>I am using a PIC18F1320 with the MPLAB compiler. I wrote the code, 
>and
> while testing it I get a set of outputs with the oscilloscope, but
> when i disconnect the oscilloscope, the outputs are different.
> For example, I read in a byte over the serial port and compare it 
> with
> a variable. If it matches then I light an LED. With the oscilloscope
> connected the LED never lights, without it it does.

You may have an input driven by a high impedance. Oscilloscope loading 
may affect this. It is most unlikely that oscilloscope loading will 
affect a properly configured output.

Oscilloscope load is typically of the order of 1 Mohm and 10 pF. It 
can affect oscillator operation under marginal conditions but usually 
only if connected to the oscillator circuit in some way.

Is your reset line properly managed?



        Russell



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