>
>        OSC2    670kHz                  2.2mHhz
>
>
>So my first question is, why am I not seeing the roughly 2.5mHz predicted
>in the data sheet for these values of R and C.
>
>More puzzling, though, is that I don't see anything like the expected 4/1
>ratio of OSC1's frequency to OSC2's frequency. In fact, OSC2's frequency is
>always at least twice that of OSC1.
>
>Any clues? (BTW, I wouldn't rule out anything obvious--I'm very much a
>beginner at this stuff.)
>
>
>Dan
>
+-------------------------------+
| Sean Breheny                  |
| Amateur Radio Callsign: KA3YXM|
| Electrical Engineering Student|
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