Hello!
As part of my microcontrollers class, there is a VERY basic assignment: Hook up a crystal resonator as shown in the datasheet.
I have done so, and I believe this is well-known enough that I shouldn't have to include a schematic (though I can make and upload one if it's necessary).
It works great, I have used the 20MHz crystal for many projects already in this configuration. The problem is in trying to use a scope to read that frequency. As soon as I apply the probe, oscillation stops, the PIC does not move to the next instruction. I have a LED "traffic light" that constantly cycles, but probing either the clock input or clock output on the PIC (16F877A), the oscillation stops.
I am only trying to do this because it's stated as a step in my school workbook. However, I note that in the book, the author is actually using a 20MHz OSCILLATOR (4-pin package) rather than the crystal. She states that they are basically the same.
I suspect that if I had the Oscillator and not just the crystal that I would be able to measure this frequency.
I also suspect that the impedance of the probe is loading the resonator circuit, but I don't understand this.
My questions are:
Why does attempting to measure this frequency cause the oscillations to stop?
Would this happen if I used an oscillator instead?
Thanks!
As part of my microcontrollers class, there is a VERY basic assignment: Hook up a crystal resonator as shown in the datasheet.
I have done so, and I believe this is well-known enough that I shouldn't have to include a schematic (though I can make and upload one if it's necessary).
It works great, I have used the 20MHz crystal for many projects already in this configuration. The problem is in trying to use a scope to read that frequency. As soon as I apply the probe, oscillation stops, the PIC does not move to the next instruction. I have a LED "traffic light" that constantly cycles, but probing either the clock input or clock output on the PIC (16F877A), the oscillation stops.
I am only trying to do this because it's stated as a step in my school workbook. However, I note that in the book, the author is actually using a 20MHz OSCILLATOR (4-pin package) rather than the crystal. She states that they are basically the same.
I suspect that if I had the Oscillator and not just the crystal that I would be able to measure this frequency.
I also suspect that the impedance of the probe is loading the resonator circuit, but I don't understand this.
My questions are:
Why does attempting to measure this frequency cause the oscillations to stop?
Would this happen if I used an oscillator instead?
Thanks!